Human Molecular Genetics

Human Molecular Genetics Advance Access originally published online on September 2, 2003

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Human Molecular Genetics, 2003, Vol. 12, Review Issue 2 R249-R257
DOI: 10.1093/hmg/ddg298
© 2003 Oxford University Press

A fragile balance: FMR1 expression levels

Ben A. Oostra^* and Rob Willemsen

Department of Clinical Genetics, Erasmus MC, Rotterdam, The Netherlands

Received June 30, 2003; Accepted August 14, 2003

	ABSTRACT

TOP ABSTRACT PREVALENCES AND CGG-REPEAT... FEMALE PREMUTATION CARRIERS MALE PREMUTATION CARRIERS UNEXPECTED PHENOTYPE IN MALE... STRUCTURAL DOMAINS OF FMRP mRNA TARGETS OF FMRP ROLE OF FMRP IN... FMRP AND mRNP TRANSPORT FMRP AND LTD REFERENCES

 
The FMR1 gene is involved in three different syndromes, the Fragile X syndrome, premature ovarian failure (POF) and the Fragile X-associated tremor/ataxia syndrome (FXTAS) at older age. Fragile X syndrome is caused by an expanded CGG repeat above 200 units in the FMR1 gene resulting in the absence of the FMR1 mRNA and protein. The FMR1 protein is proposed to act as a regulator of mRNA transport and/or translation that plays a role in synaptic maturation and function. POF and FXTAS are found in individuals with an expanded repeat between 50 and 200 CGGs and are associated with increased FMR1 mRNA levels. The presence of elevated FMR1 mRNA in all patients suggests that these syndromes may represent a gain-of-function effect from the elevated message levels. The level of FMR1 mRNA is in fragile balance and is therefore critical for normal functioning.

Fragile X syndrome is the most prevalent cause of heritable mental retardation with a frequency of 1 : 4000 males and 1 : 6000 females (reviewed in 1). This X-linked disorder is usually caused by the absence of the fragile X mental retardation protein (FMRP). In addition, a rare atypical case of Fragile X syndrome has been reported that is associated with a single point mutation (2). The subcellular distribution of FMRP is largely cytoplasmic and FMRP expression is widespread with abundant expression in neurons, in dendrites in particular, and with testicular expression in spermatogonia (3,4). The association of FMRP with ribosomes is mRNA-dependent via ribonucleoprotein (RNP) particles, which contain several other proteins like nucleolin, YB-1, NUFIP1, CYFIP1 and CYFIP2 and the fragile X (structurally) related proteins FXR1P and FXR2P (5–7). FMRP contains RNA-binding sequence motifs, including two KH domains and an RGG box (8,9). The precise physiological function of FMRP is still not defined; however, a role in transport and/or translational efficiency of mRNAs, including its own mRNA, has been suggested (10).

	PREVALENCES AND CGG-REPEAT INSTABILITY

TOP ABSTRACT PREVALENCES AND CGG-REPEAT... FEMALE PREMUTATION CARRIERS MALE PREMUTATION CARRIERS UNEXPECTED PHENOTYPE IN MALE... STRUCTURAL DOMAINS OF FMRP mRNA TARGETS OF FMRP ROLE OF FMRP IN... FMRP AND mRNP TRANSPORT FMRP AND LTD REFERENCES

 
In fragile X syndrome, mental retardation is almost exclusively caused by an expansion of a polymorphic CGG repeat in the 5' untranslated region of the FMR1 gene (11,12). Fragile X patients have a number of more than 200 units. As a result of the repeat expansion, the CGG repeat and the surrounding promoter region of the FMR1 gene is methylated, inhibiting FMR1 transcription and causing absence of the protein product.

Although the number of CGG repeats in the general population is highly variable, the majority of FMR1 alleles have 29–30 repeats and are stable upon transmission to the next generation (13). These normal CGG repeats in the FMR1 gene are usually interrupted by two AGG triplets. Individuals with the fragile X premutation (PM) have expanded repeat lengths varying from 50 to 200 CGG repeats. PM alleles may become unstable, however, only through maternal transmission, and lengths usually increase in subsequent generations. Previous estimates of the prevalence of PMs in the general population in Canada yielded a prevalence of 1 : 259 females and 1 : 813 males with more than 54 repeats (14). Interestingly, this population-based study in males identified a number of alleles of intermediate size (between 40 and 54 CGG repeats) that, next to the identified PM alleles, showed AGG interruptions, suggesting that loss of AGG interruptions is a late event in the expansion of normal CGG repeats to intermediate sized alleles. Other studies in both Israel and Italy showed actually higher prevalences of PM alleles with prevalences approaching 1 : 100 females (15,16); however, further population-based screening studies in different populations are necessary to determine accurate estimates of PM alleles in the general population.

A recent collaborative study was established to examine several issues regarding FMR1 CGG-repeat instability among females with PM and intermediate alleles (17). Nolin and co-workers (17) found that the smallest alleles to undergo expansion to full mutation in one generation contained 59 CGG repeats with no AGG interruptions, and accurate risk estimates of full-mutation expansions in offspring of females with PM-size alleles were lower than previously supposed. Furthermore, no significant sex bias was observed in the proportion of full mutation offspring born to mothers with PM alleles, and in contrast to PM alleles the intermediate alleles from females with no family history of fragile X, as a group, exhibited a stable transmission pattern. Notably, in contrast to PM-size alleles, Sullivan et al. (18) observed a higher degree of instability in paternal transmission of intermediate alleles. Altogether, these epidemiological studies are not only important to provide knowledge about the mutational pathway of repeat instability and understanding of FMR1 PM penetrance but also allow clinicians to improve risk estimates for genetic counselling of females with PM or intermediate-size alleles in making decisions about prenatal diagnosis.

	FEMALE PREMUTATION CARRIERS

TOP ABSTRACT PREVALENCES AND CGG-REPEAT... FEMALE PREMUTATION CARRIERS MALE PREMUTATION CARRIERS UNEXPECTED PHENOTYPE IN MALE... STRUCTURAL DOMAINS OF FMRP mRNA TARGETS OF FMRP ROLE OF FMRP IN... FMRP AND mRNP TRANSPORT FMRP AND LTD REFERENCES

 
Cognitive functioning in female PM carriers is generally considered normal; however, a small subset of female PM carriers develops mild learning disabilities and emotional problems such as mood lability and anxiety (1). More importantly, 20% of female PM carriers manifest premature ovarian failure (POF), defined by menopause before 40 years. POF represents the final stage of a variety of diseases that result in the loss of ovarian follicles. Hundscheid et al. (19) reported evidence for a paternal-parent-of-origin effect on POF in female PM carriers; however, subsequent studies by others did not support this observation (20,21). Differences between the different data sets may be related to the observed discrepancy. Perhaps the variation in FMR1 transcript levels in female PM carriers contributes to the development of POF (22). Further investigations are needed to understand the molecular pathways underlying POF among PM carriers, including the role of increased FMR1 transcripts on follicular development (23).

	MALE PREMUTATION CARRIERS

TOP ABSTRACT PREVALENCES AND CGG-REPEAT... FEMALE PREMUTATION CARRIERS MALE PREMUTATION CARRIERS UNEXPECTED PHENOTYPE IN MALE... STRUCTURAL DOMAINS OF FMRP mRNA TARGETS OF FMRP ROLE OF FMRP IN... FMRP AND mRNP TRANSPORT FMRP AND LTD REFERENCES

 
Male PM carriers have generally been thought not to develop mental disabilities because they produce normal levels of the FMR1 gene product, FMRP. Recent studies of the expression of the FMR1 gene show compelling evidence that in cells of males with alleles in the PM range significantly increased FMR1 mRNA levels can be detected. The increased transcriptional activity of the FMR1 gene seems to be positively correlated with the size of the CGG repeat. That is, CGG repeats in the upper range (100–200 CGGs) result in an average 5-fold elevation, whereas CGGs in the lower range (50–100 CGGs) result in an average 2-fold elevation (22,24,25). Paradoxically, FMRP levels in cells from male PM carriers were mildly reduced (24,25). This observation has led to the hypothesis that expanded CGG repeats lead to the translational impediment of the FMR1 transcripts by conformational changes in the FMR1 transcript that influence the initiation of translation and stalled 40S ribosomal subunits and consequent FMRP reduction (22,24,25). Such a mechanism has been proposed for unmethylated alleles in the fragile X full mutation range too (26). In cells with alleles in the PM range the increased transcriptional activity of the FMR1 gene could be caused by a feedback mechanism for the diminished translational efficiency of the FMR1 transcript (Fig. 1). However, direct proof for such a mechanism is lacking and several other possible explanations for the enhanced transcriptional activity of the FMR1 gene have been proposed, including more open promoter conformation due to the expanded CGG repeat (25), and up-regulation of transcription by CGG binding proteins such as CGGBP1, a protein known to be able to regulate FMR1 expression (27). Increased stability of the FMR1 transcripts due to expanded CGG repeats has been excluded as an alternative explanation (24). In addition, the normal FMR1 transcript levels in the mutant I304N cell line argues against a role for the lack of functional FMRP as regulator of transcriptional activity of the FMR1 gene (22,25). The reduced FMRP production despite elevated FMR1 transcript levels suggests that transcriptional reactivation of the FM alleles as therapeutic intervention of fragile X syndrome will not be an effective therapy and thus should also include strategies to circumvent the block at the level of translation initiation.

View larger version (47K): [in this window] [in a new window]   Figure 1. Proposed model for molecular neuropathology in fragile X associated tremor/ataxia syndrome. (1) FMR1 transcripts containing an expanded CGG repeat are normally incorporated in a mRNP particle and translocated out of the nucleus. (1a) The long CGG repeat in the FMR1 transcript impede 40S ribosomal subunit migration resulting in hampered translation. Consequently, the nerve cell produces reduced levels of FMRP, the gene product of the FMR1 gene. (2) In response to lowered FMRP levels an up to now unidentified feedback mechanism may increase the level of specific transcription factors that results in increased transcription of the FMR1 gene. Enhanced transcription leads to elevated FMR1 mRNA levels. Alternatively, long CGG tracts in the FMR1 transcript may sequester high quantities of CGG-binding proteins and lowered CGG-binding protein levels result in an increased FMR1 transcription. (3) The nerve cell attempts to clear itself from elevated FMR1 transcript levels by employing molecular chaperones, and components of the ubiquitin–proteasome degradation pathway. If elevated FMR1 transcript levels resists refolding/degradation intranuclear inclusions will be formed. Ultimately, the formation of inclusions will trigger neurodegeneration by activation of neurotoxic signalling pathways. Here, several mechanistic pathways can influence this process.

 

	UNEXPECTED PHENOTYPE IN MALE PM CARRIERS

TOP ABSTRACT PREVALENCES AND CGG-REPEAT... FEMALE PREMUTATION CARRIERS MALE PREMUTATION CARRIERS UNEXPECTED PHENOTYPE IN MALE... STRUCTURAL DOMAINS OF FMRP mRNA TARGETS OF FMRP ROLE OF FMRP IN... FMRP AND mRNP TRANSPORT FMRP AND LTD REFERENCES

 
The recent description of older males carrying a PM (ranging between 71 and 135 CGGs, to date), who exhibit an unique neurodegenerative syndrome characterized by progressive intention tremor and ataxia (FXTAS; fragile X-associated tremor/ataxia syndrome) suggests that a new neurodegenerative disorder has been linked to the PM state (28). More advanced cases may be accompanied by memory and executive function deficits, anxiety, parkinsonism, peripheral neuropathy, essential tremor and autonomic dysfunction (28–32). Significant dementia has been observed in a limited number of patients (28,33). MR imaging studies (T₂ signal) of the brain of symptomatic adult male premutation carriers showed a characteristic imaging, including hyperintensities of the middle cerebellar peduncle, cerebellar white matter lateral, superior and inferior to the dentate nuclei and volume loss involving the pons, mesencephalon, cerebellar cortex, cerebral cortex, white matter of the cerebral hemispheres, and corpus callosum (34). Neurohistological studies on the brains of four symptomatic elderly premutation carriers demonstrated neuronal degeneration in the cerebellum and the presence of eosinophilic intranuclear inclusions in both neurons and astroglia. Furthermore, the inclusions showed a positive reaction with anti-ubiquitin antibodies, which suggests a link with the proteasome degradation pathway (33).

To better understand the timing and mechanism involved in FMR1 CGG repeat instability and methylation, a mouse model has been generated in which the endogenous mouse CGG repeat was replaced by a human CGG repeat carrying 98 CGG units (35). This ‘knock-in’ CGG triplet mouse shows moderate CGG repeat instability upon both maternal and paternal transmission and the aging ‘knock-in’ CGG triplet mouse was used to study the pathogenesis of FXTAS in these mice. Neurohistological, biochemical and molecular studies of the brains of these expanded-repeat mice (20–72 weeks) were undertaken and elevated Fmr1 mRNA levels and intranuclear inclusions with ubiquitin, Hsp40 and the 20S catalytic core complex of the proteasome as constituents were reported (Fig. 2) (36). An increase was observed in both the number and the size of the inclusions in specific brain regions during the course of life, which correlates with the progressive character of FXTAS. These observations in expanded-repeat mice support a direct role of the Fmr1 gene, by either CGG expansion per se or by elevated Fmr1 mRNA levels, in the formation of the inclusions and suggest a correlation between the presence of intranuclear inclusions in distinct regions of the brain and the clinical features in symptomatic premutation carriers. This mouse model will facilitate molecular studies to further analyse the pathogenesis of FXTAS from onset of symptoms till the final stage of the disease.

View larger version (157K): [in this window] [in a new window]   Figure 2. Immunohistochemical localization of Hsp40 in paraffin embedded brain tissue of expanded-CGG repeat mice at the age of 72 weeks by an indirect immunoperoxidase technique. In this micrograph Hsp40 is present in intranuclear neuronal inclusions in the parafascicular thalamic nucleus. Notably, the number of Hsp40-positive inclusions was less compared to the number of ubiquitin-positive inclusions (300x).

 
The origin and constitution of the inclusions in FXTAS is poorly understood; however, the presence of elevated FMR1 mRNA levels in all patients has been proposed to be important for the formation of the inclusions and may represent a gain-of-function effect from the elevated message levels (29,33). A toxic RNA gain-of-function effect by non-coding portions of mRNAs, containing expanded repeats, has been proposed for several triplet repeat-related ataxias, such as SCA8, SCA10 and SCA12 and both genetically characterized forms of myotonic dystrophy (DM1 and DM2) (37). Extensive studies in both forms of DM1 and DM2 have shown that expanded tracts of CUG and CCUG repeats, respectively, within the untranslated part of the mRNA sequestered nuclear CUG-binding proteins which disrupts either mRNA processing (splicing) of other genes or transport of other mRNAs, eventually leading to abnormal muscle differentiation in both DM1 and DM2 and insulin resistance in DM1 (38–43). Whether the phenotype in male PM carriers arises from a similar mechanism is unknown; however, the expanded CGG tract in the FMR1 mRNA may attract high quantities of CGG-binding proteins with a consequent cumulative cytotoxic effect that may lead to intranuclear inclusion formation and ultimately neuronal cell death (27,44).

The presence of components of the ubiquitin–proteasome pathway and molecular chaperones is shared with several hereditary ataxias and other trinucleotide repeat disorders, including Huntington's disease (45,46), SCA type 1 (47), SCA type 3 (48), SCA type 7 (49) and OPMD (50). For the polyglutamine disorders a model has been proposed in which the polyglutamine expansion has a toxic gain-of-function property on the protein. However, a direct cause-and-effect relation between nuclear inclusions and the disease mechanisms is still under debate (51–53). Recent studies of cellular models of polyglutamine diseases point to impaired proteasome function in the presence of polyglutamine fragments; however, it has been suggested that the impaired protein clearance is only at the start of the pathogenesis. The formation of aggregates seems to be a healthy response to misfolded proteins. For instance, the knock-in SCA1 mice (154Q) show exactly the abundant number of inclusions in neurons that are spared neurodegeneration, whereas Purkinje cells are the last to form inclusions (54). The cellular consequences of perturbation of the ubiquitin–proteasome degradation pathway in polyglutamine disorders may include transcriptional dysregulation of specific genes or sequestering of important proteins such as transcription factors and molecular chaperones, potentially leading to neuronal cell death (55–57). In addition, a recent study from Cowan et al. (58) suggest that abnormal stress response may contribute to the enhanced cell vulnerability. Cells expressing a truncated form of the androgen receptor containing an expanded polyglutamine tract show a reduction in the available levels of a specific heat shock protein involved in stress response (Hsp72). It was hypothesized that polyglutamine protein aggregates perturb normal stress response to routine metabolic insults and increase cell vulnerability. Whether the formation of aggregates underlies the clinical symptoms in male PM carriers remains unsolved.

It should be noted that mechanistically the FXTAS appears to fall into a different class of disorders than the polyglutamine diseases. That is, the expanded CGG repeat in the FMR1 gene is located in a non-coding region of the gene, whereas the expanded CAG repeat is located in each gene's coding region, resulting in a polyglutamine tract in the disease protein. Thus, FXTAS seems to be caused by a pathogenic mechanism at the RNA level (dominant RNA-gain-of-function), wherein CGG repeat expansions in the FMR1 transcript disturb cellular function, finally leading to cell death.

Finally, the recognition of FXTAS as a new neurological disorder associated with older male PM carriers has implications for genetic counselling of fragile X families. Preliminary studies suggest that FXTAS occurs in 20–30% of male PM carriers. With a population frequency of the PM carrier state of 1 : 813 males, FXTAS also represents a significant group in idiopathic ataxia. An initial analysis for the presence of the fragile X premutation in a cohort of 59 patients referred for genetic analysis of SCA genes showed three patients to carry the premutation (59). Further research should be focused on the true incidence of FXTAS among male PM carriers, the constituents of the inclusions and whether the elevated FMR1 transcripts are related etiologically to the formation of the inclusions.

	STRUCTURAL DOMAINS OF FMRP

TOP ABSTRACT PREVALENCES AND CGG-REPEAT... FEMALE PREMUTATION CARRIERS MALE PREMUTATION CARRIERS UNEXPECTED PHENOTYPE IN MALE... STRUCTURAL DOMAINS OF FMRP mRNA TARGETS OF FMRP ROLE OF FMRP IN... FMRP AND mRNP TRANSPORT FMRP AND LTD REFERENCES

 
Two types of RNA binding domains have been identified in FMRP, including two KH domains and an RGG box containing a conserved Arg–Gly Gly triplet (8,9). The importance of the KH domain for a proper FMRP function is illustrated by a rare, unique patient with an Ile304Asn mutation, located in the second KH domain (2). The mutation disrupts the normal folding of the KH domain.

In addition, a nuclear localization signal (NLS), a nuclear export signal (NES), two coiled coils and a G-quartet binding structure have been identified. The presence of both a NES and NLS suggests that the fragile X protein shuttles through the cell into and out of the nucleus (Fig. 3). The nuclear export mediated by the NES of FMRP is exportin1-dependent (60). In accordance with the shuttling hypothesis, the protein has been observed in the nuclear pore during transfer between the nucleus and cytoplasm (61).

View larger version (35K): [in this window] [in a new window]   Figure 3. Schematic representation of a hippocampal neuron. (A) The apical dendrite with its synaptic spines is blown up. FMRP is cytoplasmic and nuclear proteins thought to be involved in mRNA translation and/or dendritic transport, favoring local protein synthesis in the vicinity of (activated) synaptic spines. Specific neurotransmitters (NTs), such as glutamate, and neurotrophic factors (NTFs), such as BDNF, through the activation of specific signaling pathways, can cause dendritic accumulation of certain mRNAs and local protein synthesis. (B) Hypothetical model of the action of FMRP in a hippocampal synapse, adapted from Huber et al. (85). Stimulation of mGluR5, a metabotropic glutamate receptor, induces local mRNA translation. This results in novel protein synthesis that on its turn stimulates the internalization of the ionotropic AMPA and NMDA glutamate receptors, both essential for in long-term plasticity. However, one of the proteins that are stimulated by mGluR5 activity is FMRP (73). As FMRP is a negative regulator of transcription (10,85), local mRNA translation might decrease as a result of the FMRP increase, slowing down the internalization of the ionotropic glutamate receptors. In neurons from fragile X patients the absence of FMRP leads to an increase of the internalization of the ionotropic glutamate receptors which results in excessive LTD.

 
In human cell lines, FMRP co-localizes primarily with polyribosomes and rough endoplasmic reticulum. There is strong evidence to support that FMRP is important in regulating mRNA translation. Evidence was presented that FMRP in vitro may function as a repressor of translation of its own mRNA (10). It is interesting to note that the Ile304Asn mutant FMRP still is able to interact with polyA-mRNA but loses its function in vitro as a translational repressor due to a loss of homo-oligomerization. Two recent papers describe FMRP-associated mRNAs as containing a sequence that can form an intramolecular G quartet structure. Schaeffer reported that FMRP binds to its own mRNA via a purine quartet that is found at the C terminal end of the part coding for the open reading frame (62). Darnell identified FMRP-bound RNA sequences out of a random RNA pool using the SELEX methodology (63). These RNA sequences had in common that they were able to form a G quartet structure G quartets in RNA have been implicated in the repression of mRNA translation and in RNA turnover, which is in line with the in vitro repression experiments, described by Laggerbauer (10). The presence of a G quartet structure in the FMRP associated mRNAs may indicate a high level of selectivity as only 4% of the mRNAs contain a G quartet structure.

	mRNA TARGETS OF FMRP

TOP ABSTRACT PREVALENCES AND CGG-REPEAT... FEMALE PREMUTATION CARRIERS MALE PREMUTATION CARRIERS UNEXPECTED PHENOTYPE IN MALE... STRUCTURAL DOMAINS OF FMRP mRNA TARGETS OF FMRP ROLE OF FMRP IN... FMRP AND mRNP TRANSPORT FMRP AND LTD REFERENCES

 
As FMRP has RNA binding capacities, identifying the mRNAs bound by FMRP in the cell is a pre-requisite for understanding its function. An interaction of FMRP with the 3'-UTR of the myelin basic protein mRNA was found using purified recombinant FMRP. Sung et al. (64) identified nine mRNAs from adult brain that are able to bind FMRP, including a neuronal NT2 EST and Tip60a, a tat interactive protein. Also the Xenopus elongation factor 1A, xEF-1A, binds strongly to human FMRP. FMRP was demonstrated to inhibit mRNA translation of this gene and, in the absence of FMRP, the translation of human EF-1A is derepressed (65).

Brown et al. (66) examined FMRP-associated mRNAs from mouse brain and human lymphocytes. Using microarrays they identified 432 mouse mRNAs that were selectively immunoprecipitated in FMRP ribonucleoprotein particles and 251 human mRNAs that appeared differentially present in polysomes of lymphoblast cells compared to cells from fragile X patients. Of 12 overlapping mRNAs identified in both data sets, eight contained a G quartet structure. It was shown that those mRNAs were either overexpressed or underexpressed in brains of individuals with fragile X syndrome. Among the identified mRNAs are the important neuronal proteins semaphorin, the microtubule-associated protein MAP1B and NAP22, which is present in axon terminals and dendritic spines.

Miyashiro et al. (67) have developed an approach to identify the mRNA cargoes of FMRP-associated RNP particles in situ using antibody-positioned RNA amplification, called APRA. Using APRA as a primary screen discrete changes in abundance and/or subcellular distribution of a subset of mRNAs (some previously proposed FMRP targets containing G-quartet motifs and other novel FMRP target mRNAs) was observed in brain tissue from Fmr1 knockout mice. The identified mRNAs include the glucocorticoid receptor (GR). The receptor showed a change in dendritical distribution in the hippocampus of the knockout mouse. Diminished responsiveness of the receptor is compatible with learning problems observed in fragile X patient. Many of the mRNA targets were confirmed to bind to FMRP by gel shift assay and changes in protein expression levels were observed in total and synaptosomal brain extracts. However, there is little overlap with the other published mRNA targets.

Using the Fmr1 knockout mouse model, Zalfa et al. (68) revealed that FMRP regulates translation of specific dendritic mRNAs. Interestingly, FMRP associates directly with the dendritic, non-messenger RNA BC1, and BC1 is able to form an RNA duplex with a number of mRNAs that are potential targets for FMRP, via base-pairing to this mRNA. This suggests that FMRP acts through BC1, thereby determining the specificity of FMRP function via a novel mechanism of translational repression. The precise mechanism of the proposed BC1-facilitated FMRP repression is still not defined; however, two binding modes for the target mRNAs of FMRP have been identified now either defined by BC1 base-pairing or G-quartet recognition. Perhaps both modes occur in the nerve cell and are linked to specific functions, e.g. transport to different postsynaptic target sites.

	ROLE OF FMRP IN THE DENDRITES

TOP ABSTRACT PREVALENCES AND CGG-REPEAT... FEMALE PREMUTATION CARRIERS MALE PREMUTATION CARRIERS UNEXPECTED PHENOTYPE IN MALE... STRUCTURAL DOMAINS OF FMRP mRNA TARGETS OF FMRP ROLE OF FMRP IN... FMRP AND mRNP TRANSPORT FMRP AND LTD REFERENCES

 
Pathological examination of brains of Fmr1 knock-out mice revealed the presence of long thin and tortuous spines along the apical dendrites (69). The presence of immature synaptic connections correlates with similar findings in human fragile X patients (70). It is postulated that FMRP by modulating mRNA translation is directly involved in synapse maturation during development and for synaptic activity in the adult.

Originally it was thought that only a few mRNAs were specifically targeted into dendrites (71). However, a recent review from Eberwine and colleagues shows the presence of many mRNAs, encoding proteins that fall into multiple functional classes within the dendrites using a very sensitive linear amplification protocol called aRNA on isolated live dendrites (72). There is compelling evidence that for dendrites an active sorting mechanism is involved.

In the synapse, FMRP might regulate the translation of certain mRNAs. Interestingly, local protein synthesis plays an important role in neuronal processes, including learning and memory. FMRP can be detected in polysomes of synaptoneurosomes, neuronal preparations highly enriched in synapses. Synaptoneurosomes respond to stimulation by metabotropic glutamate agonists with fast increasing polyribosome formation and accelerated protein synthesis.

The synthesis of FMRP in the synaptoneurosomes increases after stimulation with the neurotransmitter glutamate, suggesting that synthesis of this protein in synaptoneurosomes is triggered by a class I glutamate receptor (73). FMRP synthesis can also be affected by brain-derived neurotrophic factor, BDNF, a known regulator of synaptic plasticity (74). BDNF downregulates the FMRP expression in cultured hippocampal neurons as well as in mouse brains. This downregulation by BDNF is a response to increased tyrosine kinase receptor signalling. The decreased FMR1 mRNA amounts could be correlated to a decreased amount of FMRP in the cell.

The in vivo trigger of FMRP synthesis is not known, but FMRP increases in the barrel cortex after whisker stimulation in rats, a model of experience-dependent plasticity (75). This increase was notably observed in subcellular fractions enriched for synaptoneurosomes and polyribosomes suggesting a site-specific production of the protein. The altered level of FMRP most likely influences the translation of specific mRNAs in the synapse. Inhibition of the synthesis of its own mRNA, MAP1B, Arc and -CaMKII has been demonstrated, but it remains unclear whether all cellular RNAs that are bound by FMRP are translationally repressed.

	FMRP AND mRNP TRANSPORT

TOP ABSTRACT PREVALENCES AND CGG-REPEAT... FEMALE PREMUTATION CARRIERS MALE PREMUTATION CARRIERS UNEXPECTED PHENOTYPE IN MALE... STRUCTURAL DOMAINS OF FMRP mRNA TARGETS OF FMRP ROLE OF FMRP IN... FMRP AND mRNP TRANSPORT FMRP AND LTD REFERENCES

 
The dynamics of the transport of mRNP particles in neurons has been studied by different experimental approaches and a supramolecular complex was identified containing mRNAs, translational factors and ribosomal subunits (76–78). The migration of mRNP particles over long distances within processes towards the growth cone is established by movement along microtubules (76,79,80).

The role of FMRP in dendritic mRNA transport in vivo was studied in a PC12 (neuroendocrine) cell line stably transfected with human FMR1-GFP fusion gene with an inducible expression system (78). After induction, FMRP-GFP appeared first in the cell soma and later as large granules in the neurites. Using time-lapse microscopy the movement of FMRP-GFP-positive granules was demonstrated from the cell soma into the neurites of living PC12 cells. The movement of the granules was microtubule dependent and the average velocity of the granules was 0.2 µm/s, which is in line with granular mRNA transport kinetics (81–84). Co-localization studies showed the presence of RNA, ribosomal subunits, FXR1P and kinesin heavy chain as components of the granules (78). In Figure 3 the trafficking of FMRP from the cell soma into the dendrites is shown schematically.

	FMRP AND LTD

TOP ABSTRACT PREVALENCES AND CGG-REPEAT... FEMALE PREMUTATION CARRIERS MALE PREMUTATION CARRIERS UNEXPECTED PHENOTYPE IN MALE... STRUCTURAL DOMAINS OF FMRP mRNA TARGETS OF FMRP ROLE OF FMRP IN... FMRP AND mRNP TRANSPORT FMRP AND LTD REFERENCES

 
Since it is known that FMRP is synthesized in response to mGluR activation by glutamate (73), the involvement of FMRP in hippocampal long-term depression (LTD; long-lasting decrease in synaptic connectivity) has recently been investigated (85). In Fmr1 knockout mice, hippocampal LTD was found to be selectively enhanced compared with wild-type mice, which is consistent with a role of FMRP as repressor of translation (10,86). Stimulation of metabotropic glutamate receptors mediates internalization of AMPA and NMDA receptors and this form of LTD requires protein synthesis (87). This finding implicates FMRP in repressing translation of proteins that regulate endocytic events, and upon synaptic stimulation FMRP may dissociate from these mRNA targets to allow translation and facilitation of receptor internalization. The model predicts that in the absence of FMRP the upregulated translation of a subset of mRNAs would result in the perturbation of receptor internalisation dynamics and consequently enhanced hippocampal LTD (Fig. 3).

Thus, FMRP plays an important role in expression of proteins in the dendrites after specific triggering. Abnormal synaptic protein synthesis in absence of FMRP could underlie variable symptoms of the fragile X syndrome, including the presence of immature spines and impaired synaptic maturation.

	FOOTNOTES

 
^* To whom correspondence should be addressed at: Department of Clinical Genetics, Erasmus MC, PO Box 1738, 3000 DR Rotterdam, The Netherlands. Tel: +31 104087198; Fax: +31 104089489; Email: b.oostra{at}erasmusmc.nl

	REFERENCES

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1. Hagerman, R.J. (2002) The physical and behavioural phenotype. In Hagerman, R.J. and Hagerman, P. (eds), Fragile-X Syndrome: Diagnosis, Treatment and Research. The Johns Hopkins University Press, Baltimore, MD, pp. 3–109.

2. De Boulle, K., Verkerk, A.J., Reyniers, E., Vits, L., Hendrickx, J., Van Roy, B., Van den Bos, F., de Graaff, E., Oostra, B.A. and Willems, P.J. (1993) A point mutation in the FMR-1 gene associated with fragile X mental retardation. Nat. Genet., 3, 31–35.[CrossRef][Web of Science][Medline]

3. Devys, D., Lutz, Y., Rouyer, N., Bellocq, J.P. and Mandel, J.L. (1993) The FMR-1 protein is cytoplasmic, most abundant in neurons and appears normal in carriers of a fragile X premutation. Nat. Genet., 4, 335–340.[CrossRef][Web of Science][Medline]

4. Tamanini, F., Willemsen, R., van Unen, L., Bontekoe, C., Galjaard, H., Oostra, B.A. and Hoogeveen, A.T. (1997) Differential expression of FMR1, FXR1 and FXR2 proteins in human brain and testis. Hum. Mol. Genet., 6, 1315–1322.[Abstract/Free Full Text]

5. Ceman, S., Brown, V. and Warren, S.T. (1999) Isolation of an FMRP-associated messenger ribonucleoprotein particle and identification of nucleolin and the fragile X-related proteins as components of the complex. Mol. Cell. Biol., 19, 7925–7932.[Abstract/Free Full Text]

6. Bardoni, B., Schenck, A. and Mandel, J.L. (1999) A novel RNA-binding nuclear protein that interacts with the fragile X mental retardation (FMR1) protein. Hum. Mol. Genet., 8, 2557–2566.[Abstract/Free Full Text]

7. Schenck, A., Bardoni, B., Moro, A., Bagni, C. and Mandel, J.L. (2001) A highly conserved protein family interacting with the fragile X mental retardation protein (FMRP) and displaying selective interactions with FMRP-related proteins FXR1P and FXR2P. Proc. Natl Acad. Sci. USA, 98, 8844–8849.[Abstract/Free Full Text]

8. Ashley, C., Jr, Wilkinson, K.D., Reines, D. and Warren, S.T. (1993) FMR1 protein: conserved RNP family domains and selective RNA binding. Science, 262, 563–568.[Abstract/Free Full Text]

9. Siomi, H., Siomi, M.C., Nussbaum, R.L. and Dreyfuss, G. (1993) The protein product of the fragile X gene, FMR1, has characteristics of an RNA-binding protein. Cell, 74, 291–298.[CrossRef][Web of Science][Medline]

10. Laggerbauer, B., Ostareck, D., Keidel, E.M., Ostareck-Lederer, A. and Fischer, U. (2001) Evidence that fragile X mental retardation protein is a negative regulator of translation. Hum. Mol. Genet., 10, 329–338.[Abstract/Free Full Text]

11. Oberlé, I., Rousseau, F., Heitz, D., Kretz, C., Devys, D., Hanauer, A., Boue, J., Bertheas, M.F. and Mandel, J.L. (1991) Instability of a 550-base pair DNA segment and abnormal methylation in fragile X syndrome. Science, 252, 1097–1102.[Free Full Text]

12. Verkerk, A.J., Pieretti, M., Sutcliffe, J.S., Fu, Y.H., Kuhl, D.P., Pizzuti, A., Reiner, O., Richards, S., Victoria, M.F., Zhang, F.P. et al. (1991) Identification of a gene (FMR-1) containing a CGG repeat coincident with a breakpoint cluster region exhibiting length variation in fragile X syndrome. Cell, 65, 905–914.[CrossRef][Web of Science][Medline]

13. Kunst, C.B. and Warren, S.T. (1994) Cryptic and polar variation of the fragile X repeat could result in predisposing normal alleles. Cell, 77, 853–861.[CrossRef][Web of Science][Medline]

14. Dombrowski, C., Levesque, S., Morel, M.L., Rouillard, P., Morgan, K. and Rousseau, F. (2002) Premutation and intermediate-size FMR1 alleles in 10 572 males from the general population: loss of an AGG interruption is a late event in the generation of fragile X syndrome alleles. Hum. Mol. Genet., 11, 371–378.[Abstract/Free Full Text]

15. Pesso, R., Berkenstadt, M., Cuckle, H., Gak, E., Peleg, L., Frydman, M. and Barkai, G. (2000) Screening for fragile X syndrome in women of reproductive age. Prenat. Diagn., 20, 611–614.[CrossRef][Web of Science][Medline]

16. Toledano-Alhadef, H., Basel-Vanagaite, L., Magal, N., Davidov, B., Ehrlich, S., Drasinover, V., Taub, E., Halpern, G.J., Ginott, N. and Shohat, M. (2001) Fragile-X carrier screening and the prevalence of premutation and full-mutation carriers in Israel. Am. J. Hum. Genet., 69, 351–360.[CrossRef][Web of Science][Medline]

17. Nolin, S.L., Brown, W.T., Glicksman, A., Houck Jr, G.E., Gargano, A.D., Sullivan, A., Biancalana, V., Brondum-Nielsen, K., Hjalgrim, H., Holinski-Feder, E. et al. (2003) Expansion of the fragile X CGG repeat in females with premutation or intermediate alleles. Am. J. Hum. Genet., 72, 454–464.[CrossRef][Web of Science][Medline]

18. Sullivan, A.K., Crawford, D.C., Scott, E.H., Leslie, M.L. and Sherman, S.L. (2002) Paternally transmitted FMR1 alleles are less stable than maternally transmitted alleles in the common and intermediate size range. Am. J. Hum. Genet., 70, 1532–1544.[CrossRef][Web of Science][Medline]

19. Hundscheid, R.D.L., Sistermans, E.A., Thomas, C.M.G., Braat, D.D.M., Straatman, H., Kiemeney, L.A.L.M., Oostra, B.A. and Smits, A.P.T. (2000) Imprinting effect in premature ovarian failure confined to paternally inherited fragile X premutations. Am. J. Hum. Genet., 66, 413–418.[CrossRef][Web of Science][Medline]

20. Murray, A., Ennis, S. and Morton, N. (2000) No evidence for parent of origin influencing premature ovarian failure in fragile X premutation carriers. Am. J. Hum. Genet., 67, 253–254.[CrossRef][Web of Science][Medline]

21. Vianna-Morgante, A.M. and Costa, S.S. (2000) Premature ovarian failure is associated with maternally and paternally inherited premutation in brazilian families with fragile X. Am. J. Hum. Genet., 67, 254–255.[CrossRef][Web of Science][Medline]

22. Tassone, F., Hagerman, R.J., Chamberlain, W.D. and Hagerman, P.J. (2000) Transcription of the FMR1 gene in individuals with fragile X syndrome. Am. J. Med. Genet., 97, 195–203.[CrossRef][Web of Science][Medline]

23. Sherman, S.L. (2000) Premature ovarian failure in the fragile X syndrome. Am. J. Med. Genet., 97, 189–194.[CrossRef][Web of Science][Medline]

24. Tassone, F., Hagerman, R.J., Taylor, A.K., Gane, L.W., Godfrey, T.E. and Hagerman, P.J. (2000) Elevated levels of FMR1 mRNA in carrier males: a new mechanism of involvement in the Fragile-X syndrome. Am. J. Hum. Genet., 66, 6–15.[CrossRef][Web of Science][Medline]

25. Kenneson, A., Zhang, F., Hagedorn, C.H. and Warren, S.T. (2001) Reduced FMRP and increased FMR1 transcription is proportionally associated with CGG repeat number in intermediate-length and premutation carriers. Hum. Mol. Genet., 10, 1449–1454.[Abstract/Free Full Text]

26. Feng, Y., Zhang, F.P., Lokey, L.K., Chastain, J.L., Lakkis, L., Eberhart, D. and Warren, S.T. (1995) Translational suppression by trinucleotide repeat expansion at FMR1. Science, 268, 731–734.[Abstract/Free Full Text]

27. Muller-Hartmann, H., Deissler, H., Naumann, F., Schmitz, B., Schroer, J. and Doerfler, W. (2000) The human 20-kDa 5'-(CGG)(n)-3'-binding protein is targeted to the nucleus and affects the activity of the FMR1 promoter. J. Biol. Chem., 275, 6447–6452.[Abstract/Free Full Text]

28. Hagerman, R.J., Leehey, M., Heinrichs, W., Tassone, F., Wilson, R., Hills, J., Grigsby, J., Gage, B. and Hagerman, P.J. (2001) Intention tremor, parkinsonism, and generalized brain atrophy in male carriers of fragile X. Neurology, 57, 127–130.[Abstract/Free Full Text]

29. Hagerman, R.J. and Hagerman, P.J. (2002) The fragile X premutation: into the phenotypic fold. Curr. Opin. Genet. Dev., 12, 278–283.[CrossRef][Web of Science][Medline]

30. Jacquemont, S., Hagerman, R.J., Leehey, M., Grigsby, J., Zhang, L., Brunberg, J.A., Greco, C., Des Portes, V., Jardini, T., Levine, R. et al. (2003) Fragile X premutation tremor/ataxia syndrome: molecular, clinical, and neuroimaging correlates. Am. J. Hum. Genet., 72, 869–878.[CrossRef][Web of Science][Medline]

31. Leehey, M.A., Munhoz, R.P., Lang, A.E., Brunberg, J.A., Grigsby, J., Greco, C., Jacquemont, S., Tassone, F., Lozano, A.M., Hagerman, P.J. et al. (2003) The fragile x premutation presenting as essential tremor. Arch. Neurol., 60, 117–121.[Abstract/Free Full Text]

32. Berry-Kravis, E., Lewin, F., Wuu, J., Leehey, M., Hagerman, R., Hagerman, P. and Goetz, C.G. (2003) Tremor and ataxia in fragile X premutation carriers: Blinded videotape study. Ann. Neurol., 53, 616–623.[CrossRef][Web of Science][Medline]

33. Greco, C.M., Hagerman, R.J., Tassone, F., Chudley, A.E., Del Bigio, M.R., Jacquemont, S., Leehey, M. and Hagerman, P.J. (2002) Neuronal intranuclear inclusions in a new cerebellar tremor/ataxia syndrome among fragile X carriers. Brain, 125, 1760–1771.[Abstract/Free Full Text]

34. Brunberg, J.A., Jacquemont, S., Hagerman, R.J., Berry-Kravis, E.M., Grigsby, J., Leehey, M.A., Tassone, F., Brown, W.T., Greco, C.M. and Hagerman, P.J. (2002) Fragile X premutation carriers: characteristic MR imaging findings of adult male patients with progressive cerebellar and cognitive dysfunction. Am. J. Neuroradiol., 23, 1757–1766.[Abstract/Free Full Text]

35. Bontekoe, C.J., Bakker, C.E., Nieuwenhuizen, I.M., van Der Linde, H., Lans, H., de Lange, D., Hirst, M.C. and Oostra, B.A. (2001) Instability of a (CGG)(98) repeat in the Fmr1 promoter. Hum. Mol. Genet., 10, 1693–1699.[Abstract/Free Full Text]

36. Willemsen, R., Hoogeveen-Westerveld, M., Reis, S., Holstege, J., Severijnen, L., Nieuwenhuizen, I., Schrier, M., VanUnen, L., Tassone, F., Hoogeveen, A. et al. (2003) The FMR1 CGG repeat mouse displays ubiquitin-positive intranuclear neuronal inclusions; implications for the cerebellar tremor/ataxia syndrome. Hum. Mol. Genet., 12, 949–959.[Abstract/Free Full Text]

37. Ranum, L.P. and Day, J.W. (2002) Dominantly inherited, non-coding microsatellite expansion disorders. Curr. Opin. Genet. Dev., 12, 266–271.[CrossRef][Web of Science][Medline]

38. Lu, X., Timchenko, N.A. and Timchenko, L.T. (1999) Cardiac elav-type RNA-binding protein (ETR-3) binds to RNA CUG repeats expanded in myotonic dystrophy. Hum. Mol. Genet., 8, 53–60.[Abstract/Free Full Text]

39. Philips, A.V., Timchenko, L.T. and Cooper, T.A. (1998) Disruption of splicing regulated by a CUG-binding protein in myotonic dystrophy. Science, 280, 737–741.[Abstract/Free Full Text]

40. Huang, S., Deerinck, T.J., Ellisman, M.H. and Spector, D.L. (1998) The perinucleolar compartment and transcription. J. Cell. Biol., 143, 35–47.[Abstract/Free Full Text]

41. Michalowski, S., Miller, J.W., Urbinati, C.R., Paliouras, M., Swanson, M.S. and Griffith, J. (1999) Visualization of double-stranded RNAs from the myotonic dystrophy protein kinase gene and interactions with CUG-binding protein. Nucl. Acids Res., 27, 3534–3542.[Abstract/Free Full Text]

42. Tiscornia, G. and Mahadevan, M.S. (2000) Myotonic dystrophy: the role of the CUG triplet repeats in splicing of a novel DMPK exon and altered cytoplasmic DMPK mRNA isoform ratios. Mol. Cell, 5, 959–967.[CrossRef][Web of Science][Medline]

43. Savkur, R.S., Philips, A.V. and Cooper, T.A. (2001) Aberrant regulation of insulin receptor alternative splicing is associated with insulin resistance in myotonic dystrophy. Nat. Genet., 29, 40–47.[CrossRef][Web of Science][Medline]

44. Rosser, T.C., Johnson, T.R. and Warren, S.T. (2002) A cerebellar FMR1 riboCGG binding protein. Am. J. Hum. Genet., 71, 507.

45. Davies, S.W., Turmaine, M., Cozens, B.A., DiFiglia, M., Sharp, A.H., Ross, C.A., Scherzinger, E., Wanker, E.E., Mangiarini, L. and Bates, G.P. (1997) Formation of neuronal intranuclear inclusions underlies the neurological dysfunction in mice transgenic for the HD mutation. Cell, 90, 537–548.[CrossRef][Web of Science][Medline]

46. Petersen, A., Larsen, K.E., Behr, G.G., Romero, N., Przedborski, S., Brundin, P. and Sulzer, D. (2001) Expanded CAG repeats in exon 1 of the Huntington's disease gene stimulate dopamine-mediated striatal neuron autophagy and degeneration. Hum. Mol. Genet., 10, 1243–1254.[Abstract/Free Full Text]

47. Koyano, S., Iwabuchi, K., Yagishita, S., Kuroiwa, Y. and Uchihara, T. (2002) Paradoxical absence of nuclear inclusion in cerebellar Purkinje cells of hereditary ataxias linked to CAG expansion. J. Neurol. Neurosurg. Psychiat., 73, 450–452.[Abstract/Free Full Text]

48. Schmidt, T., Lindenberg, K.S., Krebs, A., Schols, L., Laccone, F., Herms, J., Rechsteiner, M., Riess, O. and Landwehrmeyer, G.B. (2002) Protein surveillance machinery in brains with spinocerebellar ataxia type 3: redistribution and differential recruitment of 26S proteasome subunits and chaperones to neuronal intranuclear inclusions. Ann. Neurol., 51, 302–310.[CrossRef][Web of Science][Medline]

49. Takahashi, J., Fujigasaki, H., Zander, C., El Hachimi, K.H., Stevanin, G., Durr, A., Lebre, A.S., Yvert, G., Trottier, Y., The, H. et al. (2002) Two populations of neuronal intranuclear inclusions in SCA7 differ in size and promyelocytic leukaemia protein content. Brain, 125, 1534–1543.[Abstract/Free Full Text]

50. Calado, A., Tome, F.M., Brais, B., Rouleau, G.A., Kuhn, U., Wahle, E. and Carmo-Fonseca, M. (2000) Nuclear inclusions in oculopharyngeal muscular dystrophy consist of poly(A) binding protein 2 aggregates which sequester poly(A) RNA. Hum. Mol. Genet., 9, 2321–2328.[Abstract/Free Full Text]

51. Saudou, F., Finkbeiner, S., Devys, D. and Greenberg, M.E. (1998) Huntingtin acts in the nucleus to induce apoptosis but death does not correlate with the formation of intranuclear inclusions. Cell, 95, 55–66.[CrossRef][Web of Science][Medline]

52. Perutz, M.F. (1999) Glutamine repeats and neurodegenerative diseases: molecular aspects. Trends Biochem. Sci., 24, 58–63.[CrossRef][Web of Science][Medline]

53. Taylor, J.P., Hardy, J. and Fischbeck, K.H. (2002) Toxic proteins in neurodegenerative disease. Science, 296, 1991–1995.[Abstract/Free Full Text]

54. Watase, K., Weeber, E.J., Xu, B., Antalffy, B., Yuva-Paylor, L., Hashimoto, K., Kano, M., Atkinson, R., Sun, Y., Armstrong, D.L. et al. (2002) A long CAG repeat in the mouse Sca1 locus replicates SCA1 features and reveals the impact of protein solubility on selective neurodegeneration. Neuron, 34, 905–919.[CrossRef][Web of Science][Medline]

55. Bence, N.F., Sampat, R.M. and Kopito, R.R. (2001) Impairment of the ubiquitin–proteasome system by protein aggregation. Science, 292, 1552–1555.[Abstract/Free Full Text]

56. Jana, N.R., Zemskov, E.A., Wang, G. and Nukina, N. (2001) Altered proteasomal function due to the expression of polyglutamine-expanded truncated N-terminal huntingtin induces apoptosis by caspase activation through mitochondrial cytochrome c release. Hum. Mol. Genet., 10, 1049–1059.[Abstract/Free Full Text]

57. Zoghbi, H.Y. and Botas, J. (2002) Mouse and fly models of neurodegeneration. Trends Genet., 18, 463–471.[CrossRef][Web of Science][Medline]

58. Cowan, K.J., Diamond, M.I. and Welch, W.J. (2003) Polyglutamine protein aggregation and toxicity are linked to the cellular stress response. Hum. Mol. Genet., 12, 1377–1391.[Abstract/Free Full Text]

59. Macpherson, J., Waghorn, A., Hammans, S. and Jacobs, P. (2003) Observation of an excess of fragile-X premutations in a population of males referred with spinocerebellar ataxia. Hum. Genet., 112, 619–620.[Web of Science][Medline]

60. Tamanini, F., Bontekoe, C., Bakker, C.E., van Unen, L., Anar, B., Willemsen, R., Yoshida, M., Galjaard, H., Oostra, B.A. and Hoogeveen, A.T. (1999) Different targets for the fragile X-related proteins revealed by their distinct nuclear localizations. Hum. Mol. Genet., 8, 863–869.[Abstract/Free Full Text]

61. Feng, Y., Gutekunst, C.A., Eberhart, D.E., Yi, H., Warren, S.T. and Hersch, S.M. (1997) Fragile X mental retardation protein: nucleocytoplasmic shuttling and association with somatodendritic ribosomes. J. Neurosci., 17, 1539–1547.[Abstract/Free Full Text]

62. Schaeffer, C., Bardoni, B., Mandel, J.L., Ehresmann, B., Ehresmann, C. and Moine, H. (2001) The fragile X mental retardation protein binds specifically to its mRNA via a purine quartet motif. EMBO J., 20, 4803–4813.[CrossRef][Web of Science][Medline]

63. Darnell, J.C., Jensen, K.B., Jin, P., Brown, V., Warren, S.T. and Darnell, R.B. (2001) Fragile X mental retardation protein targets G quartet mRNAs important for neuronal function. Cell, 107, 489–499.[CrossRef][Web of Science][Medline]

64. Sung, Y.J., Conti, J., Currie, J.R., Brown, W.T. and Denman, R.B. (2000) RNAs that interact with the fragile X syndrome RNA binding protein FMRP. Biochem. Biophys. Res. Commun., 275, 973–980.[CrossRef][Web of Science][Medline]

65. Sung, Y.J., Dolzhanskaya, N., Nolin, S.L., Brown, T., Currie, J.R. and Denman, R.B. (2003) The fragile X mental retardation protein FMRP binds elongation factor 1A mRNA and negatively regulates its translation in vivo. J. Biol. Chem., 278, 15669–15678.[Abstract/Free Full Text]

66. Brown, V., Jin, P., Ceman, S., Darnell, J.C., O'Donnell, W.T., Tenenbaum, S.A., Jin, X., Feng, Y., Wilkinson, K.D., Keene, J.D. et al. (2001) Microarray identification of FMRP-associated brain mRNAs and altered mRNA translational profiles in fragile X syndrome. Cell, 107, 477–487.[CrossRef][Web of Science][Medline]

67. Miyashiro, K.Y., Beckel-Mitchener, A., Purk, T.P., Becker, K.G., Barret, T., Liu, L., Carbonetto, S., Weiler, I.J., Greenough, W.T. and Eberwine, J. (2003) RNA cargoes associating with FMRP reveal deficits in cellular functioning in Fmr1 null mice. Neuron, 37, 417–431.[CrossRef][Web of Science][Medline]

68. Zalfa, F., Giorgi, M., Primerano, B., Moro, A., Di Penta, A., Reis, S., Oostra, B. and Bagni, C. (2003) The fragile X syndrome protein FMRP associates with BC1 RNA and regulates the translation of specific mRNAs at synapses. Cell, 112, 317–327.[CrossRef][Web of Science][Medline]

69. Comery, T.A., Harris, J.B., Willems, P.J., Oostra, B.A., Irwin, S.A., Weiler, I.J. and Greenough, W.T. (1997) Abnormal dendritic spines in fragile X knockout mice: Maturation and pruning deficits. Proc. Natl Acad. Sci. USA, 94, 5401–5404.[Abstract/Free Full Text]

70. Irwin, S.A., Patel, B., Idupulapati, M., Harris, J.B., Crisostomo, R.A., Larsen, B.P., Kooy, F., Willems, P.J., Cras, P., Kozlowski, P.B. et al. (2001) Abnormal dendritic spine characteristics in the temporal and visual cortices of patients with fragile-X syndrome: A quantitative examination. Am. J. Med. Genet., 98, 161–167.[CrossRef][Web of Science][Medline]

71. Kleiman, R., Banker, G. and Steward, O. (1994) Development of subcellular mRNA compartmentation in hippocampal neurons in culture. J. Neurosci., 14, 1130–1140.[Abstract]

72. Eberwine, J., Belt, B., Kacharmina, J.E. and Miyashiro, K. (2002) Analysis of subcellularly localized mRNAs using in situ hybridization, mRNA amplification, and expression profiling. Neurochem. Res., 27, 1065–1077.[CrossRef][Web of Science][Medline]

73. Weiler, I.J., Irwin, S.A., Klintsova, A.Y., Spencer, C.M., Brazelton, A.D., Miyashiro, K., Comery, T.A., Patel, B., Eberwine, J. and Greenough, W.T. (1997) Fragile X mental retardation protein is translated near synapses in response to neurotransmitter activation. Proc. Natl Acad. Sci. USA, 94, 5395–5400.[Abstract/Free Full Text]

74. Castren, M., Lampinen, K.E., Miettinen, R., Koponen, E., Sipola, I., Bakker, C.E., Oostra, B.A. and Castren, E. (2002) BDNF regulates the expression of fragile x mental retardation protein mRNA in the hippocampus. Neurobiol. Dis., 11, 221–229.[CrossRef][Web of Science][Medline]

75. Todd, P.K., Malter, J.S. and Mack, K.J. (2003) Whisker stimulation-dependent translation of FMRP in the barrel cortex requires activation of type I metabotropic glutamate receptors. Brain Res. Mol. Brain Res., 110, 267–278.[Medline]

76. Knowles, R.B., Sabry, J.H., Martone, M.E., Deerinck, T.J., Ellisman, M.H., Bassell, G.J. and Kosik, K.S. (1996) Translocation of RNA granules in living neurons. J. Neurosci., 16, 7812–7820.[Abstract/Free Full Text]

77. Bassell, G.J., Oleynikov, Y. and Singer, R.H. (1999) The travels of mRNAs through all cells large and small. FASEB J., 13, 447–454.[Free Full Text]

78. De Diego Otero, Y., Severijnen, L.A., Van Cappellen, G., Schrier, M., Oostra, B. and Willemsen, R. (2002) Transport of fragile X mental retardation protein via granules in neurites of PC12 Cells. Mol. Cell. Biol., 22, 8332–8341.[Abstract/Free Full Text]

79. Kohrmann, M., Luo, M., Kaether, C., DesGroseillers, L., Dotti, C.G. and Kiebler, M.A. (1999) Microtubule-dependent recruitment of Staufen-green fluorescent protein into large RNA-containing granules and subsequent dendritic transport in living hippocampal neurons. Mol. Biol. Cell, 10, 2945–2953.[Abstract/Free Full Text]

80. Zhang, H.L., Singer, R.H. and Bassell, G.J. (1999) Neurotrophin regulation of beta-actin mRNA and protein localization within growth cones. J. Cell Biol., 147, 59–70.[Abstract/Free Full Text]

81. Ainger, K., Avossa, D., Morgan, F., Hill, S.J., Barry, C., Barbarese, E. and Carson, J.H. (1993) Transport and localization of exogenous myelin basic protein mRNA microinjected into oligodendrocytes. J. Cell Biol., 123, 431–441.[Abstract/Free Full Text]

82. Knowles, R.B. and Kosik, K.S. (1997) Neurotrophin-3 signals redistribute RNA in neurons. Proc. Natl Acad. Sci. USA, 94, 14804–14808.[Abstract/Free Full Text]

83. Muslimov, I.A., Santi, E., Homel, P., Perini, S., Higgins, D. and Tiedge, H. (1997) RNA transport in dendrites: a cis-acting targeting element is contained within neuronal BC1 RNA. J. Neurosci., 17, 4722–4733.[Abstract/Free Full Text]

84. Rook, M.S., Lu, M. and Kosik, K.S. (2000) CaMKIIalpha 3' untranslated region-directed mRNA translocation in living neurons: visualization by GFP linkage. J. Neurosci., 20, 6385–6393.[Abstract/Free Full Text]

85. Huber, K.M., Gallagher, S.M., Warren, S.T. and Bear, M.F. (2002) Altered synaptic plasticity in a mouse model of fragile X mental retardation. Proc. Natl Acad. Sci. USA, 99, 7746–7750.[Abstract/Free Full Text]

86. Li, Z., Zhang, Y., Ku, L., Wilkinson, K.D., Warren, S.T. and Feng, Y. (2001) The fragile X mental retardation protein inhibits translation via interacting with mRNA. Nucl. Acids Res., 29, 2276–2283.[Abstract/Free Full Text]

87. Snyder, E.M., Philpot, B.D., Huber, K.M., Dong, X., Fallon, J.R. and Bear, M.F. (2001) Internalization of ionotropic glutamate receptors in response to mGluR activation. Nat. Neurosci., 4, 1079–1085.[CrossRef][Web of Science][Medline]

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