Human Molecular Genetics Advance Access published online on December 24, 2007
Human Molecular Genetics, doi:10.1093/hmg/ddm373
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Differential aggregation and functional impairment induced by polyalanine expansions in FOXL2, a transcription factor involved in cranio-facial and ovarian development.
1 INSERM U567, Team21 "Genomics and Epigenetics of Placental Diseases", Genetics and Development Department, Institut Cochin, 24 rue du Faubourg St-Jacques, 75014, Paris, France 2 CNRS UMR8104, Institut Cochin, 24 rue du Faubourg St-Jacques, 75014, Paris, France 3 Université Paris Descartes, Faculté de Médecine Cochin-Port-Royal, 24 rue du Faubourg St-Jacques, 75014, Paris, France 4 INRA-BDR, Jouy en Josas 5 Université Denis Diderot, Paris VII, Paris, France.
* Correspondence to : veitia{at}cochin.inserm.fr, Équipe 21. Institut Cochin. Faculté de Médecine. 24 rue du Faubourg Saint Jacques. 75014 Paris
Received November 26, 2007; Revised December 19, 2007; Accepted December 19, 2007
Polyalanine (polyAla) tract expansions have been associated with an increasing number of human diseases. Here, we have undertaken a functional study of the effects of polyAla expansions in the context of the transcription factor FOXL2, involved in cranio-facial and ovarian development. Using two cellular models, we show that FOXL2 polyAla expansions lead to protein mislocalisation and aggregation in a length-dependent manner. The fraction of cells containing cytoplasmic staining displays a sigmoidal relationship with respect to the length of the polyAla tract, suggesting the existence of a threshold length above which protein mislocalisation occurs. The existence of such a threshold might be rationalised if we consider that the longer the polyAla tract is, the higher its tendency to misfolding or to inducing spurious interactions with cytoplasmic components. To study the intranuclear dynamics of polyAla-expanded FOXL2, we performed Fluorescence Recovery After Photobleaching (FRAP) experiments. The most unexpected result concerned the pathogenic protein containing 19 Ala residues in the run, which was virtually immobile, although this variant does not present a classical aggregation pattern. Luciferase assays and real time RT-PCR of many target genes showed that polyAla expansions induce different losses of activity according to the target promoters tested. We provide molecular explanations for these findings. Although our main focus is the mechanisms of pathogenesis of polyAla-expanded proteins, we discuss the potential relevance of polyAla length variation in micro- and macroevolution because polyAla-containing proteins tend to be transcription factors.
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