Human Molecular Genetics Advance Access published online on April 6, 2006
Human Molecular Genetics, doi:10.1093/hmg/ddl084
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1 Department of Molecular Genetics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461
* To whom correspondence should be addressed. Most 22q11.2 deletion syndrome (22q11DS) patients have middle and outer ear anomalies while some have inner ear malformations. Tbx1, a gene hemizygously deleted in 22q11DS patients and required for ear development, is expressed in multiple tissues during embryogenesis. To determine the role of Tbx1 in the first pharyngeal pouch (PP I) in forming outer and middle ears, we tissue-specifically inactivated the gene using Foxg1-Cre. In the conditional mutants, PP I failed to outgrow, preventing the middle ear bone condensations from forming. Tbx1 was also inactivated in the otic vesicle (OV), resulting in failure of inner ear sensory organ formation, and in duplication of the cochleovestibular ganglion (CVG). Consistent with the anatomical defects, the sensory genes, Otx1 and Bmp4 were downregulated, while the CVG genes, Fgf3 and NeuroD, were upregulated. To delineate Tbx1 cell-autonomous roles a more selective ablation, exclusively in the OV, was performed using Pax2-Cre. In contrast to the Foxg1-Cre mutants, Pax2-Cre conditional mutant mice survived to adulthood and had normal outer and middle ears but had the same inner ear defects as the Tbx1 null mice, with the same gene expression changes. These results demonstrate that Tbx1 has non-cell autonomous roles in PPI in formation of outer and middle ears and cell-autonomous roles in the OV. Periotic mesenchymal markers, Prx2 and Brn4 were normal in both conditional mutants while they were diminished in Tbx1 -/- embryos. Thus, Tbx1 in the surrounding mesenchyme in both sets of conditional mutants cannot suppress the defects in the OV that occur in the null mutants.
Received February 3, 2006
Revised March 26, 2006
Accepted March 26, 2006
Article
Tissue specific roles of Tbx1 in the development of the outer, middle and inner ear, defective in 22q11DS patients
Jelena S. Arnold 1,
Evan M. Braunstein 1,
Takahiro Ohyama 2,
Andrew K. Groves 3,
Joe C. Adams 4,
M. Christian Brown 5,
and
Bernice E. Morrow 1 *
2 Department of Cell and Molecular Biology, House Ear Institute, 2100 West 3rd Street, Los Angeles, CA 90057
3 Department of Cell and Molecular Biology, House Ear Institute, 2100 West 3rd Street, Los Angeles, CA 90057
4 Department of Otoimmunochemistry, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114
5 Eaton Peabody Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114
Bernice E. Morrow, E-mail: morrow{at}aecom.yu.edu
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