The Irx3 and Irx5 genes in inner ear development

Abstract

Iroquois genes encode a family of highly conserved homeodomain transcription factors across the metazoans that are involved in multiple developing processes. Irx3 and Irx5 are linked in IrxB cluster in mouse and human genome, which are essential in the neurogenesis of ventral neural tube. Preliminary data indicated that Irx3 and Irx5 double mutant mice display significant hearing defect. However, the role of these two genes during inner ear development is poorly characterized. To understand the function of Irx3 and Irx5 during mouse inner ear development, the expression of these two genes in the otic placode and derivatives are examined. Two allelic mouse mutants, Irx3tauLacZ and Irx3flox;Irx5EGFP, which labeled Irx3 and Irx5 by β-gal and EGFP respectively, are analyzed to investigate the expression of these two genes. Irx3 is expressed in the ventral region of otic vesicle at E10.5 and Irx5 is expressed in the prosensory region of the cochlear duct at E12.5. Further experiments are currently conducted to complete the analysis of expression patterns of Irx3 and Irx5 during inner ear development. Previous studies have demonstrated that Irx3 and Irx5 shares strikingly similar expression pattern, which could be explained by enhancer sharing and coregulation. To test this hypothesis, we attempt to identify the cis-regulatory elements of Irx3 and Irx5 which are responsible for inner ear development. Four putative inner ear specific enhancer elements are predicted in the intergenic region between Irx3 and Irx5 (550kb) by phylogenetic anaylsis and transcription factor binding sites prediction. To examine the enhancer activities of these four regions, we have generated construct c1 to c4 with EGFP as a reporter gene and the chick in ovo electroporation assay will be performed. Our data showed that osteoblasts can be reprogrammed to iPS cells with pluripotency potential as shown by their ability to form teratomas and contribute to chimeric embryos. The system will enable us to test the possibility of “capturing” or enriching for osteochondroprogenitors during the reprogramming process.