Understanding inner ear development with gene expression profiling.

Understanding the development of the inner ear requires knowing the spatial and temporal pattern of gene expression, and the functions of those gene products. In the last decade, hearing research has benefited tremendously from the progress of the human and mouse genome projects, as amply illustrated by the identification of many deafness genes in both human and mouse. However, the sheer amount of information generated from the genome project has far outpaced the rate at which it is utilized. Microarray technology offers a means to quantify the expression level of transcripts at a whole-genome scale. Cross-tissue comparisons will identify genes unique to the inner ear, which will expedite the identification of new deafness genes. Microdissection and subtraction after ablation of cell types can reveal genes expressed in certain cells, such as hair cells. Expression profiling of both inner ear and other tissues, under a variety of conditions (such as during development, with drug treatment or in knock-out animals), can be used for cluster analysis to group genes of similar expression. Coexpression can suggest functional pathways and interactions between known genes, and can identify new genes in a structure or pathway. In this review we give examples for both transcription factors and cochlear structures.