Analysis of gene expression profiles along the tonotopic map of mouse cochlea by cDNA microarrays.

Conclusion: This study demonstrated differential gene expression profiles along the axis of the mouse cochlea. It also suggests the mechanism that establishes the tonotopic organization.

Objectives: The molecular basis of the tonotopic mapping of the mammalian cochlea remains unclear. We therefore examined the genes that were abundantly expressed in either the apex or the base of mouse cochlea.

Materials and methods: Apical and basal portions of cochlea, which contained the organ of Corti and spiral ganglion neurons, were independently dissected from 10 adult C57BL/6 mice, and their total RNAs were respectively isolated. The gene expression profiles of each of these two pools were examined and compared to each other by the complementary DNA microarray technique.

Results: Of 20,289 probes tested, 64 genes were found to be expressed in the apical portion more than fivefold more abundantly than in the basal portion, and 77 genes were vice versa. Of interest, the genes of several functional proteins such as beta2- and gamma2-subunits of GABA(A) receptors dominated the basal part, indicating that these molecules may be involved in high-frequency tuning of the hair cells and/or ganglion neurons.