In the April 28th online edition of PNAS, L. M. Friedman et al. from the Univ. of Washington reported their study results on the role of microRNAs in the development of mouse cochlea and vestibule of the inner ear. The study consisted of demonstrating that in conditional knock-out mouse for Dicer1, miRNAs were crcucial for inner ear development and postnatal survival of functional hair cells. Microarray analysis revealed that six miRNAs (miR-15a, miR-18a, miR-30b, miR-99a, miR-182, and miR-199a) were temporally and spatially expressed in the newborn-mouse cochleae and vestibules. In the zebrafish, expression of miR-15a and miR-18a were shown to be critical for inner ear development and morphogenesis. Specifically, miR-15a may target mRNAs for Sic12a2, Cldn12, and Bdnf. The authors concluded that their data "support the hypothesis that inner ear tissue differentiation and maintenance are regulated and controlled by conserved sets of cell-specific miRNAs in both mouse and zebrafish."