Mammalian inner ear development begins with the induction of the otic placode, an ectodermal thickening on either side of the hindbrain. Placode invagination forms the otic vesicle, which differentiates into the inner ear. Many genes are involved in this developmental program but their function during inner ear morphogenesis is poorly understood. On p. 3989, Zheng et al. investigate the role of the mammalian homeobox gene Six1 in auditory system development. They report that Six1 is expressed in all the sensory epithelia of the developing ear in normal mice. By examining auditory system development in Six1-/- mice, they also show that Six1, similar to Eya1, is not required for initiation of inner ear organogenesis but rather regulates important signalling molecules(including Fgf3, Fgf10 and Bmp4) that are involved in the specification of the inner ear sensory organs.

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