Functional conservation of atonal and Math1 in the CNS and PNS

To determine the extent to which atonal and its mouse homolog Math1 exhibit functional conservation, we inserted beta-galactosidase (lacZ) into the Ma th1 locus and analyzed its expression, evaluated consequences of loss of Ma th1 function, and expressed Math1 in atonal mutant flies. lacZ under the co ntrol of Math1 regulatory elements duplicated the previously known expressi on pattern of Math1 in the CNS (i.e., the neural tube, dorsal spinal cord, brainstem, and cerebellar external granule neurons) but also revealed new s ites of expression: PNS mechanoreceptors (inner ear hair cells and Merkel c ells) and articular chondrocytes. Expressing Math1 induced ectopic chordoto nal organs (CHOs) in wild-type flies and partially rescued CHO loss in aton al mutant embryos. These data demonstrate that both the mouse and fly homol ogs encode lineage identity information and, more interestingly, that some of the cells dependent on this information serve similar mechanoreceptor fu nctions.