Spatial-Temporal Regulation of the Atonal Homolog 1 Gene
Adams, Chris Aries
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Controlled spatio-temporal expression of atonal homolog 1 is necessary for the correct development of the cerebellar granule cells, the dorsal interneuron 1 population, gut goblet cells and the cochlear and vestibular hair cells of mice. The purpose of these studies was to determine how atonal homolog 1 is regulated by analyzing the activity of atonal homolog 1 regulatory regions. This was accomplished by deleting different conserved regions in a bacterial artificial chromosome (318GFPBAC) containing ~180 kb of sequence 5' and 3' of atonal homolog 1 and assaying for green fluorescent protein expression in transgenic mice. Transgenic embryos were analyzed at embryonic day 10.5 in the neural tube, metencephalon and rhombencephalon and at embryonic day 16.5 in merkel cells, inner ear cells, vestibular cells and the cerebellum all tissues where endogenous atonal homolog 1 is expressed. Auto-regulation from an enhancer region 3' of the atonal homolog 1 gene (enhancer AB) was previously shown to be sufficient for atonal homolog 1-specific expression. In this paper, I show that enhancer AB is required for expression from the 318GFPBAC indicating that there are no other auto-regulatory elements for atonal homolog 1 expression in the 200 kb tested. Further, I have located an evolutionarily conserved region that has not previously been tested 12 kb 3' of the atonal homolog 1 coding region (enhancer C). When enhancer C is deleted from the 318GFPBAC, green fluorescent protein expression is not affected at embryonic day 10.5 or embryonic day 16.5. Also, enhancer C cannot drive green fluorescent protein expression by itself at embryonic day 10.5 or embryonic day 16.5. Thus no role for this conserved sequence around atonal homolog 1 was detected in these studies. To date, the AB enhancer is the only sequence shown in vivo to function in atonal homolog 1 regulation being both necessary and sufficient to direct expression in an atonal homolog 1 pattern.