Molecular characterization and mapping of ATOH7, a human atonal homolog with a predicted role in retinal ganglion cell development

Abstract

The human ATOH7 gene encodes a basic helix-loop-helix (bHLH) transcription factor that is highly similar to Drosophila Atonal within the conserved bHLH domain. The ATOH7 coding region is contained within a single exon. We mapped ATOH7 to Chromosome (Chr) 10q21.3-22.1, a region syntenic to the segment of mouse Chr 10 where Atoh7 (formerly Math5) is located. The evolutionary relationship between ATOH7 and other atonal homologs was investigated using parsimony analysis. A direct comparison of ATH5/7 and ATH1 protein subgroups to Atonal also revealed a nonrandom distribution of amino acid changes across the bHLH domain, which may be related to their separate visual and proprioceptive sensory functions. Among bHLH genes, ATOH7 is most closely related to Atoh7. This sequence conservation extends significantly beyond the coding region. We define blocks of strong homology in flanking human and mouse genomic DNA, which are likely to include cis regulatory elements. Because targeted deletion of Atoh7 causes optic nerve agenesis in mice, we propose ATOH7 as a candidate for human optic nerve aplasia and related clinical syndromes.Early development of the mammalian retina proceeds through a series of cell fate decisions in which progenitor cells in the optic cup progressively exit mitosis, migrate to specific laminar positions, and terminally differentiate into one of seven basic neural or glial cell types. Defects in retinal cell determination or differentiation lead to specific malformations in humans, including Leber's congenital amaurosis (Freund et al. 1998;Sohocki et al. 1998), cone-rod dystrophy (Freund et al. 1997;Sohocki et al. 1998;Swain et al. 1997), enhanced S-cone syndrome (Cepko 2000;Haider et al. 2000), and optic nerve aplasia or hypoplasia (Lee et al. 1996;Scott et al. 1997;Weiter et al. 1977). Although the genetic basis for retinal histogenesis is poorly understood, recent findings suggest that key proteins controlling some of these developmental processes are nuclear transcription factors Freund et al. 1997;Kobayashi et al. 1999;Swain et al. 1997;Wang et al. 2001).Basic helix-loop-helix (bHLH) transcription factors regulate multiple aspects of retinal neuron formation in vertebrates and invertebrates Vetter and Brown 2001;Cepko 1999). Proneural bHLH proteins contain basic DNA-binding and helix-loop-helix dimerization Correspondence to: T. Glaser; E-mail: tglaser@umich.edu. The nucleotide sequence data reported in this paper have been submitted to GenBank and assigned the accession numbers AF418922 and AF418923. (Jarman et al. 1993). While several vertebrate atonal homologs (Atoh proteins) have been identified, most act only during peripheral or central nervous system development and are not expressed significantly during eye formation. In contrast, the ATH5/7 subclass (named for Xenopus Xath5 and mouse Atoh7) is highly expressed by retinal progenitors during the early stages of eye development in zebrafish, chick, frog, and mouse (Brown et al. 1998;Kanekar et al. 1997;Liu et al. 2001;Masai et al. 2...

Conserved regulation of Math5 and Math1 revealed by Math5-GFP transgenes

“…In the upstream region of Math5, two highly conserved regions among the Xenopus, mouse and human Ath5 genes are shown (yellow boxes in Fig. 7A) (Brown et al, 2002;Hutcheson et al, 2005;Riesenberg et al, 2007). Within these two evolutionarily conserved regions are four E-boxes, bHLH consensus binding sites (blue boxes) (Murre et al, 1989;Hutcheson et al, 2005).…”

bHLH-dependent and -independent modes ofAth5gene regulation during retinal development

“…Other vertebrate Ath5 genomic sequences were identified as follows: X. tropicalis (http://genome.jgi-psf.org/xenopus0/ xenopus0.home.html); mouse and human Ath5 (Atoh7) have been previously isolated and aligned (Brown et al, 2002); chick (GenBank Number AJ630209) (Skowronska-Krawczyk et al, 2004); Fugu (scaffold 1775; http://genome.jgi-sf.org/fugu3/fugu3.home.html); and zebrafish (clone AL627094; http://trace.ensembl.org/perl/ssahaview). The genomic sequence for Drosophila atonal was derived from BAC clone #AC008094 (http://flybase.bio.indiana.edu/).…”

A bHLH transcriptional network regulating the specification of retinal ganglion cells

“…The cloned sequence accurately reproduces the activity and the mode of regulation of the endogenous promoter. It contains essential regulatory elements that are well conserved across distant vertebrate species (Brown et al, 2002;Hutcheson et al, 2005;Skowronska-Krawczyk et al, 2004), but it is unclear whether the different species use similar strategies to regulate ATH5 expression. Whereas a proximal cis-regulatory region of the Xenopus Xath5 gene suffices, much as in the chick retina, to drive retina specific reporter gene expression in a bHLHdependent manner, the mouse ATH5 promoter appears to be regulated differently (Hutcheson et al, 2005).…”

“…Initially cloned and analysed in Xenopus (Kanekar et al, 1997), its mouse (Brown et al, 1998), zebrafish (Masai et al, 2000), chicken (Liu et al, 2001;Matter-Sadzinski et al, 2001) and human (Brown et al, 2002) orthologues have also been identified. In the mouse, In the developing retina, the production of ganglion cells is dependent on the proneural proteins NGN2 and ATH5, whose activities define stages along the pathway converting progenitors into newborn neurons.…”