Transcription factor that binds a palindromic (canonical) core consensus DNA sequence 5'-CANNTG- 3' known as an E-box element, possibly as a heterodimer with other bHLH proteins (By similarity). During development, is required for heart looping and swim bladder formation by acting in concert with GATA4 AND ZFPM1 (PubMed:23836893). During the development of both the retina and skeletal muscles is required for neural retinal cell through modulating PAX6 and NEUROG3 expression and myogenic differentiation (PubMed:20532172). Weakly expressed in the heart tube at 30 hours post-fertilization (PubMed:23836893). Expressed at as early as epiboly stage, and is broadly distributed till early segmentation stage and in developing retina and skeletal muscle. In the eye, expression is detected in the optic primordium at the 6-somite stage and is steadily expressed during the invagination of the optic vesicle from its initiation to its expansion to the lens rudiment. In skeletal muscle, a faint signal is detected in muscle precursor cells at the early segmentation period, and in ventral somites from the 21-somite to 24 hour post fertilization stage. Expression decreases sharply during 36 to 48 hour post fertilization stage while it reached its highest level at about 72 hour post fertilization stage. During this period, the distribution extends to the dorsal somites. In addition also appeared in the brain and neural crest cell (PubMed:20532172). Morpholino knockdown of atoh8 causes two phenotypes. The severe phenotype displays a shrunken head, reduced eye size and fused somites and most embryos die within 3 days. The mild phenotype displays an abnormal brain shape with smaller eyes, a curved body axis with indistinct somite boundaries and frequently reduced or no circulation. In addition, the yolk extension is hardly visible starting at the beginning of tail straightening from the 17-somite stage. Contains a degenerate basic motif not likely to bind DNA.