title: The role of bHLH genes in ear development and evolution: revisiting a 10-year-old hypothesis.
abstract: In mouse ear development, two bHLH genes, Atoh1 and Neurog1, are essential for hair cell and sensory neuron differentiation. Evolution converted the original simple atonal-dependent neurosensory cell formation program of diploblasts into the derived developmental program of vertebrates that generates two neurosensory cell types, the sensory neuron and the sensory hair cell. This transformation was achieved through gene multiplication in ancestral triploblasts resulting in the expansion of the atonal bHLH gene family. Novel genes of the Neurogenin and NeuroD families are upregulated prior to the expression of Atoh1. Recent data suggest that NeuroD and Neurogenin were lost or their function in neuronal specification reduced in flies, thus changing our perception of the evolution of these genes. This sequence of expression changes was accompanied by modification of the E-box binding sites of these genes to regulate different downstream genes and to form inhibitory loops among each other, thus fine-tuning expression transitions.
authors.affiliation: Department of Biology, College of Liberal Arts and Sciences, University of Iowa, 143 BB, Iowa City, IA 52242, USA. bernd-fritzsch@uiowa.edu
authors.forename: Bernd
authors.initials: B
authors.lastname: Fritzsch
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Eberl
authors.forename: Kirk W
authors.initials: KW
authors.lastname: Beisel
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000502:physiology*; D002454:Cell Differentiation / Q000235:genetics*; D007758:Ear, Inner / Q000254:growth & development*; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D051379:Mice; D009024:Morphogenesis / Q000235:genetics*; D011984:Sensory Receptor Cells / Q000166:cytology / Q000502:physiology*; D013234:Stem Cells / Q000166:cytology / Q000502:physiology
chemical_list: D051792:Basic Helix-Loop-Helix Proteins