Atoh1 is required for the formation of lateral line electroreceptors and hair cells, whereas Foxg1 represses an electrosensory fate

In electroreceptive jawed fishes and amphibians, individual lateral line placodes form lines of neuromasts on the head containing mechanosensory hair cells, flanked by fields of ampullary organs containing electroreceptors - modified hair cells that respond to weak electric fields. Extensively shared gene expression suggests that conserved molecular mechanisms are involved in their development, but a few transcription factor genes are restricted either to the developing electrosensory or mechanosensory lateral line. Here, we used CRISPR/Cas9-mediated mutagenesis in F0-injected sterlet embryos (Acipenser ruthenus, a sturgeon) to test the function of three such genes. We found that the ‘hair cell’ transcription factor geneAtoh1is required for both hair cell and electroreceptor differentiation in sterlet, and forPou4f3andGfi1expression in both neuromasts and ampullary organs. These data support the conservation of developmental mechanisms between hair cells and electroreceptors. Targeting ampullary organ-restrictedNeurod4did not yield any phenotype, potentially owing to redundancy with otherNeurodgenes that we found to be expressed in sterlet ampullary organs. After targeting mechanosensory-restrictedFoxg1, ampullary organs formed within neuromast lines, suggesting that Foxg1 normally represses their development. We speculate that electrosensory organs may be the ‘default’ fate of lateral line primordia in electroreceptive vertebrates.