09-P099 Shifting of borders between cells of ectoderm and endoderm during mouth formation in the Mexican axolotl

The inner ear develops from a simple epithelial vesicle that gives rise to the sensory hair cells, neuroblasts, secretory cells and other non-sensory tissue of the inner ear. In the zebrafish embryo, sensory hair cells begin to differentiate at the anterior and posterior ends of the otic vesicle, forming two distinct and separate sensory patches or maculae. Otic neuroblasts arise from an anteroventral region of the epithelium between the two maculae, and subsequently delaminate and coalesce to form the statoacoustic ganglion beneath the ear. We are examining the roles of various transcription factors in patterning ventral regions of the zebrafish otic epithelium. We show that eya1/six1, tbx1 and otx1 regulate the spatial extent of the neurogenic domain in the otic vesicle and are required for the correct spacing of the sensory patches. In the vgo/tbx1 mutant and otx1 morphant at 26–27 h post-fertilisation, expression of otx1-like and gsc is lost in the otic vesicle, sensory patch spacing is reduced, the neurogenic domain expands laterally, and the developing statoacoustic ganglion is enlarged. In contrast, dog/eya1 mutants and six1 morphants show a reciprocal phenotype: expression of tbx1, otx1, otx1-like and gsc in the otic vesicle is expanded, sensory patch spacing is increased, and neurogenesis is severely suppressed. We will discuss the regulatory interactions between these transcription factors and their requirements in patterning ventral regions of the zebrafish otic epithelium.