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Fig. S15 A central DeltaD-positive cell is established at the center of maturing neuromasts. (A) ZO1 is recruited to the center (white arrowheads) of maturing proneuromasts in the pLLp and in deposited neuromasts. Morphogenesis of epithelial rosettes can be followed by examining the progressive accumulation of Cldnb at the center (white arrowheads) of maturing proneuromasts. (B) A single central cell with multiple vesicles of DeltaD protein is seen at the center of the maturing epithelial rosettes. Expression of DeltaD in a single cell becomes apparent prior to obvious epithelial rosette formation, as indicated by central accumulation of Cldnb (white arrowheads). Embryos were immunostained with anti-ZO1 (green) in A and with anti-DeltaD monoclonal antibody (green) in B; Cldnb was visualized with anti-Cldnb polyclonal antibody (red). Each prospective proneuromast domain is indicated by white brackets. (C) Schematic showing central accumulation of ZO1 as epithelial rosettes mature. As the central cell expresses atoh1a and becomes a sensory hair cell precursor, it also becomes the source of DeltaD and fgf10, while neighboring cells that express fgfr1 are maintained as progenitors and become supporting cells.