Fig. 7. A model of the transition from neurogenesis to sensory hair cell formation. (A-A'') Tissue-level changes in Ngn1 expression (cyan), Math1 expression (beige hatching), and regions where Ngn1 expression has been extinguished (dark blue/gray) from E10.5-14.5. Light gray stripe at E11.5 represents Bmp4 expression, which marks the prospective anterior and lateral cristae. pUt, presumptive utricular macula; pSac, presumptive saccular macula; ut m, utricular macula; sac m, saccular macula; ac, anterior crista; lc, lateral crista. (B-B'') Changes in gene expression and behavior (delamination) on a cellular scale and over short periods (denoted by arrows) in the neurogenic region of the otocyst (B), presumptive maculae (B') and definitive maculae (B''). Shades of blue represent various intensities of Ngn1 expression (see key). Beige represents Math1⁺ cells. White represents cells expressing neither bHLH gene (sensory-restricted progenitors) that can differentiate as either hair or supporting cells. (C,C') Genetic interactions (black lines), gene functions (gray lines) and cell fate transformations (red lines) before (C) and after (C') the onset of Math1 expression. Dll1, delta-like 1; N, Notch receptor. Solid gray and black lines indicate cell-autonomous interactions or functions. Dotted gray and black lines indicate non-cell-autonomous interactions or functions. Solid and dotted lines between Ngn1 and Math1 indicate that either, or both, mechanisms might mediate cross-inhibition.