Fig. 7

fgf20a Is Required for Inhibition of Neurogenesis in Segment Centers
(A–L) In situ hybridizations of wt (A–F) or fgf20a homozygous embryos (G–L) raised at 25°C. A′–L′ show higher-power images of A–L. Scale bar, 50 μm for A–L; 20 μm for A′)–(L′. erm expression in segment centers is significantly reduced in fgf20a mutants (open arrowheads in G′). Markers of segment centers, sox9b, cyp26b1, and fgfr2, are greatly decreased in fgf20a^-/- embryos (open arrowheads [H′–J′]). (K and L) fgf20a mutant embryos have ectopic neurogenesis in segment centers, detected by neurog1 (E and K) and neurod4 expression (L and F). Red arrowheads indicate ectopic neurogenesis in segment centers (K′ and L′).
(M and N) Model of the patterning of neurogenesis by fgf20a in hindbrain segments. In wt embryos (M), fgf20a secreted from neurons in the adjacent mantle region (red ovals) prevents neuronal differentiation (blue circles) in segment centers by maintaining a population of progenitors (yellow circles). (N) In fgf20a mutants, there is ectopic neurogenesis and low-level expression of segment center markers.
(O) Summary of the regulation of genes in the nonneurogenic zone of progenitors in segment centers. fgf20a upregulates a set of genes that control different aspects of maintaining an undifferentiated population.