Fig. 9. Summary and model. During A/P patterning of the hypothalamus (16-22 hpf), lef1 and wnt8b are expressed in posterior regions. Later, when neurogenesis begins in the posterior hypothalamus (22-30 hpf), lef1 is required for the expression of sox3, which in turn regulates proneural and neuronal gene expression. After 30 hpf, a specific population of Lef1-dependent neurons differentiates in this region. Morphology of the hypothalamus is adapted from Hauptmann and Gerster (Hauptmann and Gerster, 2000).