Neuronal differentiation (Hu-protein) and complementarity of bHLH gene expression (neuroD=nrd and Zash-1a) in the 3-dpf zebrafish brain. Levels shown are: olfactory bulb (A1–3), precommissural telencephalon (B1–3), supracommissural telencephalon (C1–3), ventral thalamus/preoptic region (D1–4); note that PCNA-positive cells are additionally shown for this level in D4 and that these proliferative cells are perfectly complementary to differentiating Hu-positive cells shown in D3), hypothalamus (E1–2,F1–3), cerebellar plate (G1–2). Abbreviations: ac, anterior commissure; CeP, cerebellar plate; DT, dorsal thalamus; E, epiphysis; EGL, external granular layer; EPi, eye pigment; Ha, habenula; Hi, Hr intermediate, rostral hypothalamic zones; Hy; hypophysis (pituitary); MO, medulla oblongata; M1, migrated pretectal region; M2, migrated posterior tubercular (preglomerular) region; OB, olfactory bulb; OE, olfactory epithelium; P, pallium; Pi, meningeal pigment; Po, preoptic area; PTv, ventral part of posterior tubercle; S, subpallium; Sd, dorsal subpallium; Sv, ventral subpallium; TeO, optic tectum; VCP, ventral cerebellar proliferation; VT, ventral thalamus; ZI, zona limitans intrathalamica.