F-Spondin Expression in Zebrafish Figure 6. Spon1b expression in thalamic and pretectal regions. A. Horizontal section showing spon1b mRNA-positive nuclei (in situ hybridization): dorsoposterior (DP), centroposterior (CP) and ventrolateral (Vl) thalamic nuclei; anterior parvocellular preoptic (Ppa); Ventral Tel (Vv). B. Coronal section through the thalamus, immunostained for GFP. Medial (PGm) and lateral (PGl) preglomerular nuclei, torus longitudinalis (TL), ventral hypothalamus (Hv), optic tectum (TeO). C. Periventricular region (boxed area in B in adjacent section), showing spon1b-positive cells in the dorsal (PPd) and ventral (PPv) periventricular pretectal nuclei, in the posterior tuberculum (TPp), in the posterior tuberal nucleus (PTN) and in fibers of the fasciculus retroflexus (FR). Note absence of signal in the subcommissural organ (asterisk: SCO region, ventral to posterior commissure, Cpost). Scale bars: A-B: 100 mm; C: 50 mm. doi:10.1371/journal.pone.0037593.g006 In the habenular neurogenic niche, the majority of BrdU- positive cells were located along the midline, adjacent to the diencephalic ventricle and vHb. In some specimens, the Hb niche extended ventrally, merging with the ventral thalamic niche. We observed a distinct rostro-caudal organization of the Hb niche, 2 hours post-BrdU injection. At the most rostral levels, the BrdU- positive cell nuclei were found immediately ventral to the vHb (Fig. 10C). More caudally, the dividing cells were concentrated in the medio-dorsal region of the vHb (Fig. 10D). Thereafter, at the level of the habenular commmissure (cHb), BrdU-positive nuclei again were located medio-ventral to the vHb nuclei (Fig. 10E). At all levels, few BrdU cells could be observed within the parenchyma of the Hb at 2 hours post-injection (Fig. 10C-E). Four days after BrdU incorporation, the newly-divided cells could be found close to the periphery of the Hb niche, migrating dorsally along the ventricular walls and into the ventral and dorsal Hb (Fig. 10F). At 1 month post-injection, the surviving BrdU- labeled cells could not be detected in the niche per se, but were localized in the ventral and dorsal Hb nuclei (Fig. 10G-H). Over a 2-month post-injection period, most of the BrdU-labeled cells moved into the dHb nuclei (Fig. 10I). Importantly, none of the PLoS ONE | www.plosone.org 10 June 2012 | Volume 7 | Issue 6 | e37593