Figure 1.

Characterizing normal OT neurogenic growth in 5–16 dpf zebrafish larvae. From 10 to 16 dpf, the volume of the tectal neuropil increases (A), whereas the Hoechst⁺ cell density in the tectal neuropil remains the same (B). C, Dorsal, horizontal schematic of a larval brain, indicating locations of the OT neuropil, PGZ, and the coronal plane along which the tectum was sectioned (red line referring to the location of sections in a 5 dpf (Di) and 16 dpf (Dii) larvae below). Scale bar, 20 μm. New tectal cells are generated in the mediodorsal and ventrolateral PGZ, as visualized by EdU⁺ labeling (E). Scale bar, 30 μm. A radial glial stem cell population, as visualized by expression of her4.1:mCherry enhanced using immunohistochemistry with a DsRed antibody that cross-reacts with mCherry, in the OT exists across the ventral and medial boundaries of PGZ and appear overwhelmingly quiescent, with only few mCherry⁺ cells incorporating EdU in the medial neurogenic niche (Ei–Eiii). Scale bar, 30 μm. Proliferative activity in the OT according to expression of ccnd1 concurs with our EdU⁺ data, in that proliferation is limited to medial and lateral niche flanking the tectal neuropil (F) that meet dorsally in the caudalmost PGZ, beyond the neuropil (G). Scale bar, 30 μm. New tectal neurons born on 5 dpf (Hi) appear to displace into the PGZ by 10 (Hii) and 16 dpf (Hiii). Scale bar, 15 μm. Displacement of EdU⁺ cells from 5 to 16 dpf quantified for the medial and lateral niches in I and J, respectively. Within the medial and lateral neurogenic niches, most new neurons are generated in the caudal third compared with the middle and rostral third (K and L, respectively). Cell proliferation rates decrease from 5 to 16 dpf in the medial (M) and lateral (N) neurogenic niches. Lines indicate mean ± SEM. *p < 0.05.