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Fig. 8 Etv5b is required to keep 5-HT progenitors in a proliferative state and to maintain the pool of 5-HT progenitors. (A) The procedure for analysis of fate at 72 hpf of hypothalamic 5-HT progenitors labelled with BrdU at 36 or 45 hpf. (B) The proportion of 5-HT/BrdU double-positive cells among 5-HT-positive cells in the intermediate/posterior (i./p.) clusters at 72 hpf after a single BrdU pulse at 36 or 45 hpf expressed as percentage of control. These observations suggest that the 5-HT progenitor population, following a transient cell cycle delay, is depleted in etv5b morphants, resulting in an overall decrease in the number of 5-HT neurons at 72 hpf. n, total number of embryos analysed for each experiment. *Pd0.05. (C-N) Confocal optical sections of coronal cryosections from etv5b morphants or uninjected controls. Both were exposed to a single pulse of BrdU at 36 (C-H) or 45 (I-N) hpf and processed for BrdU and 5-HT double immunohistochemistry at 72 hpf. Sections are at the level of the i./p. cluster of 5-HT cells of the hypothalamus. Arrows indicate examples of double-positive cells. Scale bar: 25 μm.