Figure 3.

Double-nucleoside labeling demonstrates that the niche cells are not self-renewing. Crayfish were incubated for 24 h in BrdU (red), then maintained in pond water for 7 days. Six hours before sacrifice, they were treated with EdU (green). Brains also were labeled immunocytochemically for glutamine synthetase (blue) to reveal the niche and streams. (A) BrdU+ cells were found only in the proliferation zones (MPZ and LPZ), not in the niche. Only EdU labels S-phase cells in the niche, showing that niche cells do not retain BrdU, and thus that divisions are not self-renewing. These labeling patterns also demonstrate that migration is unidirectional, away from the niche. (B) Higher magnification image of the LPZ. Arrow in B indicates the direction of neural precursor cell migration. Scale bars: (A), 100 μm; (B), 50 μm. Adapted from Benton et al. (2014).