Fig. 6. Immunolocalization of Nowa protein in dividing nematoblasts. (A) The nematocyte differentiation pathway in Hydra. Nematocytes originate from interstitial stem cells (I-cells), which divide three- to five-times after commitment (nematoblasts) and remain interconnected by cytoplasmic bridges forming nests of 8-32 cells (David and Challoner, 1974; David and Gierer, 1974). After nematocytes have formed a nematocyst (green), nests brake up into single nematocytes, which migrate to the tentacles. (B-D) Confocal microscopy of mAb H22 (green) in dividing nematoblasts. (B) Nematoblast nest in metaphase (optical section) with nuclei (blue) in metaphase condensation numbered 1-8. One of the mAb-H22-positive capsule primordia is indicated by an arrow. (C) Surface projection of the same nest, the boundary of the nest is indicated by a dotted line. (D) Nematoblast in division with metaphase spindle apparatus visualized by mAb anti-tubulin (red). Projections from different angles show the asymmetrical position of the capsule primordium. (E) Continuous [³H]thymidine labeling of mAb-H22-positive nests. The first labeled nests appeared 5 hours after onset of labelling; values represent single measurements from two independent experiments. Bars, 5 µm.