Figure 2. Stem cells exhibit class-specific spatial and temporal patterns during intramolluscan development.

(A) FISH of nanos-2 and fgfrA reveals spatial distributions of cell classes in a mother sporocyst containing daughter embryos (dashed circles), 10 days post-infection (dpi). sWGA (grey) labels the parasite surface (tegument). Arrows: extraembryonic κ-cells. Right: rendered image of that shown to the left. Spheres: cell centers; yellow arrowheads: ϕ-cells beneath the surface. (B) Mature daughter sporocysts contained in a mother sporocyst 15 dpi. Dashes outline the body surfaces of daughters. In daughters, κ-cells comprised 522 out of 592 counted stem cells in these daughters, while fewer δ-cells (61/592) and φ-cells (9/592) were observed. (C) Daughter sporocysts in snail ovotestis, 25 dpi. (D) Early cercarial embryo before the tail bud forms. φ-cells were found concentrated both anteriorly and posteriorly, where the mouth and tail bud form; only two κ-cells were detected posterior to the two penetration glands. (E) Later development during cercarial embryogenesis. φ-cells were mostly located in the tails; the κ-cell pair were posterior to the glands. (F) Mature cercarial body in daughter sporocysts 30 dpi (dorsal view). 1: anterior midline cell; 2L, 2R: anterior lateral cells; 3L, 3R: posterior lateral cells. Arrowheads: κ-cells, asterisks: ϕ-cells, arrows: δ-cells. sWGA: penetration glands. Note that only the cercarial body is transmitted to the mammalian host, whereas tails are discarded outside of the host epidermis during penetration. (G) κ-cell clusters, magnified from (F), contain multiple cells each (single confocal section). Arrows: individual nuclei in κ-cell clusters. Scale bars: 20 µm. All images are maximum intensity projections from 30 µm tissue cryosections. Since animals are thicker than the sections, parasite surface and penetration glands were used to determine the orientation and position of the sections.