Pole cell migration through the gut wall of the Drosophila embryo: analysis of cell interactions.

Early in development the precursors of germ cells in Drosophila migrate at the posterior pole of the embryo and translocate to the bottom of the developing posterior midgut primordium. At the end of germ band elongation the pole cells cross the gut wall to enter in association with the gonadal mesoderm. We used laser scanning confocal microscopy on whole-mount Rh-phalloidin-stained embryos and transmission electron microscopy to investigate how pole cells cross the epithelial wall of the posterior midgut primordium. Our results suggest that pole cells leave the midgut sac by traveling through the intercellular spaces of the epithelium. During this process the epithelial cells at the bottom of the posterior midgut primordium are greatly deformed, but their junctional complexes do not completely release, avoiding breaks in the epithelial wall.