Lineage analysis of transplanted individual cells in embryos of Drosophila melanogaster : II. Commitment and proliferative capabilities of neural and epidermal cell progenitors.

Some aspects of neural and epidermal cell lineages during embryogenesis of Drosophila melanogaster were studied by transplanting horseradish-peroxidase-(HRP-) labelled ectodermal cells from young gastrula donors into host embryos of similar ages. Heterotopic transplantations permitted us to assess the degree of commitment already attained by the transplanted cells. The resulting cell clones showed normal characteristics of cytodifferentiation and cell number. The results indicate that epidermal progenitors perform a maximum of three mitoses during embryonic development, whereas neuroblasts may perform more than ten mitoses. Clone size distribution is in both cases scattered, suggesting either a rather irregular mitotic pattern or cell death. As indicated by heterotopic transplantations, the neurogenic ectoderm for the ventral nervous system exhibits different neurogenic abilities in its different regions, decreasing from medial to lateral; we discuss the hypothesis that some medially located cells of the young gastrulating embryo could be committed towards the neural fate before segregating from the ectoderm. On the other hand, the cells of the dorsal ectodermal regions at the same stage seem to be indifferent with respect to commitment, for they are able to give rise to central neural lineages following their transplantation in the neurogenic region.