Primary culture of single ectodermal precursors of Drosophila reveals a dorsoventral prepattern of intrinsic neurogenic and epidermogenic capabilities at the early gastrula stage.

We have analyzed the development in vitro of individual precursor cells from the presumptive truncal segmental ectoderm of the Drosophila embryo to study the intrinsic component in the determination of cell fate. For each cultured cell, the original position within as well as the developmental stage of the donor embryo were known. Cells removed from the ventral neurogenic region develop neural clones. Cells from the dorsal ectoderm and from the dorsalmost part of the ventral neurogenic ectoderm develop epidermal clones. These two classes of clones differ with respect to their division pattern, adhesiveness, cell morphologies and the expression of cell-specific markers. Mixed neural/epidermal clones were obtained from a fraction of precursors at almost all dorsoventral sites. We conclude that, at the onset of gastrulation, precursor cells of the truncal segmental ectoderm already have the capability to develop as either neuroblasts or epidermoblasts in the absence of further cell interactions. At the same time, positional cues distributed along the dorsoventral axis equip precursors with intrinsic preferences towards the neural or epidermal fate, thus defining a prepattern of high neurogenic preferences ventrally, and high epidermogenic preferences dorsally. It is likely that this prepattern is involved in defining the extent of the ventral neurogenic and dorsal epidermogenic regions of the ectoderm. The roles of intrinsic capabilities versus extrinsic influences in the regulation of the characteristic pattern of segregation of the two lineages are discussed.