EARLY TAGMA-SPECIFIC COMMITMENT OF DROSOPHILA CNS PROGENITOR NB1-1

The developing central nervous system of many species expresses distin ct segment-specific characteristics. We recently described the entire embryonic lineage of Drosophila neuroblast NB1-1 and showed that the c omposition of this lineage differs between the thoracic and abdominal tagmata with respect to the presence or absence of specific glial and neuronal components (Udolph, G., Prokop, A., Bossing, T. and Technau, G. M. (1993) Development 118, 765-775). Here, we demonstrate by hetero topic transplantations that tagma specificity of NB1-1 is determined i n the neuroectoderm at the early gastrula stage (stage 7). Heterogenet ic transplantation and mutant analysis show that the activity of the h omeotic genes Ubx or abd-A is required for the expression of the abdom inal variant of the lineage. Heat induction of Ubx or abd-A expression or their derepression in Polycomb mutant embryos can override thoraci c determination several hours after gastrulation (stage 10/11). At tha t stage antibody stainings reveal both proteins to be present in NB1-1 during normal development. Possible mechanisms conferring the early t agma-specific determination are discussed.