Membrane glycoproteins immunologically related to the human insulin receptor are associated with presumptive neuronal territories and developing neurones in Drosophila melanogaster.

We have generated a monoclonal antibody (Mab E1C) that recognizes the differentiated nervous system in Drosophila embryos. At the cellular blastoderm stage, Mab E1C behaves as a general ectodermal marker but, in subsequent stages, it also labels the mesoderm. As neurogenesis takes place, staining increases within the neuromeres and is almost exclusively restricted to the nervous tissue by the time neuronal differentiation is completed. In third instar larvae, Mab E1C stains the central nervous system (CNS) as well as the imaginal discs which display a staining pattern related to their degree of neuronal differentiation. No labelling can be detected in adult brains or ovaries. Western blots are consistent with this developmental profile and allow the characterization of a major glycoprotein of 135 X 10(3) Mr (135K) which cosediments with a membrane fraction prepared from embryos. Additional glycoproteins (100K and 80K) are extracted from embryo homogenates by immunoaffinity procedures. In larvae, the 100K polypeptide is not detected. The properties of the 135K and 100K components are highly reminiscent of the molecular pattern of the Drosophila insulin receptor homologue (Petruzzelli et al. (1985) J. biol. Chem. 250, 16072-16075). It is shown that a Mab directed against the human insulin receptor stains the same cells as Mab E1C in imaginal discs and in the CNS. Moreover, this Mab cross-reacts with the 135K and 100K components of the embryonic antigen E1C.