May mediate or modulate cell adhesion between embryonic cells during development.

(UniProt, P23654)

Three monoclonal antibodies selected because of binding to presumptive imaginal neurons within the larval central nervous system (CNS) (de la Escalera et al., 1990) and an additional one found by virtue of binding to neuronal surfaces in embryos (Hortsch et al., 1990) detected the same ca. 135 kd protein on Western blots of homogenates from embryos, late larva, and pupae. The membrane-bound material is called neurotacin (NRT) because of its expression at points of interneuronal cell contact. Antibody staining (de la Escalera et al., 1990, Hortsch et al., 1990) shows concentration of the protein in dorsal and ventral portions of embryonic blastoderm (where staining appears cell surface-limited), all over gastrulating embryos (although Hortsch et al., 1990, imply a somewhat more restricted expression pattern), in the "proliferating" CNS (including neuroblasts and their progeny) of stage 10-11 embryos, and in regions of contact between neuroblasts. In visceral mesoderm (stage 13), non-neuronal expression diminishes, although it is seen on fat body cells and the "dorsal vessel"; intense staining continues in embryonic CNS (but is relatively weak in axons of motor neurons); PNS expression is evident as well (seemingly restricted to sensory cells that send out multiple dendritic projections, and, in fact, PNS cell-body signals are weaker than on dendrites); cell-surface expression apparent in the various expressing tissues during mid-embryogenesis; in early L1, NRT signals decay but reappear in CNS (in optic formation centers and in neuron clusters and associated axons in ventral cord); the protein's expression persists in imaginal neurons through mid-pupal stage, wanes as such cells complete maturation, and is undetectable in adults. L3 imaginal discs are NRT positive (e.g. on developing chordotonal neurons of leg discs and in developing photoreceptor cells plus their axons, posterior to the morphogenetic furrow). Cell culture studies, including electron-microscope observations (Barthalay et al., 1990), suggest further that NRT is a "contact molecule" between neurons or epithelial cells; there is uniform expression along intercellular contact areas; non-adhesive Schneider-2 cells, transfected with Nrt cDNA, do not become self adhesive, but these cells bind to a subpopulation of embryonic cells.