DEVELOPMENTAL EXPRESSION AND BIOCHEMICAL-ANALYSIS OF CONULIN, A PROTEIN SECRETED FROM A SUBSET OF NEURONAL GROWTH CONES

In this report, we analyze the developmental pattern of expression of a new grasshopper protein, Conulin, using the monoclonal antibody 7D2 on whole-mount embryos and dissociated neurons. We also have examined its biochemical properties by immunoblot analysis. Conulin is a protei n expressed by a subset of neurons in the grasshopper embryo. The mono clonal antibody 7D2 recognizes Conulin as an M(r) 190 x 10(3) protein that is found in both the soluble and membrane-bound fractions of embr yonic proteins. The membrane association is disrupted by alkaline pH a nd high ionic strength. Conulin first is expressed and stored in vesic les inside the cell bodies and axons of central and peripheral neurons . Later, Conulin is detected on the cell surface, but exclusively in t he central nervous system neuropil. This expression is confined to a s ubset of nerve growth cones. Conulin is detected on growth cones only after pioneer neurons have outlined the axonal scaffold. Immunocytoche mistry on cultured embryonic neurons demonstrates that the neurons hav e the autonomous ability to target Conulin to the growth cones. The pr otein is secreted but remains transiently associated with the growth c one plasma membrane. The discovery of Conulin confirms the existence o f proteins specific for the nerve growth cone. Its transitory presence during axonogenesis in only a subset of follower growth cones suggest s that Conulin is involved in guidance through selective fasciculation with pre-existing axons within the ganglionic neuropil.