Journal of Neuroscience, Vol 16, 663-674, Copyright © 1996 by Society for Neuroscience
Developmental expression and biochemical analysis of conulin, a protein secreted from a subset of neuronal growth cones
D Sanchez, MD Ganfornina and MJ Bastiani
Biology Department, University of Utah, Salt Lake City 84112, USA.
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 protein
expressed by a subset of neurons in the grasshopper embryo. The monoclonal
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 embryonic
proteins. The membrane association is disrupted by alkaline pH and high
ionic strength. Conulin first is expressed and stored in vesicles inside
the cell bodies and axons of central and peripheral neurons. Later, Conulin
is detected on the cell surface, but exclusively in the central nervous
system neuropil. This expression is confined to a subset of nerve growth
cones. Conulin is detected on growth cones only after pioneer neurons have
outlined the axonal scaffold. Immunocytochemistry on cultured embryonic
neurons demonstrates that the neurons have the autonomous ability to target
Conulin to the growth cones. The protein is secreted but remains
transiently associated with the growth cone plasma membrane. The discovery
of Conulin confirms the existence of proteins specific for the nerve growth
cone. Its transitory presence during axonogenesis in only a subset of
follower growth cones suggests that Conulin is involved in guidance through
selective fasciculation with pre-existing axons within the ganglionic
neuropil.