Journal of Neuroscience, Vol 11, 3471-3480, Copyright © 1991 by Society for Neuroscience
A mannose-specific recognition mediates the defasciculation of axons in the leech CNS
B Zipser and RN Cole
Department of Physiology, Michigan State University, East Lansing 48824.
We are studying a mannose-specific recognition mediating the projection of
axons in the synaptic neuropil of the embryonic leech CNS. A functional
class of neurons, the sensory afferents, can be distinguished by a
mannose-containing epitope that is asparagine-linked to a 130 kDa surface
protein and is reactive with the monoclonal antibody Lan3-2. Sensory
afferents project as a tightly fasciculated bundle through peripheral
nerves but, upon arriving in the CNS, defasciculate into the synaptic
neuropil. This defasciculation allows the previously bundled sensory
afferents to form an arborization in the synaptic neuropil. Three lines of
experimental evidence indicate that the defasciculation is mediated by the
sensory afferent's mannose- containing Lan3-2 epitope. The defasciculation
is inhibited (1) by blocking the Lan3-2 epitope with Lan3-2 Fab fragments,
(2) by cleaving the asparagine-linked carbohydrate moieties from surface
proteins with the glycosidase N-glycanase, and (3) by competing for a
putative mannose-binding protein with the neoglycoprotein mannose-BSA
[albumin, p-aminophenyl alpha-D-mannopyranoside (26 mol monosaccharide/mol
albumin)]. In addition to inhibiting the defasciculation, the three
perturbation reagents also elicited the refasciculation of axons that had
defasciculated prior to their application. These three different
experimental approaches provide strong evidence that carbohydrate
recognition regulates the projections of sensory afferents in the leech
synaptic neuropil. Carbohydrate interactions therefore can play a major
role in regulating the neuronal architecture in the CNS.