A synaptic vesicle antigen is restricted to the junctional region of the presynaptic plasma membrane.

Abstract

The plasma membrane of electric organ nerve terminals has two domains that can be distinguished by monoclonal antibodies. A library of 111 mouse monoclonal antibodies raised to nerve terminals from Torpedo californica contains 4 antibodies that bind specifically to the outside of intact synaptosomes. The distribution of the binding sites of these monoclonal antibodies on the outside of intact nerve terminals was examined by immunofluorescence and immunoelectron microscopy. The binding sites of 3 (tor23, 25, and 132) are distributed uniformly over nerve trunks and fine terminal branches. The binding site of the fourth (tor7O) is restricted to synaptic junctional regions. This antibody, but not the other 3, recognizes a major component of synaptic vesicles, a proteoglycan associated with the inner surface of the vesicle membrane. The difference in the pattern of binding of these monoclonal antibodies suggests that the region of the plasma membrane containing active zones is antigenically distinguishable from other nerve terminal plasma membrane. We suggest that the antigen recognized by tor7O is externalized by exocytosis of synaptic vesicles while other plasma antigens take a different route to the surface. The unexpected observation that the vesicle antigen remains on the surface after exocytosis and is prevented from diffusion from the synaptic junctional region would be consistent with an interaction between the vesicle proteoglycan and elements of the synaptic cleft.

The Synaptic Vesicle Protein SV2 Is Complexed with an α5-Containing Laminin on the Nerve Terminal Surface

“…43). These workers hypothesized that this proteoglycan is complexed on the surface of the nerve terminal with synaptic cleft components (15). Here, we tested this hypothesis by characterizing detergent-solubilized SV2 immunoprecipitated from the surface of synaptosomes.…”

“…These are the likely locations for the attachment of the keratan sulfate side chains recognized by anti-SV1 mAb (2). Previously it was shown that the SV1 epitope of SV2 was not only present in synaptic vesicles (4) but on the nerve terminal surface of electric organ synapses as well (15). Based on this finding, Buckley et al (15) hypothesized that this synaptic vesicle proteoglycan was retained on the surface of synaptosomes due to interactions with components of the synaptic cleft.…”

“…Previously it was shown that the SV1 epitope of SV2 was not only present in synaptic vesicles (4) but on the nerve terminal surface of electric organ synapses as well (15). Based on this finding, Buckley et al (15) hypothesized that this synaptic vesicle proteoglycan was retained on the surface of synaptosomes due to interactions with components of the synaptic cleft. In fact, it is known that interactions between the nerve terminal membrane and the extracellular matrix (ECM) of the synaptic cleft are critical for nerve regeneration at the neuromuscular junction.…”

“…We never found the horseradish peroxidase from the first probe to be visualized on x-ray film in the second luminol reaction. (15) demonstrated that SV2H is present on the surface of electric organ nerve terminals both by immunoelectron microscopy and the immunoprecipitation of synaptosomes (reviewed in Ref. 43).…”

Compartmentalization of acetylcholinesterase in the chick retina

“…Barat et al, 1986). Although the CNS does not contain basal laminae as such, the extracellular matrix-like material making up the synaptic cleft does contain GAGS and may provide anchorage points for the collagen-like tails of asymmetric AChE (Buckley et al, 1983). Actually, we have been able to solubilize A-forms, from chick retina, by means of heparin, with an extraction efficiency similar to that observed in "peripheral" tissues (Barat et al, 1986).…”