Synapses modulate the transmission of signals between neurons and targets. At chemical synapses the pre- and postsynaptic cells are separated by a synaptic cleft. The basal lamina (BL) present in the synaptic cleft is distinct from other BLs and is required for synapse formation. How the BL is patterned and functions in synapse formation remains unclear. We have shown that the C. elegans BL proteins, NID-1 and CLE-1, homologs of nidogen and collagen XVIII, are found adjacent to presynaptic zones. Using a synaptobrevin (SNB)::GFP fusion protein we observed defects in DD and VD neuron presynaptic zones in
nid-1 and
cle-1 mutant animals. In particular the presynaptic zones in
nid-1(
cg119) null animals appear diffused relative to wild type animals. The LAR type receptor has been shown to bind the laminin-nidogen complex, via its extracellular domain, and -liprin (LAR interacting protein) via its intracellular domain. Mutations in
syd-2, the C. elegans -liprin, also result in diffused SNB::GFP puncta similar to, but more severe than
nid-1 mutants. We are testing the hypothesis that the C. elegans LAR homologue, PTP-3, may link NID-1 and SYD-2 in synaptogenesis.Previous work has shown that
ptp-3 functions in neuroblasts during epidermal enclosure. In adults endogenous PTP-3 is observed along nerve cords in a punctate pattern, suggesting it is in a position to affect synaptogenesis. Three
ptp-3 alleles have been isolated and appear to affect the two known isoforms of PTP-3 differently.
op147, a Tc1 insertion in the first phosphatase domain, causes enclosure defects but has no synaptic defects.
tm352 specifically removes the long isoform, including the domain known to bind laminin-nidogen in vertebrates. These animals have synaptic defects, but no epidermal enclosure defects.
mu256, isolated by Lisa Williams in the Kenyon Lab, exhibits both epidermal enclosure and synaptic defects.
mu256 animals fail to stain with PTP-3 specific antisera and may be a molecular null.
tm352 and
mu256 animals have subtle changes in SNB::GFP similar to, those seen in
nid-1 animals. Double mutant analysis indicates that
ptp-3 is epistatic to
nid-1 and that
syd-2 is epistatic to both
ptp-3 and
nid-1. We propose two models. First, SYD-2 may act through PTP-3 to pattern NID-1 which subsequently acts to somehow pattern the synapse. Alternatively, NID-1 organization may be signaled via PTP-3 to SYD-2 within the synapse. We are investigating the localization of each molecule in the mutant backgrounds to differentiate these models.