Program of the 2001 International Worm Meeting - Sternberg Lab ...

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412. syd-5 may play a role in
regulating synapse size in C. elegans
Renee Baran, Yishi Jin
HHMI and Dept. of MCD Biology, Sinsheimer
Labs, University of California, Santa Cruz, CA
95064.
syd-5 (ju89) was identified in a screen for
mutations that alter synapse morphology in C.
elegans using a presynaptic vesicle marker,
Punc-25::SNB-1-GFP (1,2). This marker is
expressed specifically by the GABAergic DD
and VD motor neurons which form inhibitory
synapses onto the body wall muscles. The
sinusoidal movement of C. elegans is generated
by the coordinated action of excitatory
cholinergic motor neurons and the inhibitory
GABAergic motor neurons. In wild-type adult
worms, Punc-25-SNB-1-GFP is expressed as
puncta of uniform size and spacing along the
dorsal and ventral nerve cords. syd-5(ju89)
mutant worms move with reduced sinusoidal
amplitude and exhibit abnormal SNB-1-GFP
puncta of various sizes in an irregular pattern
along the nerve cords. Consistent with a change
in synapse morphology, we also observe similar
defects in the size, shape and spacing of the
post-synaptic GABA receptor marker
UNC-49B-GFP (3) in syd-5 animals.
The SNB-1-GFP phenotype of syd-5 mutants
resembles mutants of rpm-1. rpm-1 encodes a
protein with GEF and ring finger domains.
Ultrastructural analysis of GABAergic synapses
in rpm-1 mutants revealed multiple active zones
within a single presynaptic site (4). To
determine if syd-5ju89) and rpm-1 mutants
exhibit similar defects in synapse morphology,
we examined worms co-stained with antibodies
to GFP and to the active zone marker, SYD-2.
SYD-2 localizes to synapses independent of
neurotransmitter vesicles and is required to
restrict the size of active zones1 . We found a
pattern of enlarged SYD-2 puncta at synapses
with increased SNB-1-GFP and smaller SYD-2
puncta at sites of reduced SNB-1-GFP in the
syd-5 mutants. This phenotype appears to be
distinct from the rpm-1 phenotype, suggesting
that syd-5 plays a role in regulating synapse
size.
syd-5( ju89) behaves genetically as a weak
gain-of-function mutation. Twenty-four
suppressors of syd-5(ju89) were identified
previously from a screen of 30,000 F1 worms.
Four suppressors are linked to ju89 and may
represent loss-of-function syd-5 alleles.
Mapping and characterization of the suppressors
will be presented, along with progress in the
cloning and molecular characterization of syd-5.
1Zhen & Jin. 1999. Nature
2 Nonet, M. 1999. Neurosci. Methods
3Bamber et al., 1999. J. Neurosci.
4Zhen et al. 2000. Neuron
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