Worm Breeder's Gazette 13(5): 39 (February 1, 1995)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

A Screen For Lethal Synaptic Function Mutations.

Karen Yook, Erik Jorgensen

Universitv of Utah, Dept. of Biology. UT 84112

Our goal is to identify proteins that function at all synapses.
These include proteins that are involved in svnthesis,
packaging, transport and the release of neurotransmitters
into the synaptic cleft, as well as proteins involved in
the recycling of synaptic vesicles. Initially we screened
for mutants that behaved as if they were defective for both
GABA and acetylcholine function: 11 genes were defined
by this approach. One drawback with such a screen is that
it will fail to identify lethal mutations. We have developed
a screen which can potentially identify lethal mutations
that interfere with neurotransmission.
Aldicarb is a pesticide that inhibits the breakdown of
acetylcholine in the synaptic cleft. The resulting accumulation
of acetylcholine in wild-type worms results in paralysis.
whereas worms lacking or having reduced acetylcholine
transmission are resistant to the drug and continue to
move. It was noted that many of the genes uncovered in the
behavioral screen conferred resistance to aldicarb as
double heterozygotes with n2813. an allele of unc-13 (for
example unc-13/+: snt-l/+). Apparently neurosecretion
is very sensitive to the dosage of proteins required for
this process. This sensitivity allowed us to screen for
haploinsufficient mutations in a background sensitized
by the unc-13 mutation. We mutagenized wild-type males
and crossed them to a strain containing unc-13 (n2813)
(see Figure below). In the Fl we picked aldicarb-resistant
individuals. Lethal mutations in genes that are essential
to synaptic function are maintained as aldicarb resistant
We are interested in two classes of mutations: The first
class are lethal mutations, identified as strains that
are resistant to aldicarb when unc-13 is heterozygous,
and also throw lethal progeny. The second class are homozygous
viable aldicarb-resistant mutations that can be separated
from the unc-13 mutation. Of 2336 genomes scored. we uncovered
62 possible lethal mutations and 61 homozygous viable
aldicarb-resistant mutations. In the homozygous viable
class we found both uncoordinated and wild-type mutants.
All of these strains have satisfied preliminary criteria
for synaptic function mutants and we are confident that
our screen will be successfill in uncovering genes of interest.
One mutation pulled out of the modified screen has been
shown by noncomplementation to be an allele of unc-26,
mutations of which are known to be resistant to Aldicarb
(J. Rand, personal comm.).