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

431
phenotypes of both mutants are similar, but
ast-2 mutants are somewhat lethargic and
slightly Egl, whereas ast-1 mutants only show
subtle changes in exploratory behaviour.
Two alleles of ast-1 called rh300 and hd1 were
isolated independently. The phenotypes are very
similar and the mutants do not complement. One
allele of ast-2 was isolated so far. ast-2 maps
close to unc-13 on chromosome I. ast-1 maps to
chromosome II four map units left of dpy-10
and near vab-1. ast-1(hd1) complements
vab-1(dx31). Fine mapping was based on single
nucleotide polymorphisms that can be detected
by RFLP as a consequence of the modification
of a restriction enzyme recognition site. The
gene locus has been narrowed to a 400 kb
region enclosed by cosmids ZK430 and
C33F10.
432. RNAi MEDIATED DISRUPTION
OF VEM-1, A NOVEL
MEMBRANE-ASSOCIATED
PROTEIN, PERTURBS THE
PATTERNING OF A SUBSET OF
AXONS IN THE VENTRAL NERVE
CORD
Erik Runko, Zaven Kaprielian
432
Departments of Neuroscience and Pathology,
Albert Einstein College of Medicine, Bronx, NY
A critical phase in the development of the
nervous system is the formation of connections
between axons and their synaptic targets. These
axon pathfinding events are controlled by both
long- and short-range guidance cues that are
expressed by intermediate targets which exist at
various points along a given axonal trajectory.
We have previously identified VEMA as a novel
marker of two vertebrate midline structures that
are important intermediate targets for
midline-crossing axons: the floor plate of the
ventral spinal cord and the optic chiasm of the
ventral diencephalon. Interestingly, VEMA is
also expressed in specific early-developing
neuronal populations as they initiate
axongenesis.
The deduced amino acid sequence of VEMA
contains a single transmembrane domain and
several distinct sorting motifs that are thought to
mediate trafficking of proteins between
intracellular compartments and the plasma
membrane. The C. elegans genome encodes for
a single ortholog of VEMA that is 36 % identical
to the amino acid sequence of vertebrate VEMA.
We refer to the C. elegans ortholog of VEMA as
vem-1. To elucidate the distribution of vem-1 in
embryonic and larval stage C. elegans we
utilized a vem-1::GFP transcriptional reporter
line. Prior to the comma stage, vem-1::GFP was
expressed in distinct neurons of the head ganglia
during the period of axonal outgrowth. During
later stages of embryogenesis (1.5 fold to 3 fold
stage), vem-1::GFP was expressed in pioneer
axons of the developing ventral nerve cord.
Throughout the larval stages and into adulthood,
expression of the vem-1::GFP transgene was
maintained on a specific subset of neurons
located within a variety of head and tail ganglia.
Interestingly, expression in the AVG and
several of the PV neurons suggests a possible
role for vem-1 in regulating the outgrowth