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

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neuron-specific GFP reporters.
In the pan-neural CeKal-1 lines, we observe a
highly penetrant (50%) severe short stop
phenotype in the AIY interneuron, a phenotype
notably distinct from the sprouting phenotype
that results from cell-autonomous expression of
CeKAL-1 in AIY. A double mutant expressing
CeKAL-1 both in AIY and pan-neurally shows
both the short stop and sprouting phenotypes,
indicating that pan-neural expression of
CeKAL-1 does not interfere with its
cell-autonomous effect in this case.
In the pan-neural CeKAL-1 lines we also
observe, in addition to several low penetrance
(less than 10%) axon pathfinding defects, a
striking and moderately penetrant (15-25%)
axon pathfinding defect in the amphid sensory
neurons. Whereas the axons of these neurons
normally enter the nerve ring through the
amphid commissure, in the pan-neural
CeKAL-1 lines, DiI filling reveals altered
pathfinding: These axons, as a fascicle,
sometimes wander in any direction or more
frequently enter the nerve ring directly via a
lateral route. We note that this phenotype is
unlikely to result from a general defect in dorsal
to ventral pathfinding since dorsally to ventrally
directed processes of the touch neurons show
wild type routing. Visualization of this lateral
entry phenotype using a GFP reporter specific
for AFD reveals that the axons of AFDL and R
appear to successfully meet in the nerve ring
even when one or both partner takes a lateral
entry route. We also see that this axon
pathfinding defect is frequently associated with
ectopic neurites originating at the neuronal cell
bodies.
We note that in sax-3(ky200) and unc-6(ev400)
mutants the amphid commisure axons also take
a lateral route into the nerve ring (2), and we are
investigating whether the pan-neural CeKAL-1
lateral entry phenotype may be dependent on
ROBO or netrin.
1. Bülow, H., Berry, K., Zhu, J., and Hobert, O.
Worm Breeders Gazette16(4): 28 (Oct. 1, 2000)
2. Zallen, J., Kirch, S., and Bargmann, C. (1999)
Development, 126:3679-3692.
930. C. elegans rac GENES
CONTROL AXON GUIDANCE, CELL
MIGRATION, AND CELL-CORPSE
ENGULFMENT
Peter Reddien 1 , Erik Lundquist 2 ,
Erika Hartwieg 1 , Cori Bargmann 3 ,
Bob Horvitz 1
930
1 HHMI, Dept. Biology, MIT, Cambridge, MA
02139 USA
2 Dept. Molecular Biosciences, Univ. Kansas,
Lawrence, KS 66045 USA
3 HHMI, UCSF, San Francisco, CA 94143 USA
Rac GTPases control cell polarity via regulation
of the actin cytoskeleton. The pathways and
developmental events controlled by Rac genes
remain largely unresolved. There are three C.
elegans rac genes, ced-10, mig-2, and rac-2.
ced-10 is necessary for the engulfment of cell
corpses generated by programmed cell death,
mig-2 has a role in Q-cell migration, and rac-2
has no previously ascribed function. C. elegans
Rac regulatory proteins have been identified:
CED-10 is regulated by CED-2 CrkII and
CED-5 DOCK180 for phagocytosis, and
UNC-73 Trio is a guanine nucleotide exchange
factor that can act on Rac GTPases. To
determine the developmental roles of and the
pathways that control the three C. elegans rac
genes, we examined axon guidance, cell
migration, and engulfment in animals deficient
for the function of one or more of the rac genes
and/or Rac regulatory genes.
We found that ced-10, mig-2, and rac-2 function
redundantly to control axon guidance, as
determined using ultrastructural studies and cell
type-specific GFP reporters. Perturbing the
function of one rac gene led to no defects in
axon guidance, whereas perturbing the functions
of any two rac genes did. All three rac genes
appear to interact with unc-73 for axon
guidance. ced-10; mig-2 double mutants showed
severe defects in axon guidance, but ced-2;
mig-2 and ced-5; mig-2 double mutants did not.
Thus, ced-10 acts independently from ced-2 and
ced-5 for axon guidance, indicating that Racs
can be regulated by different proteins for the
control of different developmental events.
ced-10, mig-2, and rac-2 act redundantly, and
together with unc-73, to control CAN cell
migration; by contrast, ced-10 and mig-2 but not