Worm Breeder's Gazette 13(5): 50 (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 Mutations That Disrupt CAN Cell Migrations.

Wayne Forrester, Gian Garriga

Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720.

The canal associated neurons (CANs), a pair of bilaterally
symmetric neurons in C. elegans, are born in the head and
migrate to the middle of the animal during embryogenesis.
The CANs are bipolar neurons, extending one anterior and
one posterior axon. As a first step toward understanding
the control of CAN migrations, we have taken a genetic approach
to identify genes required for CAN migration.
Two phenotypes are associated with defects in CAN cells.
Laser ablation of both CANs during the first larval stage
causes a distinctive clear (Clr) phenotype, followed
by death (1). Clr animals appear unusually transparent
and have thin, dark intestines. Mutants in which the CANs
fail to migrate to their proper position develop a withered
tail (Wit) phenotype (2). To identify genes required for
CAN migration or function, we screened for Clr or Wit animals
among F2 progeny from approximately 1000 individual F1
animals of mutagenized parents. We identified 31 mutants
with Wit-like phenotypes and 10 with Clr phenotypes. The
Clr phenotype resembled either the phenotype of clr-l
mutants (2 mutations) or the rod-like larval lethal phenotype
of Ras pathway mutants (8 mutations).
To examine CAN morphology and position directly, an integrated
array containing ceh-73 sequences fused to unc-76 and
the jellyfish green fluorescent protein (GFP) was used(3,
4). This reporter, which produced GFP in the CANs, as well
as several cells in the head and tail, was crossed into mutants
identified in the screen. In most mutants, the CANs appeared
normal. The remaining mutants fell into three classes.
Class 1 (2 mutants-both appear to be alleles of clr-l ) mutants
appear to have CAN pathfinding defects; the posterior
axon does not always follow its normal pathway. Class 2
(2 mutants-gm58 and gm71 ) mutants appear defective in
CAN differentiation; CANs are not detected in these rod-like
animals. gm58 and gm71 may be allelic; they have identical
phenotypes and map between lon-l and unc-32. Class 3 (1
epi-1 mutants and l unc-73 mutant) mutants had CAN cell
migration and axon pathfinding defects; CAN cell bodies
are misplaced anteriorly and the axons do not follow their
normal pathways.
The screen described here was successful in identifying
mutations that affect CAN migrations. However, a large
number of mutations that apparently did not affect CANs
also were identified. In addition, mutations affecting
the CANs that did not cause Wit or Clr phenotypes were missed
in this screen. For these reasons, we are now screening
directly for misplaced CANs using the GFP reporter to visualize
References: 1. J. E. Sulston, J. A. Hodgkin, WBG 5#1, 19;
E. Jorgenson, (pers comm); our unpublished observation.
2. J. Manser, W. B. Wood, Dev Genet 11, 49*4 (1990). 3. Generously
provided by J. Zallen and C. Bargmann. 4. M. Chalfie, Y.
Tu, G. Euskirchen, W. W. Ward, D. C. Prasher, Science 263,
802-805 (1994).