Worm Breeder's Gazette 10(2): 46

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.

clr-1 Suppresses the Sex Myoblast Migration Defects of egl-15 and egl-17 Mutants

Michael J. Stern and Bob Horvitz

Mutations in two genes, egl-15 X and egl-17 X, cause defective sex 
myoblast (SM) migrations in the hermaphrodite as a result of the 
repulsion of the SMs by somatic cells in the gonad (C.  elegans CSH 
Meeting Abstracts, 1987, p.  187).  Laser ablation of the somatic 
gonad can rescue the SM migration defects of egl-15 and egl-17 animals,
suggesting that the genetic elimination of the repellant could also 
rescue their phenotypes.  However, the original alleles of these genes 
cause a leaky Egl phenotype, which make reversion experiments 
difficult.  In the last WBG (10(1):115, 1987) we described the 
isolation of new egl-15 alleles, some of which cause an L1 larval 
arrest that we think represents the null phenotype .  One new allele, 
n1477, causes a scrawny, Egl phenotype at 20 C and lethality at 25 C.  
The possibility of easily isolating revertants of the temperature-
sensitive lethal phenotype of egl-15(n1477) led us to see if 
revertants of the lethal phenotype would simultaneously be reverted 
for the SM migration defect, and, thus, provide a method to identify 
the repellant genetically.
EMS-mutagenized egl-15(n1477) animals were grown at 20 C until the 
F1's were gravid and then shifted to 25 C.  The F2 progeny, 
representing approximately 75,000 mutagenized haploid genomes, were 
screened for healthy animals, and 28 revertant strains were recovered. 
These revertants fall into three classes.  (1) Four suppressors are X-
linked based upon male transmission.  One of these alleles has been 
shown to be closely linked to egl-15 and is a semi-dominant suppressor 
of n1477.  We suspect that this allele is an intragenic revertant, and 
are testing to see if the other alleles in this class behave similarly.
(2) The 15 suppressors of the second class are recessive and are 
closely linked to dpy-10 II.  Several of these have been separated 
from n1477 and cause a phenotype in which the worms appear to fill 
with fluid.  The weakest of these phenotypes is a detachment of the 
intestine from the body wall.  The stronger phenotypes are similar, 
but more severe, and the animals die as L2's or L3's.  This phenotype 
and map position are similar to those of clr-1(e1745ts), originally 
described by Ed Hedgecock and Andy Fire (C.  elegans CSH Meeting 
Abstracts, 1985, p.  71) .   clr-1 (e1745ts) animals display the weak 
phenotype at 20 C and are dead at 25 C.  Suppressors in the second 
class all fail to complement clr-1(e1745) for its Clr phenotype at 25 
C.  In addition, clr-1(e1745) suppresses, and is suppressed by, egl-15(
n1477) .  Thus, n1477 suppressors in this class are alleles of clr-1.  (
3) The remaining nine suppressors are recessive, appear to be linked 
to dpy-10, and fail to complement for suppression of n1477 by clr-1(
n1635) .  Thus, they too seem to be clr-1 alleles.  However, they are 
not Clr either isolated away from n1477 nor in trans to clr-1(e1745) 
and need to be mapped more rigorously.  These mutations may define a 
weaker class of clr-1 alleles.
Suppressors in all three classes (nine suppressors examined to date, 
as well as clr-1(e1745)), partially suppress the migration defect of 
egl-15(n1477) .  In addition, clr-1(e1745) is a good suppressor of the 
SM migration defect of egl-17(e1313), although the Clr phenotype is 
not suppressed in the double mutant.  The position of the SM's in clr-
1(e1745); 313) animals at 20 C is similar to that 
in egl-17(e1313) animals with the somatic gonad ablated.  Thus, clr-1(
e1745) can suppress mutations in both genes that affect the 
interaction between the SM's and the somatic gonad, although to 
different extents.  The SM migration is not abnormal in clr-1(e1745) 
animals at 20 C.
Since mutations in egl-15 and clr-1 can cause lethality, these genes 
must be involved in functions besides those controlling the SM 
migration.  Our working model is that egl-15 and clr-1 encode products 
that control opposing processes, so that the absolute levels of their 
gene products are not important as long as their relative levels are 
maintained.  These processes may affect both a function controlling 
the SM migration and at least one other function.  This model predicts 
that null mutations in either gene could not be suppressed.  We are 
currently testing this hypothesis with putative null alleles of egl-15.
The weak Clr phenotype can be phenocopied by orthovanadate (Ed 
Hedgecock, personal communication), a potent inhibitor of ATPases and 
phosphatases in general.  Perhaps clr-1 encodes a phosphatase that 
opposes a kinase encoded by egl-15 and possibly egl-17.Since we have 
found that egl-15(n1477) can suppress clr-1 alleles, we are now 
planning to look for suppressors of clr-1(e1745) with the hope of 
answering the following questions.  First, what type of egl-15 alleles 
can suppress clr-1(e1745)?  Second, can egl-17 mutations suppress the 
Clr phenotype of clr-1(e1745), and, if so, what type of mutations are 
they?  Third, what other genes can be mutated to suppress clr-1(e1745),
and do they affect the SM migration?  In addition, we also plan to 
use the mutual suppression of egl-15 and clr-1 as a means of isolating 
transposon-tagged and gamma-ray-induced alleles of these genes as the 
first step towards cloning them.