Worm Breeder's Gazette 10(3): 135

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.

Suppressors of clr-1(e1745ts) Identify a New Gene Involved in Sex Myoblast Migrations

Michael J. Stern and Bob Horvitz

When raised at the permissive temperature, animals bearing egl-15(
n1477ts) and other viable alleles of egl-15 have abnormal sex myoblast 
(SM) migrations due to a repulsion of the SMs by cells of the somatic 
gonad.  In the last WBG (10(2):46-47, 1988), we described the 
isolation of clr-1 alleles as suppressors of the temperature-sensitive 
inviable phenotype of egl-15(n1477ts).  Many clr-1 alleles isolated in 
this manner cause lethality in the absence of egl-15(n1477ts), making 
these clr-1 and egl-15 alleles mutual suppressors.
To understand better the function of clr-1 and its interaction with 
egl-15, we have isolated suppressors of the temperature-sensitive 
lethal phenotype of clr-1(e1745ts).  Animals bearing this mutation are 
wild-type at 15 C, but at 25 C they are extremely sick, becoming Dpy, 
motionless, and sterile on account of their extreme Clr phenotype.  
Thus, it is very easy to detect mutations that suppress these 
phenotypes.  We have screened animals representing 36,000 EMS-
mutagenized haploid genomes and 90,000 gamma-irradiated haploid 
genomes.  From these screens we have isolated 21 EMS-induced and 3 
gamma-ray induced recessive suppressors.  These suppressor mutations 
define five genes: one on each of LGIII (1 allele), LGIV (4 alleles), 
and LGV (10 alleles including all 3 gamma-ray induced alleles); and 
two genes on LGX, including egl-15 (8 alleles) and a new gene (2 
alleles).  To date, little is known about the autosomal mutations.  
The mutations on LGV cause a recessive scrawny phenotype when isolated 
from clr-1(e1745ts), reminiscent of the phenotype of egl-15(n1477ts) 
at 20 C.  However, animals bearing these mutations are non-Egl and 
have properly positioned SMs.  For all genes except the one on LGV, 
the paucity of EMS alleles and dearth of gamma-ray-induced alleles 
suggest that these alleles are not null.
Eight suppressors on LGX have been assigned to egl-15 on the basis 
of their failure to complement not only egl-15(n1477ts), but also 
putative null allele egl-15(n1454) and the deficiency nDf19, for 
suppression of clr-1(e1745ts).  Unlike the putative null alleles egl-
15 which cause an L1 larval arrest, these suppressors can be 
transmitted by hemizygous males, and the four alleles tested are 
homozygous viable isolated away from clr-1(e1745ts).  Therefore, we 
believe that these are not null alleles of egl-15.  This observation 
is consistent with the finding that clr-1(e1745ts) does not suppress 
the lethality of the putative null allele egl-15(n1454).  Surprisingly,
however, only two of these eight new alleles fail to complement egl-
15(n484) for its Egl phenotype.  Two of the strongest suppressor 
alleles also do not cause an Egl phenotype when separated from clr-1(
e1745ts).  The previously identified viable egl-15 alleles have been 
ordered in an allelic series on the basis of their causing 
increasingly posterior displacement of the SMs: n1459, n484, n1458, 
and n1477ts at 20 C.   The weakest allele in this series, n1459, is a 
weak suppressor, and the strongest allele in this series, n1477ts, is 
a strong suppressor of clr-1(e1745ts).  However, the two intermediate 
alleles in this allelic series do not suppress at all.  Since there 
are egl-15 alleles that cause a strong Egl phenotype but are not 
suppressors of clr-1(e1745ts), as well as alleles that are strong 
suppressors but do not cause an Egl phenotype, egl-15 appears to be a 
complex locus with two mutationally separable domains.
Two mutations (n1779, n1781) define a new gene, sem-5 X (SEx Muscle 
abnormal), that maps to the region between unc-18 and dpy-6, which is 
distinct from the position of egl-15.  We have separated n1779 from 
clr-1(e1745ts) and found that it causes a low penetrance (10%) Egl 
phenotype due to the posterior displacement of the SMs.  Although 
mutations in egl-17 X also cause the posterior displacement of the SMs,
none suppresses clr-1(e1745ts), and no egl-17 alleles have yet been 
isolated in this screen.  It will be interesting to determine how 
these three genes on LGX, and possibly the other clr-1 suppressors, 
function to affect the SM-gonad interaction that controls part of the 
SM migration.