Worm Breeder's Gazette 10(3): 100

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.

Studies of the Multivulva Gene lin-34

Greg Beitel and Bob Horvitz

Mutations in the gene lin-34 IV result in a dominant multivulva (Muv)
phenotype that is characterized by the presence of multiple 
protrusions along the ventral side of the animal.  lin-34 is one of 
only two genes in the vulval development pathway for which a dominant 
Muv allele has been identified.  The dominant (and until recently only)
allele of lin-34, n1046, is amber suppressible.  However, the 
dominant effects of n1046 suggested that this allele is not null.  We 
are now attempting to define the null phenotype of lin-34.  In 
addition, we have characterized another putative lin-34 allele, n1700, 
which is also semidominant.
The original allele of lin-34, n1046, was identified by Chip 
Ferguson in a general screen for vulval mutations.  In contrast, n1700 
was found by Dianne Parry as a dominant suppressor of the vulvaless (
Vul) phenotype of lin-10 mutants.  We mapped n1700 and n1046 relative 
to mec-3, aps 0.03 mu to the left 
of dpy-20; n1046 has not been separated from dpy-20 and is within 0.03 
mu of dpy-20.  Deficiency mapping of n1700 showed that sDf2, which 
deletes dpy-20, uncovers n1700, whereas sDf8 and sDf10, both of which 
break to the left of dpy-20, do not uncover n1700.
The n1046 and n1700 mutants have similar penetrances when homozygous 
(-95%), heterozygous with a wild-type chromosome (-20%) and 
heterozygous with a deficiency chromosome (-0%) at 20 C, and they also 
show a similar temperature dependence.  The penetrance of n1046/n1700 
is 95%.  Taken together with the mapping data, these results suggest 
that n1700 is indeed a second allele of lin-34.  Recently, in a screen 
for suppressors of let-341(n1613), Scott Clark isolated a semidominant 
Muv mutation, n1849, that appears to be a third allele of lin-34 (see 
the abstract by Scott Clark and Bob Horvitz in this Newsletter).
The current alleles of lin-34 appear to be gain-of-function 
mutations that increase the level of wild-type lin-34 activity, 
because lin-34(sd)/lin-34(sd) homozygotes are more mutant than the lin-
34(sd)/+ heterozygotes, which in turn are more mutant than lin-34(sd)
/Df heterozygotes.  Furthermore, the wild-type phenotype of the 
heterozygote lin-34(sd)/Df suggests that it should be possible to 
obtain loss-of-function alleles by mutagenizing lin-34(sd) homozygotes 
and cloning phenotypically wild-type F1 progeny.  In a screen of 
approximately 8,000 EMS-mutagenized haploid genomes, 17 strains 
suppressed for the penetrance of the Muv phenotype of n1700 were found.
The ten strongest suppressors were analyzed further.  All ten are 
extragenic, and seven are viable as homozygous suppressed strains in 
which the Muv phenotype is suppressed more than 80%.  Three strains 
could not be homozygosed for the suppressor activity, and may define 
dominant suppressors with a recessive lethal phenotype.  The 
characterization of these extragenic suppressors and efforts to obtain 
intragenic suppressors are continuing.