Worm Breeder's Gazette 11(3): 68

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 the lin-10 Vulvaless Phenotype

Stuart Kim, Dianne Parry, Kyuson Yun, Jonathan Heuer and Bob Horvitz

We would like to understand how Pn.p cell fates are determined.  At 
least 18 genes have already been identified that specify Pn.p cell 
fates, and we would like to expand this genetic pathway by identifying 
new genes.  In particular, we wanted to identify genes that interact 
with lin-10, and so we isolated mutations that suppress the lin-10 
vulvaless phenotype.  The screen for lin-10 suppressors is powerful 
because lin-10 animals do not have a vulva and thus do not lay eggs, 
whereas one suppressed animal lays many eggs.  Thus, mutants are 
easily isolated by picking eggs laid by the F2 generation of 
mutagenized lin-10 animals.  We have identified over 60 suppressors of 
the lin-10(n1390) vulvaless phenotype after screening the equivalent 
of 150,000 EMS-mutagenized haploid genomes.  One mutation is a gain-of-
function allele of lin-34 that has a semi-dominant multivulva 
phenotype (G.  Beitel, personal communication).  Twenty-seven of the 
remaining suppressors have been analyzed, and they define five new 
genes (termed suv for suppressor of the lin-10 vulvaless phenotype): 
suv-1(12 alleles), suv-2(7 alleles), suv-3(4 alleles), suv-4(2 alleles)
and suv-5(2 alleles).  suv-1 and suv-2 map on LGX; suv-1 maps very 
close to dpy-3, while suv-2 maps between sdc-2 and sma-5.suv-1, which 
has been studied in the most detail, is interesting because it 
interacts with many other vulval determination genes.  suv-1(n1329) 
suppresses the vulvaless phenotype of lin-2(e1309), lin-3(n378), lin-7(
e1413), lin-10(e1439, n1299, n1390) and let-23(n1045), while it 
enhances the multivulva phenotype of lin-15(n309, n765, n767).  Thus, 
suv-1(n1329) increases the expression of vulval cell lineages (1  and 
2 ) in both vulvaless and multivulva mutants.  The fact that suv-1 
interacts with all of the determination genes tested indicates that 
suv-1 is also involved in determining Pn.p cell fates.  However, the 
suv-1(n1329) mutation results in a wild-type phenotype by itself, 
indicating that mutations such as this cannot be isolated directly and 
must rather be isolated in a second level genetic screen, e.g.  as lin-
10 suppressors.
Using an RNAse protection assay, we found that lin-10 transcripts 
were five times more abundant in mixed stage RNA from suv-1 animals 
than from wild-type animals (using act-1 as a control), indicating 
that suv-1 is involved in regulating lin-10 expression, either 
directly or indirectly.  Increased levels of lin-10 expression can 
partly explain how suv-1 acts as a suppressor, since overexpression of 
a partial loss-of-function lin-10 allele could restore gene activity.  
However, suv-1(n1329) suppresses all three of the lin-10 alleles that 
were tested (all of which are candidates for null alleles), suggesting 
that suv-1(n1329) must affect something else in addition to increasing 
lin-10 expression.  One possibility is that suv-1 also regulates the 
expression of other determination genes, such as lin-2, lin-3, lin-7, 
let-23 or lin-15; the misregulation of these other determination genes 
in suv-1 mutants may be able to bypass the functional requirement for 
lin-10 gene activity.  This possibility can be tested once molecular 
probes for these other genes have been isolated.