Worm Breeder's Gazette 9(1): 33

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.

An Approach to the Molecular Biology of Genes Involved in the Determination of Vulval Cell Lineages

S. Kim and B. Horvitz

Vulval development involves six precursor cells, P3.p-P8.p, each of 
which has the potential to express any one of three cell lineages, 
designated the 1 , 2  and 3  lineages.  A regulatory cell, the anchor 
cell, controls the expression of these lineages.  Homeotic mutations 
have been identified that cause some of the Pn.p cells to adopt fates 
normally characteristic of other Pn.p cells.  Mutations in genes such 
as lin-2 and lin-10 result in a Vulvaless phenotype caused by the 
expression of 3  lineages by cells that would otherwise undergo 1  or 
2  lineages.  The Multivulva phenotype caused by mutations in genes 
such as lin-15 is the result of the transformation of 3 lineages to 1  
or 2  lineages.  Finally, mutations in lin-31 result in the 
uncontrolled expression of 1 , 2  and 3  lineages such that the same 
Pn.p cell in different animals can express any of the three lineages.  
Genes such as these may be involved in anchor cell signaling or in the 
subsequent determination of Pn.p cell lineage.
We are initiating a molecular analysis of the determination of 
vulval cell lineages by seeking clones containing the genes described 
above.  One way to clone genes that have been identified only 
genetically is to induce mutations with a transposon.  John Collins 
and Phil Anderson (personal communication) have isolated mutant 
strains (e.g.  TR679), derived from Bristol Bergerac hybrids, that 
appear likely to have a high frequency of transposition of the 
transposon Tc1.  From TR679, we have isolated 26 putative transposon-
induced mutations in five genes that affect the determination of 
vulval precursor cell fates: lin-2, lin-12, 
s of the mutations in the genes 
lin-10 and lin-12 has been the most extensive.  lin-12 has been 
previously isolated as a molecular clone (Iva Greenwald, personal 
communication) and our genomic blotting studies indicate that our new 
lin-12 allele differs from the wild-type allele by the insertion of a 
Tc1 transposon.  This result provides direct evidence that TR679-
induced mutations can be caused by Tc1 insertion and thus encourages 
us to attempt to isolate other lin genes as molecular clones by 
transposon-tagging in TR679.
In general, we plan to isolate transposon-tagged genes by 
identifying a Tc1 copy that has inserted within the gene.  In the case 
of our new TR679-induced lin-10 allele, unlinked Tc1 copies were 
removed by repeatedly backcrossing the mutant strain with N2.  Next, 
recombinants between lin-10 and two closely linked markers, dpy-5 and 
unc-29, were isolated.  Genomic blotting analysis of these 
recombinants revealed two Tc1 copies that were inseparable from the 
lin-10 mutation.  These Tc1 copies are located within 0.2 map units to 
the left and 0.07 map units to the right of lin-10.  Presumably, at 
least one of these copies lies within the lin-10 gene.  Similar 
analyses for the TR679-induced lin-2, 
s are in progress.