Worm Breeder's Gazette 11(1): 51

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lin-15 is not Cell Autonomous

R.K. Herman

Ferguson and Horvitz (1985 Genetics 110: 17) have described five 
alleles of lin-15, all of which result in vulva-like protrusions on 
the ventral side of the mutant animals--referred to as the multivulva (
Muv) phenotype.  The mutations are recessive to lin-15(+) and appear 
to result in reduced gene activity.  Ferguson, Sternberg and Horvitz (
1987 Nature 326: 259) showed that the vulval precursor cells (VPCs) P3.
p-P8.p in lin-15 animals all express 1  and 2  fates.  The latter 
authors also showed that laser ablation of the anchor cell in lin-15 
animals did not abolish the Muv phenotype; they concluded from this 
result that the site of action of lin-15 was likely to be within the 
hypodermal VPCs and not in the anchor cell.  (Muv mutations in other 
genes also appeared to be independent of the anchor cell signal.)  One 
would thus expect that a mosaic animal in which lin-15(+) was present 
in the VPCs would be non-Muv, regardless of what other cells (
including the anchor cell) might be lin-15.  My results contradict 
this simple prediction.
Among about 7,000 zygotes of genotype unc-93(e1500) III; unc-3 
09) sup-10(0) X; mnDp14(X;f)
[unc-3(+) sup-10(+)], 15 
animals were found that I concluded had suffered duplication loss at 
P1.  These animals were non-Unc-93 non-Unc-3 and gave only Unc-3 
geny.  Seven of the 15 were checked for FITC 
staining and found to be non-Osm-1, as expected.  The VPCs are 
descended from AB and thus should have contained lin-15(+).  Ten of 
the 15 animals had 1-3 ventral protrusions at positions either 
anterior or posterior to the vulva.  Many of the mosaics were thus 
unexpectedly Muv, although the number of protrusions per animal was 
generally less than that found for pure lin-15(n309) animals.  Another 
class of non-Unc-93 non-Unc-3 animal among the same zygotes provided a 
kind of control.  These gave some wild-type (as well as Unc-3 
geny, indicating that their free duplications 
no longer carried sup-10(+).  There were 15 of these animals, and none 
showed any ventral protrusions.  It thus seems unlikely that many of 
the protrusions found in the mosaic animals could be attributed to 
weak dominance of the lin-15(+) gene on the free duplication or to 
frequent extra duplication loss in the lineages leading to the VPCs.
I am in the process of constructing animals that should allow me to 
identify mosaics in which duplication loss occurred at AB or AB.p, 
ancestors of the VPCs.  I would expect that such mosaics might also be 
Muv, i.e., that lin-15(+) is needed both for normal signal generation 
and for normal response to signal.  (I should point out that Ferguson 
et al.  stated explicitly that their results did not exclude this 
possibility.) I would also like to do additional work with the 
duplication-loss-at-P1 mosaics.  First, I hope, in collaboration with 
Ed Hedgecock, to follow the lineages of VPC descendants in such 
animals.  And second, I would like to see if ablation of the anchor 
cell in these animals would abolish their Muv-ness (since the result 
so far only points to an effect of one or more descendants of P1).
I'd like to thank Paul Sternberg for encouraging me to generate 
these mosaics.