Mutations that prevent the formation of competent Pn.p cells or the expression of vulval lineages confer a vulvaless (Vul) phenotype. Previously (WBG 10(2): 45 1988; WBG 10(3): 134 1988), we described the isolation of Vul mutations as suppressors of
lin-15 multivulva mutations. In a screen of 76,000 haploid genomes, we have isolated 156 mutations that suppress
lin-15(
n765ts), of which 80 are Vul. These include mutations in
unc-83,
let-23,
let-341,
lin-10, nSix allelic
lin-15 suppressor mutations (
n1490,
n1760,
n1872ts,
n1880,
n2010, and
n2110 III) cause P(3-8).p to join the hypodermal syncytium without dividing. This Vul phenotype is similar to that caused by
n300, a mutation associated with the translocation nT1(IV,V). In N2, the vulval equivalence group cells P( 3-8).p divide at least once and can express vulval-specific cell lineages, while the non-vulval equivalence group cells, P(1,2,9-11).p, join the syncytium without dividing. Unlike most Vul mutants, in which one Pn.p cell division occurs, these new mutants appear to lack the vulval equivalence group. We refer to these mutations as Supervul mutations to distinguish them from other kinds of Vul mutations that allow Pn.p cells to join the vulval equivalence group but not to express vulval lineages. Chris Li (personal communication) observed that
n1760 animals lack the anti-FMRFamide staining normally displayed by the six P(3-8).a- derived VC neurons of the ventral cord. In addition,
ced-1;
n1760 animals possess extra cell corpses in the ventral cord. Together, these observations suggest that the FMRFamide-staining VC neurons die in
n1760 animals. VC neuron death and vulval abnormalities were observed in
lin-39(
n709) animals by Hilary Ellis.
n709 fails to complement
n1490 for at least the Vul phenotype, indicating that these six
lin-15 suppressors are new alleles of
lin-39.
lin-39 maps between
sma-3 and
unc-36 on LGIII. Three of the new
lin-39 mutants (
n1760,
n1880,
n2010) are 100% Vul and slightly Unc, whereas
n1490 and
n2110 are less than 100% penetrant for the Vul and Unc phenotypes.
n1872ts is 100% Vul and Unc at 25 C and 80% Vul and Unc at 15 C.
n709 is only partially egg-laying defective and not Unc; however
n7091nDf16 and
n7091n1490 animals are Vul. Surviving VC neurons are often seen in
n709 animals, but Chris has not seen any FMRFamide-staining VC cells in
n1760 animals. These data indicate that
n709 is probably a weak allele of
lin-39.That both the Pn.a and Pn.p lineages are abnormal suggests that P(3-8) could be expressing a P(1,2,9,10) type of cell lineage in
lin-39 animals (see figure below). We are currently investigating further the nature of the P(3-8) cell lineages and the cause of the Unc phenotype in
lin-39 animals. [See Figure 1]