Worm Breeder's Gazette 13(1): 69 (October 1, 1993)

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.

Protruding-vulva (Pvl) mutants identify new loci involved in vulval development

David Eisenmann, Stuart K. Kim.

Department of Developmental Biology, Stanford University Medical Center, Stanford, CA 94305

A large number of mutations that affect vulval development have been isolated by screening for mutants with a Muv or Vul phenotype or by isolating suppressers of these phenotypes. We believe it is likely there are other gene products acting in vulval induction and morphogenesis that may not mutate to a Muv or Vul phenotype, and would not have been isolated in previous screens. Therefore we are isolating mutations leading to a different mutant phenotype, those causing a protruding vulva (Pvl).

We imagine two main classes of mutations that could cause a protruding vulva, as opposed to no vulva or ectopic pseudovulvae. First, mutations that cause the inability of a particular cell(s) (either a Pn.p cell or one of its 22 descendants) to adopt or execute its normal vulval fate. Second, mutations that affect the ability of cells involved in vulval morphogenesis to make contacts or movements required for that process. We are interested initially in the first class of mutations and have therefore screened for Pvl mutants that show a defect in the number or placement of the 22 vulval nuclei when scored in the L4 stage at the start of vulval morphogenesis.

We have screened 38,000 haploid genomes and isolated 230 independent Pvl mutants. Of these, 55 have a defect in the number or placement of their vulval cells when examined by Nomarski microscopy. The remaining 175 mutants resemble wild type at this stage and are candidates for mutations affecting vulval morphogenesis or other processes. At least 20 of the 55 Pvl mutants with vulval cell defects represent new alleles of known genes. So far we have identified alleles of: lin-l, lin-2 , lin-14 , lin-17 , lin-18 , lin-25 , lin-28 , lin-31 , unc-83 , unc-84 and dig-1 .Based on map location and complementation tests we have also identified a number of new loci involved in vulval development. A description of some of these Pvl mutations follows:

Mutations causing defects in Pn.p cell generation: ga96 IIC and ga87 IIC - these mutations both cause fewer than 12 Pn.p nuclei to be present in the L2 .(Average number of Pn.p nuxlei is 5.8 for ga87 and 8.6 for ga96 ).In ga87 animals there are too many ventral cord neurons as well. ga96 animals often have misshapen heads and tails as L1 /L2. ga79 IVL - this mutation causes one or more Pn.p cells to divide early in the Ll or L2 stage, a phenotype also caused by lin-25 and lin-31 .It is unclear yet if this causes the Pvl phenotype of these animals.

Mutations causing defects in vulval induction: ga80 X and ga82 IC - these two mutations both cause one or more of P5 .p-P6.por P7 .pto remain uninduced leading to an Egl, Pvl phenotype. ga80 is located left of unc-10 on X, and ga82 is between unc- l1 and unc-57 on I. ga89 IVC - this mutation causes a temperature-sensitive Muv and partial sterility phenotype. The Muv phenotype is caused by P3 .pand/or P4 .pexpressing an induced (vulval) fate. The fate of P8 .pis only rarely altered by this mutation. These extra inductions still occur in animals in which the precursors to the somatic gonad have been ablated with a laser, therefore ga89 is an anchor cell-independent Muv mutation. This Muv phenotype is epistatic to the Vul phenotype of lin-2 in ga89 ; lin-2 double mutants at 25°.

Mutations causing defects in vulval cell lineages or other processes: ga91 IIC - this mutation causes the 2° cells (P5.p and P7 .p)to undergo the lineage L L L N instead of L L T N. Males do not mate. This mutation is located between dpy-10 and rol-6 . ga97 IVL - this mutation causes one or more of P5 .p- P7 .pto express an incompletely induced lineage (dividing only O - 2 times), resulting in too few vulval cells. Males do not mate. ga97 is located between dpy-9 and lin-l. ga88 VC - this mutation causes the P6 .pxxcells to divide in a non-transverse plane leading to a defect in vulval cell placement in the late L3 . ga81 VL - this mutation causes an early defect in vulval invagination, perhaps due to a defect in the anchor cell (AC). In many ga81 animals the AC is not positioned directly over P6 .pin the L3 at the start of Pn.p divisions. In such animals the normal invagination of P6 .papand P6 .ppadoes not occur and the third division leads to four P6 .pxxxcells in a plane on each side.

All of these Pvl mutations are recessive. In addition we have only one allele for each and do not yet know the null phenotype for any of these loci. Further mapping and genetic epistasis tests of several of these mutations are underway.