Worm Breeder's Gazette 12(2): 104 (January 1, 1992)

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.

Screen for mutations affecting the Muv phenotype of a lin-12 (d)mutation

Diane Levitan, Iva Greenwald

Department of Molecular Biology, Princeton University, Princeton, NJ 08544

We have been conducting a mutagenesis to identify mutations in genes required for generation of the VPC's or with functions in the determination or execution of the 2° VPC fate. We started with a strain of genotype lin-12 ( n950 ); him-5 ( e1467 ),which is Egl- (due to the absence of an anchor cell) and Muv (due to the expression of the 2° fate by all six VPC's). After EMS mutagenesis, we look for reversion of the Muv defect without concomitant reversion of the Egl- defect, in order to screen against mutations that affect lin-12 activity (e.g. Thomas et al., WBG 9(1): 60, 1985). We clone individual F1 progeny of mutagenized parents and examine their F2 and F3 progeny for the presence of Egl- non-Muv animals. In addition to identifying fertile zygotic mutations which might also have been obtained in related screens (e.g. Clark and Horvitz, WBG 10 (2):45, 1988 and WBG 10 (3): 134, 1988; Aroian et al., WBG 10 (3): 132, 1988 ), this screen would allow us to recover maternal-effect mutations, mutations that result in sterility, and mutations that disrupt the regular number or character of the pseudovulvae.

So far, we have screened 7000 F1 animals and have identified eight strains in which the lin-12 ( n950 )Muv phenotype is suppressed. In two strains, the VPC's are absent. Animals of one of these strains are slightly uncoordinated and animals of the other strain are sterile. We don't yet know if the mutations in these strains correspond to known VPC generation genes. Four strains appear to contain mutations that affect lin-12 activity since the Egl- non-Muv phenotype is sensitive to lin-12 dosage.

Strains carrying either of two alleles, ar131 and ar133 ,result in an egg-laying defective phenotype in a lin-12 (+)background. Both alleles are recessive and fail to complement each other for both the Egl- phenotype and suppression of the Muv phenotype of n950 .The gene defined by these two alleles maps to the left arm of LGX, to the left of dpy-3 .Surprisingly, analysis of the VPC lineage in ar131 animals revealed no significant lineage defects. However, the "christmas-tree" structure that occurs during normal morphogenesis of the vulva was aberrant in these animals. Preliminary analysis of the VPC lineage in lin-12 ( n950 ); ar131 animals revealed that 2° VPC lineages still occur; however, pseudovulvae are not formed. One hypothesis consistent with these data is that ar131 results in vulval cells that do not undergo morphogenesis properly. To test this possibility, we are currently constructing double mutants with ar131 and other mutations that result in a Muv phenotype.