We have been reverting a hypomorphic
lin-12 allele with the goal of identifying other genes which interact with
lin-12 in the process of cell fate determination. Since this allele has a lowered (but non- null) level of
lin-12 activity, the screen is primarily designed to detect loss of function mutations in negative effectors of
lin-12, in contrast to screens involving reversion of
lin-12(d) alleles (Ferguson et al, CSH Mtg., 1983; Thomas and Horvitz, CSH Mtg., 1987).
lin-12(
n676n930) is an intragenic revertant of the mild
lin-12(d) allele
n676 and appears to be a hypomorph by several criteria: 1) the
n930 mutation is tightly linked to the original
n676 mutation; 2) the
n930 mutation eliminates
lin-12(d) activity in cis but not in trans; 3) while most hermaphrodites have one anchor cell, some have two anchor cells like
lin-12(0) animals, and the penetrance of this phenotype is enhanced in trans to a
lin-12(0) allele; and 4) in dosage studies with a
lin-12(d) allele,
lin-12(
n676n930) acts as though it has a level of
lin-12 activity intermediate between that of wild type and
lin-12(0). This allele is temperature sensitive, such that at 15 C mutant animals are phenotypically wild type (Egl+), while at 25 C they are 100% Egl-. Temperature shift experiments demonstrate that the temperature sensitive period is after the L2 stage, so the primary defect in these animals is probably not in the AC/VU decision, but may be in the vulva cells themselves. After mutagenizing
lin-12(
n676n930) hermaphrodites with EMS and screening for eggs in the F2, we have isolated 17 independent extragenic dominant and recessive suppressors. The recessive suppressors have no obvious dissecting microscope phenotype in a lin- 12(+) background, and define at least 3 different complementation groups:
sup-25(
e1948) and sup
(ar22) map on linkage group V between dpy- 11 and
unc-42, near the eT1 breakpoint, and sup
(ar25) maps on the X chromosome between
lon-2 and
unc-58. Initial characterization of sup- 25
(e1948) has shown that 1)
e1948 has no effect on the
lin-12(0) allele
n941; 2)
e1948 does not appear to be allele, state, or tissue specific in that it increases the gain of function Egl- defect of lin- 12(d)/+, and at 15 C, the permissive temperature for
lin-12(
n676n930), a large percentage of
lin-12(
n676n930);
e1948 hermaphrodites lack anchor cells like
lin-12(d) hermaphrodites. In light of the recently discovered homology between
lin-12 and glp- 1 (John Yochem), we point out that none of these suppressors has a dumpy phenotype.
dpy-10(
e128), which suppresses some ts
glp-1 mutants (Eleanor Maine), and various other dpy markers checked during the course of mapping experiments do not suppress
lin-12(
n676n930).