Worm Breeder's Gazette 8(2): 5

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.

Screens for Maternal Effect Lethal Mutations

J. Priess, K. Kemphues, N. Wolf, D. Hirsch

We are using a new screen in our efforts to collect and characterize 
maternal effect lethal mutations.  The screen allows for rapid 
identification of both conditional and non-conditional maternal effect 
lethals but can also be used to identify fertilization defective and 
gonad defective mutations.  The screen utilizes the fact that fertile 
vulvaless mutants are consumed from within by their progeny, becoming 
non-motile bags of worms.  If however, for any reason, progeny are not 
produced by vulvaless worms, the worms will continue to live.  
Maternal effect lethals, steriles, and gonad defective mutants are 
identified by scoring F2 on plates from cloned F1 of mutagenized lin-2(
e1309); him3(e1147) hermaphrodities.  Plates with F2 survivors after 
three days at 25 C, are candidates.  Maternal effect lethals are 
distinguished from fertilization and gonad defective mutants under the 
dissecting scope because they accumulate fertilized eggs.  Mutations 
are recovered from the heterozygous siblings and maintained by 
selection.  Males produced by the him-3 mutation are used for 
outcrosses.
We have used two screening strategies.  The first screen over the 
entire genome, was performed to test the feasibility of the screen and 
to determine a rough estimate of the genomic distribution of the 
mutations.  The second screen utilizes the balancer chromosome C1 to 
focus on a smaller portion of the genome for saturation analysis.
In our first screen, 23 EMS-induced maternal effect lethal mutations 
were identified from 1600 F1's.  Among these are two temperature-
sensitive, leaky mutants; the remainder are non-conditional and 100% 
penetrant.  15 are not rescued by mating to wild type males (strict 
maternals), 6 are rescued (partial maternals), and two have yet to be 
tested.  The mutations are distributed as follows: LG I-5, LG II-4, LG 
III-4, LG IV-2, LG V-3, LG X-2 (three remain to be tested).  The 
phenotypes of these mutants are for the most part distinguishable one 
from the other, and affect such processes as eggshell formation, 
meiosis, pronuclear migration, P granule segregation, nuclear 
morphology, cell cycle rate, and cytoplasmic behavior.
From the results of this initial screen we conclude that: 1) the 
method is effective in recovering both strict and partial maternal 
effect lethal mutations, 2) loci that mutate to maternal effect 
lethality are numerous, 3) such loci are present on all six linkage 
groups, 4) and a wide variety of phenotypes can be obtained.  The 
screen utilizing the LGII balancer C1 is the same as above except that 
the screening strain is lin-2(e1309); 0)/C1,dpy-10(
e128)unc-52(e444).  This allows us to identify immediately maternal 
effect linked to chromosome II and balanced by C1.  Of 4500 F1's 
screened thus far, 24 chromosome II maternal effect lethal mutations 
have been identified.  They fall into 16 to 18 complementation groups (
two have yet to be tested) and are evenly distributed over the 
balanced portion of LG II.  Six are allelic to previously identified 
maternal effect lethal mutations in three genes (we recovered four new 
alleles at the zyg-9 locus).  Preliminary analysis indicates that 
there is a reasonable mix of strict and partial maternal effects among 
the mutants, and that complementing alleles show distinguishable 
phenotypes.