Worm Breeder's Gazette 4(1): 32
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.
A set of eleven temperature-sensitive abnormal embryogenesis mutants
was isolated in the laboratory of S. Ward by J. Miwa and K. Lew.
These were selected for study from a larger collection by the
following criteria: They express an embryonic arrest phenotype (at 25
C adults produce fertilized eggs that do not hatch), their brood sizes
are high (number of viable progeny at 16 C and number of blocked eggs
at 25 C ), and the number of viable progeny at 25 C is very low (about
5 individuals hatch per 1000 eggs laid). Four of these mutants have a
second phenotype: Three are gonadogenesis defective and the fourth
produces non-viable larvae when shifted to 25 C between hatching and
early L4 stage, this phenotype is semidominant. The other phenotypes
are recessive. We have mapped these 11 mutants by complementation
tests and two-and three-factor crosses. They define nine genes (emb-1 -
emb-9). Eight mutants (6 genes, emb-1, emb-5,
emb-8, cluster on LG III
near dpy-17.The stage in embryogenesis at which mutant individuals
stop development at 25 C has been determined. Five classes can be
distinguished. Mutants in emb-1 (2 alleles) do not enter the
proliferation phase and stop in the one-cell stage. One mutant (emb-6)
stops during the proliferation phase in a visibly abnormal 14-cell
stage. Six mutants in 5 genes (emb-2, emb-4,
emb-7) apparently complete proliferation and stop
in the beginning of the morphogenesis phase between the lima bean and
tadpole stages (the morphology of arrested embryos is grossly abnormal)
. One mutant (emb-9) stops late in morphogenesis in the pretzel stage
(without visible abnormalities). One mutant (emb-8) has osmotically
sensitive eggs, which stop at various stages during the early
proliferation phase.
Genetic tests for parental effects similar to the tests described by
Hirsh et al. (Molecular Biology of Eukaryotic Systems, Wilcox,
Abelson, Fox, (eds.) Academic Press, 1977 pp 347-356) show that the
mutants belong to three classes. For 7 genes (9 mutants) maternal
gene expression is necessary and sufficient, for one gene (emb-2, one
of the 'lima bean stoppers'), either maternal or zygotic gene
expression is sufficient and for the mutant in emb-9 ('pretzel
stopper') zygotic gene expression is necessary and sufficient for
normal embryogenesis.