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.

Genetic Characterization, Parental Effects and Terminal Phenotypes of Temperature-sensitive Mutations causing Arrest of Embryonic etc...

J. Miwa, E. Schierenberg, G. von Ehrenstein

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.