Worm Breeder's Gazette 1(1): 11

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.

Isolation of Temperature Sensitive Mutants

K. Lew, J. Miwa

Following methods similar to those described by Hirsh and 
Vanderslice (1976), we have isolated more than 100 ethyl methane 
sulfonate induced temperature sensitive (TS) mutants.  All these 
mutants propagate at 20 C (permissive temperature) and do not 
propagate at 25 C (nonpermissive temperature).  These mutants fall 
into four broad classes: 1) mutants blocked in embryogenesis (over 30 
mutants); 2) mutants blocked in fertilization (nearly 30 mutants); 3) 
mutants defective in gonadogenesis (over 30 mutants); 4) mutants 
accumulating in one of the postembryonic larval stages (over a dozen 
mutants).  From this pool of mutants, we have chosen to analyze those 
mutants that are blocked in fertilization and those that are blocked 
in embryogenesis.
Of the 30 or more embryonic mutants that we have examined, mutants 
are found which produce embryos blocked in the 1-2, 12-16, 20-30, 40-
60, and 100-150 cell stages.  Twelve mutants which we have tested so 
far lay embryos that appear to be uniformly blocked in one particular 
cell stage at restrictive temperature.  Their phenotype is recessive 
to wild type.  From temperature shift experiments, we have found that 
the temperature sensitive period in the mutants varied from the first 
larval stage to the adult animal.
We have also asked whether the embryonic defects of these mutants 
show a maternal effect.  Our criteria for maternal effect is the same 
as that described by Vanderslice and Hirsh (1976).  1) When a 
homozygous TS/TS hermaphrodite is mated at nonpermissive temperature 
with wild-type males (+/+), no viable progeny should be produced.  2) 
When a heterozygous hermaphrodite (+/TS) is grown at the nonpermissive 
temperature for the TS mutation, one fourth of the progeny produced 
should be homozygous for the TS mutation.  A dozen embryonic mutants 
blocked in the 1-2, 12-16, 20-30, 40-60, and 100-150 cell stages have 
been characterized.  We have found they all exhibit a maternal effect. 
Two mutants that die after the 150 cell stage may not show a maternal 
effect.  Since the spectrum of the mutants that we tested probably 
represents the general developmental stages of the worm and since all 
mutants so far tested exhibited maternal effect, one can conclude that 
maternal genome plays a major role in the embryonic development of C.  
elegans at least through the 150 cell stage.