Worm Breeder's Gazette 10(2): 59

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.

Suppressors of par-2

Niansheng Cheng and Ken Kemphues

We are engaged in reversion study of par-2III, a maternal gene we 
reported earlier (WBG 9:2 p. 72).  The ts mutation it5 is used to 
screen for suppressors.  Homozygous it5 worms at 25 C give rise to 96% 
dead embryos.  Less than 1% of the survivors are fertile.  At 16 C, 
however, they produce 74% living progeny with 24% being fertile.  Thus,
the it5 homozygous strain can be maintained at 16 C but is 
genetically lethal at 25 C.  For suppressor hunting, it5 worms are 
grown synchronously at 16 C on large plates with concentrated bacteria.
The young hermaphrodites are collected and treated with EMS.  Four 
to twelve hours after the treatment, they are hypochlorited to obtain 
a synchronous F1 population.  The F1 embryos are distributed onto 
large plates and the number of L1's is estimated after hatching.  When 
the F1's grow to adults, the worms are pooled and hypochlorited to 
obtain F2 embryos.  The F2's are shifted to 25 C before they reach L4 
stage (prior to oogenesis).  After two generations at 25 C, F4's are 
cloned as putative revertant stocks.
We have recovered seven putative revertants after screening about 67,
000 chromosomes, in eight independent mutageneses.  The frequency of 
1/10,000 is probably an underestimate of actual frequency, because we 
kept only one revertant from each successful mutagenesis.  The 
healthiest revertant among the seven was chosen for further analysis.  
This revertant carries a new mutation, it76, that is a dominant, 
extragenic suppressor to it5.  It maps to chromosome II to the left of 
dpy-10, but we do not yet know its precise map position.  it76 
restores viability and fertility of it5 to nearly wild-type level.  
But unfortunately, it76 alone has no obvious phenotype.  We have 
tested the suppression specificities of it76.  It suppresses five par-
2 mutations thus far tested (e2030, it5, it49, it53 and it58).  
However, it does not suppress par-1(b274), 2), 
7) and par-5(it55).  Therefore, the suppression of 
it76 is gene specific to par-2, but is allele nonspecific.  Thus, it76 
is unlikely to be an informations suppressor and it may identify a 
gene that can be mutated to replace the wild-type function of par-2.