Worm Breeder's Gazette 7(1): 87

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.

Two Maternal-Effect Embryonic Lethals that are Suppressed by sup-7(st5)X

B. Wood

Five absolute embryonic lethal mutant alleles showing a strict 
maternal effect (M,M: mutant animals produce no viable embryos after 
mating with N2 males), linked to dpy-10 II or unc-4 II, and carried as 
balanced heterozygotes were roughly mapped relative to the linked 
morphological marker and tested for suppressibility by sup-7(st5) X.  
The five alleles, all recovered following EMS mutagenesis, were ct1 
and ct5 (isolated by John Laufer) and mn40, mn202, and mn203, obtained 
from R.  Herman.  Three of them, ct1 (2% to the right of dpy-10), ct10 
(2% to the left of unc-4), and mn203 (about 2% from unc-4) were not 
suppressed; crosses of the corresponding balanced heterozygotes with 
sup-7 males gave no higher frequency of fertile morphologically marked 
F2 animals than expected from recombination.  However, a balanced 
heterozygote carrying mn40 (1% to the left of unc-4) in similar 
crosses gave about 50% fertile F2 Unc progeny (1 to 50 viable embryos; 
unc-4mn40 homozygotes normally produce many defective embryos with <0.
02% viability).  A balanced heterozygote carrying mn202 (22% to the 
right of unc-4) in crosses with sup-7 males carrying the suppressible 
allele dpy-18(e364) III gave about 40% fertile F2 Unc progeny as 
expected from recombination.  Suppression was demonstrated by picking 
semiDpy unc-4mn202/+;dpy-18/dpy-18;sup-7/+ F2 hermaphrodites and 
showing that their nonDpy Unc progeny produced viable embryos, whereas 
their Dpy did not.  Some semiDpy Unc progeny 
also produced viable embryos; the frequency was uncertain due to the 
difficulty of unequivocally distinguishing semiDpy from nonDpy and Dpy 
animals.  These results show that both mn40 and mn202 are suppressible 
and suggest that both are suppressed marginally by one copy of sup-7 
and better by two copies.
Suppressed lethals (unc-4mn;sup-7), easily distinguishable from 
recombinants by their reduced fertility and slower development, were 
isolated from each of these crosses and shown by backcrossing to carry 
the lethal mn allele.  The suppressed lethals can be maintained near 
20 C but not at lower or higher temperatures; at 16 C sup-7 is lethal, 
and at 25 C it suppresses the mn alleles poorly.
The genes defined by mn40 and mn202 must be transcribed during 
oogenesis.  Neither mutant homozygote produces viable embryos 
following mating with sup-7 males, consistent with the possibility 
that the corresponding messages are also translated prior to 
fertilization.  We are attempting to determine the translation period 
by temperature-shift experiments, taking advantage of the temperature-
sensitive properties of sup-7.  We are also using these mutants in 
attempts to detect transformation of worms with cloned suppressor 
genes introduced by microinjection.