Worm Breeder's Gazette 9(3): 80

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 Loci That May Interact During Early Embryogenesis

P. Mains, I. Sulston and W.B. Wood

Figure 1

We have isolated a set of eight dominant, temperature-sensitive, 
maternal-effect lethal mutations which define at least five 
independent loci. As reported in the last WORM BREEDER'S GAZETTE, 
ct46/ct46(I) and ct46/+(I) animals produce embryos with early cleavage 
defects reminiscent of those resulting from defects in the zyg-9(II) 
gene (1), a maternal effect locus defined by six recessive mutations (
2). Mutations at both loci result in a failure of pronuclear fusion, a 
longitudinal first cleavage, and subsequent multiple nuclei per cell. 
If these two loci are interacting to control the same process, a 
synergistic effect might be found when the two mutations are present 
in the same individual. We have constructed animals carrying both ct46 
and the temperature sensitive allele zyg-9(b244) and/or the putative 
null allele zyg-9(b301), which is an amber mutation. At 20 , the 
embryos produced by ct46/+ animals show an intermediate level of 
viability (33% hatch, see Table 1). At this temperature the embryos 
produced by b244 animals are essentially fully viable (though probably 
near some threshold, since viability drops to zero at 25 ). However, 
the embryos produced by ct46/+;b244/b244 animals at 20  show an 800-
fold lower level of viability than predicted if the effects of the two 
mutations were independent. Little or no interaction was seen in 
ct46/+;b244/+. Lowering the level of the zyg-9 gene product by half 
with the null allele (ct46/+;b301/+) also has little or no effect.   
The combination of b244 and b301 (ct46/+;b244/b301) does show the 
synergistic effect. Results obtained with a few other mutant 
combinations are shown in the table. These results show that ct46 acts 
as a dominant enhancer of zyg- 9(b244) (or zyg-9(b244) acts as a 
recessive enhancer of ct46).   This effect, together with the 
similarity of phenotypes resulting from the ct46 and zyg-9 mutations, 
is circumstantial evidence for a specific interaction between these 
loci. As a more direct test of such an interaction, we will try to 
isolate extragenic suppressors of ct46 and see if any are found in zyg-
9, and vice versa. We are also testing other alleles of zyg-9 for 
interactions with ct46.

Figure 1