Worm Breeder's Gazette 9(2): 72
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.
We have been studying early cleavage in the worms trying to understand the contributions of the events of cleavage to the regulation of later development. One locus we are concentrating on, par-2 III, has a maternal-effect on the early cleavage pattern and on germ-line function. Recently, we have been screening intensively for new alleles at this locus. Thus far we have a total of four alleles: e2030, it5, it46, and it49. The mutations e2030 and it5 were isolated (e2030 by J. Priess) using the general screen for maternal effect lethal mutations described in an earlier newsletter (vol. 8, #2, p5). The allele it46 was isolated by screening 2,652 chromosomes for failure to complement the grandchildless phenotype of e2030. The allele it49 was isolated in a screen for mel mutations closely linked to daf-7 .u. to the right of daf-7). For the screen, 2452 F1 progeny from crosses of EMS treated daf-7 (e1372 ts); dpy-11 (e224) hermaphrodites X N2 males were cloned at 25 C. Five F2 dauers were picked from each F1 plate and transferred to 16 C. Failure to produce F3 was scored as maternal-effect lethal. The allele it49 was identified as a par-2 allele on the basis of its failure to complement e2030. The range of phenotypes exhibited by these alleles are: 1) Cleavage, up to at least the 3rd division is synchronous. 2) The sizes of AB and P1 cells are nearly equal. 3) The spindles of AB and P1 are always perpendicular to the long axis of the embryo. 4) P granules localize abnormally or not at all. 5) Surviving progeny from homozygous mothers are sterile (i.e. homozygotes are grandchildless). The penetrance of the mutant phenotypes varies among alleles and is dependent upon temperature. it5, it46, and it49 are leaky maternal- effect lethal mutations. The percentages of dead embryos generated by homozygous it46 worms are 99%, 91%, and 90% at 25 C, 20 C, and 16 C respectively. Greater than 99.8% of surviving progeny at all temperatures are sterile. it5 has a more striking temperature effect with 96% lethality at 25 C and 27% at 16 C with 75% of surviving progeny being sterile. The allele e2030 produces a grandchildless phenotype but shows no maternal effect lethality as a homozygote ( Abstracts of 1985 C. elegans meeting, p136). We are now trying to determine the basis for the sterility. Our preliminary results suggest that it is due to an absence or reduction in numbers of germ cells. Temperature shift experiments with it5 demonstrate that the temperature-sensitive period for lethality is between the time of fertilization and the end of the first cleavage. We have not yet determined the TSP for the sterility. These results suggest that the function of par-2 is to insure normal cleavage pattern and cytoplasmic partitioning during early development. Failure in one or both of these processes can lead to death or sterility.