Worm Breeder's Gazette 10(3): 101
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.
Several types of embryo manipulation experiments suggest that cell fates are specified in early C. elegans embryos mainly by internally segregated maternal factors. The defects in intestinal cell differentiation and germ-line development observed in some of the par ( for partitioning) mutants strengthen this view for the intestine and germ-line (Kemphues et al. Cell 52, 311-320, 1988). We have begun screening for mutations in the maternal factors required for development of the germ line. We are screening for maternal effect sterile (mes) or grandchildless mutants by looking among EMS- mutagenized worms for the production of sterile progeny in the F3 generation, as shown below: [See Figure 1] We expect to identify at least 2 classes of mutants 1) par mutants and 2) germ-line determinant mutants. One mes locus, identified by the two mutant alleles, bn7 and bn24, exhibits par like qualities. Both alleles are strict maternal effect and, like Dar-2(e2030), are leaky -- homozygous bn7 and bn24 hermaphrodites produce some fully fertile and some sterile, agametic progeny. Similar to par-2(e2030), some embryos from bn7 and bn24 hermaphrodites show aberrant partitioning of germ-line P granules to somatic founder cells during the divisions of P2 and P3 -- we do not know whether the mis- distribution of P granules leads to sterility. There is some elevation in lethality of the embryos produced by bn7 and bn24 hermaphrodites, especially at 25 C -- 14% lethality for bn7 embryos compared to 6% for N2 embryos and 45% for par-2(e2030) embryos at 25 C. bn7 and bn24 are not alleles of the known par loci -- they map to the X chromosome, in the vicinity of lin-2 and unc-9. (Careful mapping is in progress - any new markers in the region would be greatly appreciated!) Two other par-like mes mutants are currently being mapped and analyzed. The mes mutant, bn11, is a good candidate for a germ-line determinant mutant. It is a strict maternal effect mutant that produces 100% sterile, agametic progeny. P granules are segregated normally in embryos from bn11 hermaphrodites -- thus there is no apparent partitioning defect. However, embryonic lethality is somewhat elevated (12%) at 25 C. bn11 maps to LGII, approx. 18 map units to the right of unc-4, probably out in the big bare zone between rol-1 and unc-52 (again, any new markers on the right arm of LGII would be welcome) - LGII does not contain any of the known par loci. In addition to bn11, one other fully penetrant mes mutant is being mapped and analyzed.