Worm Breeder's Gazette 11(3): 64
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 screening for maternal effect sterile (mes) mutations ( WBG 10(3):101) in an attempt to identify maternally encoded factors required for germ line development. Using an F3 screen for sterile animals, we have screened 7200 haploid genomes and identified 8 alleles. These fall into five complementation groups (see Table 1) and all are strict maternal effect mutations. We predicted that at least two classes of mutations might be identified: 1) mutations in genes that encode factors required for the determination, establishment or maintenance of the germ line and 2) par-like mutations that affect cytoplasmic localization of maternal factors ( Cell 52: 311). Of the mes loci that have been analyzed, three appear to belong to the first class while one may affect partitioning of germ line determinants. [See Figure 1] mes-1 is likely to affect the cellular partitioning machinery. All four alleles of mes-1 are temperature sensitive and incompletely expressed; homozygous mothers produce both sterile and fertile progeny. In addition, all alleles show some mis-segregation of P granules in L1 progeny of homozygous mutant mothers. This suggests that the mes-1 gene product is involved in a temperature-sensitive process that affects partitioning of cytoplasmic components. However, mes-1, unlike previously described partitioning mutations, has fairly low embryonic lethality. [See Figure 2] mes-2, mes-3 and mes-1 may affect germ-line-specific factors. The remaining three complementation groups show normal P-granule segregation to Z2 and Z3 in L1 offspring of homozygous mutant mothers and exhibit no significant embryonic lethality. mes-2(bn11) adult sterile progeny and mes-3(bn21ts) adult sterile progeny raised at the non-permissive temperature lack a germ line (assayed by DAPI staining). mes-4(bn23) adult sterile progeny contain approximately 20 mitotic germ nuclei per gonad arm. All sterile animals have a somatic gonad. Maternal effect sterility may be the null phenotype for mes-3 since hermaphrodites of the genotype mes-3(bn35)/sDf4, a deficiency that deletes the locus, produce all sterile progeny. We feel that these mutations are good candidates for maternal factors required for germ line development because 1) lineage-specific cytoplasmic factors appear to be segregated normally and 2) the mutant defect is specific to the germ line of the progeny of mutant mothers. mes-3 and mes-4 map genetically to regions containing contigs and we are focussing on cloning these genes.