How is cell cycle control different between the germ line and soma? We isolated a strong temperature-sensitive allele of the
emb-30 locus (Cassada et al., Dev. Biol. 84: 193-205, 1981),
tn377 ts III, that blocks the meiotic divisions and germline proliferation.
emb-30 mutant oocytes undergo normal nuclear envelope breakdown, ovulation, and fertilization. They are able to set up a meiotic spindle but apparently do not progress through meiotic M-phase. As a result, no polar bodies are produced, pronuclei do not form, and embryonic development does not occur. If
emb-30 (
tn377 ts) mutant embryos are shifted to the non-permissive temperature, they grow into sterile adults. This Sterile phenotype results when Z2 and Z3 block during mitosis of their first attempted division during the L1 larval stage. By contrast, somatic development is apparently normal. When
emb-30 (
tn377 ts) adults are shifted to the non-permissive temperature, mitotic germ cells accumulate in the distal mitotic zone. Thus,
emb-30 is likely to be required continually for completion of germline mitosis. We isolated 14 additional alleles in unbiased non-complementation screens. The strongest alleles are Sterile/Evl and appear to significantly reduce or eliminate
emb-30 gene function by genetic and molecular criteria. Further analysis of the new alleles suggests that
emb-30 has both germline and somatic functions and that the germline functions are separately mutable. Genetic mapping placed
emb-30 within the
emb-9 -
sod-4 interval. A left boundary was provided by the deficiency tnDf2 that fails to complement
emb-30 and genes on its right (e.g.
ced-7 and
sqv-3 ), but complements
emb-9 . We localized the left breakpoint of tnDf2 to the cosmid T26G10. RNAi directed against a predicted gene from an adjacent cosmid (F54C8) resulted in an identical one cell arrest phenotype seen in several
emb-30 alleles. Therefore,
emb-30 appears to encode a novel 117 kdal protein. This identification was confirmed by sequencing the 15 chemically generated
emb-30 alleles. The sequence of the
emb-30 mutant alleles identifies residues that are critical for
emb-30 function.