Worm Breeder's Gazette 13(3): 28 (June 1, 1994)

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.


Cathy Caron, Kenneth Kemphues, Cornell University, Ithaca. New York.

zyg-1 mutations show a maternal effect on the early cleavages of the C. elegans embryo (1,2), as well as a zygotic effect on the formation of the vulva. In embryos from homozygous mutant mothers, the first mitotic division appears normal, but although the AB and P1 cell nuclei break down at the appropriate time, no spindles form and the cells fail to divide. During the next hour, the blastomeres exhibit extensive cortical contractions and cytoplasmic rearrangements and become very irregularly shaped. The abnormal nuclei in these cells continue to break down at regular intervals, and the time between one nuclear breakdown and the next is shorter for the AB nucleus than for the P1 nucleus, as in wild type. This suggests that at least some aspects of the normal cell cycle are still functioning in zyg-1 embryos. After approximately one hour, cells of variable sizes and DNA contents begin to form, and the embryos eventually arrest with less than 50 cells. Immunofluorescence with anti-tubulin antibodies has shown a variety of abnormalities, including both multipolar spindles and monoastral mitotic cells. In general, there are fewer asters in zyg-1 embryos than in wild type embryos of the same age and DNA content, suggesting that the centrosomes may either not be replicating or that some may not be functional.

In addition to this embryonic phenotype, four out of five of the zyg-1 alleles show an egg laying defective (Egl) phenotype at 25°, although none are fully penetrant. All five alleles show an increased penetrance of this Egl phenotype when heterozygous with ccDf5 ,a deficiency which deletes zyg-1 .My preliminary analysis suggests that this defect is due to structural changes in the vulva, and I am in the process of determining whether this is due to a failure of cell divisions similar to that in embryos. The temperature sensitive period for the allele zyg-1 ( it25ts )is at the L2 /L3boundary (25 to 26 hours after hatching), which is when the fates of the vulval precursor cells are determined. This suggests that zyg-1 may act at this time to prepare these cells for the subsequent divisions. Our current hypothesis is that zyg-1 is needed to produce or maintain functional centrosomes, and is used specifically in the early embryo and in the vulval precursor cells.

I have also initiated a molecular analysis to further clarify the role of zyg-1 in these cell divisions. zyg-1 is between clr-1 and lin-4 on chromosome II, and is deleted by ccDf5 .Using transformation rescue, I have determined that zyg-1 is contained in a 4 kb piece of the cosmid C08D10 .I expect to begin sequencing a cDNA corresponding to zyg-1 very soon.

Literature Cited:

1) Vanderslice and Hirsh, Developmental Biology, 49, 236-249.

2. Kemphues et al., Genetics, 120, 977-986.