Worm Breeder's Gazette 14(5): 51 (February 1, 1997)
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.
|1||Section of Genetics and Development, Cornell University, Ithaca, NY 14853.|
|2||CRBM- CNRS Montpellier, France.|
zyg-9 is a maternal effect gene required for cytoplasmic organization and microtubule function in the one-cell embryo. Mutations in zyg-9 result in disorganized meiotic spindles, failure of pronuclear migration, and a mitotic spindle that contains abnormally short astral microtubules. The mitotic spindle forms around the male pronucleus and fails to rotate resulting in an aberrant cleavage division. We have previously reported the cloning and initial molecular characterization of zyg-9. A Blast search revealed similarity between ZYG-9 and the human ch-TOG protein, the S. pombe p93DIS1 protein, and the STU2 protein of S. cerevisiae. ch-TOG shares 48% amino acid identity with a 230 residue domain which is tandemly repeated at the N-terminus of ZYG-9 (51% amino acid identity between repeats). p93DIS1 and STU2 are 32 % and 20 % identical to a region of ~160 AA within the same domain of ZYG-9. The function of this domain is unknown. ch-TOG also exhibits 40% identity with a second domain of ~250 amino acids within ZYG-9. The function of the ch-TOG gene is unknown, although it is over expressed in certain tumor cell lines (1) and its expression is higher in dividing cells than in quiescent cells. The product of the p93DIS1 gene, which is required for sister chromatid separation, localizes to the spindle pole body during mitosis (2). We have generated antibodies against 461 amino acids at the carboxy terminal end of ZYG-9 and shown that purified antiserum recognizes a protein of ~156 kD, the predicted size of ZYG-9, in wild type embryos. This protein is not seen in embryos of three of seven zyg-9 alleles examined. Immunofluorescence microscopy has revealed that ZYG-9 protein localizes to both the meiotic and mitotic spindles. It also localizes to the peripheral region of the poles of the embryo throughout meiosis. At metaphase and anaphase of meiosis I, ZYG-9 colocalizes with tubulin in the meiotic spindle, although its distribution is more diffuse than that of tubulin. Unlike tubulin, ZYG-9 localizes more intensely at the meiotic spindle poles. A similar pattern of localization is observed during meiosis II, although peripheral staining at the poles of the embryo is less pronounced. At the onset of the first mitotic division, ZYG-9 localizes to the newly duplicated centrosomes. Centrosomal localization persists throughout mitosis. Between late prometaphase and early anaphase ZYG-9 also localizes to the kinetochore region. This pattern of localization is observed in all mitotic cells in the developing embryo and in the mitotic cells of the gonad. Localization of ZYG-9 protein to the centrosome may be essential for the formation of the unusually long astral microtubules present in the mitotic spindle of the 1-cell embryo. References: 1.) Charasse, S., Mazel, M., Taviaux, S., Berta, P., Chow, T., and Larroque, C. (1993). Eur. J. Biochem. 243:406-413 2.) Nakaseko Y., Nabeshima K., Kinoshita K. And Yanagida M., (1996) Genes to Cells 1:633-644