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.

The zyg-9 gene encodes a component of the meiotic and mitotic spindles

Lisa Matthews1, Danielle Thierry-Mieg2, Ken Kemphues1

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.

 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