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J. Cell Biol.,
Volume 141, Number 5, June 1, 1998 1159-1168

* Section of Genetics and Development, Cornell University, Ithaca, New York 14850; and We describe the molecular characterization
of zyg-9, a maternally acting gene essential for microtubule organization and function in early Caenorhabditis
elegans embryos. Defects in zyg-9 mutants suggest that
the zyg-9 product functions in the organization of the
meiotic spindle and the formation of long microtubules.
One-cell zyg-9 embryos exhibit both meiotic and mitotic spindle defects. Meiotic spindles are disorganized,
pronuclear migration fails, and the mitotic apparatus
forms at the posterior, orients incorrectly, and contains
unusually short microtubules. We find that zyg-9 encodes a component of the meiotic and mitotic spindle
poles. In addition to the strong staining of spindle
poles, we consistently detect staining in the region of
the kinetochore microtubules at metaphase and early
anaphase in mitotic spindles. The ZYG-9 signal at the
mitotic centrosomes is not reduced by nocodazole treatment, indicating that ZYG-9 localization to the mitotic centrosomes is not dependent upon long astral microtubules. Interestingly, in embryos lacking an organized meiotic spindle, produced either by nocodazole
treatment or mutations in the mei-1 gene, ZYG-9 forms
a halo around the meiotic chromosomes. The protein
sequence shows partial similarity to a small set of proteins that also localize to spindle poles, suggesting a
common activity of the proteins.
Centre de Recherches de Biochimie
Macromoléculaire du Centre National de la Recherche Scientifique, 34293 Montpellier, France
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