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J. Cell Biol.,
Volume 145, Number 3, May 3, 1999 425-435
* Department of Botany and We have identified a maize homologue of
yeast MAD2, an essential component in the spindle
checkpoint pathway that ensures metaphase is complete before anaphase begins. Combined immunolocalization of MAD2 and a recently cloned maize CENPC
homologue indicates that MAD2 localizes to an outer
domain of the prometaphase kinetochore. MAD2
staining was primarily observed on mitotic kinetochores that lacked attached microtubules; i.e., at
prometaphase or when the microtubules were depolymerized with oryzalin. In contrast, the loss of MAD2
staining in meiosis was not correlated with initial microtubule attachment but was correlated with a measure of
tension: the distance between homologous or sister kinetochores (in meiosis I and II, respectively). Further,
the tension-sensitive 3F3/2 phosphoepitope colocalized,
and was lost concomitantly, with MAD2 staining at the
meiotic kinetochore. The mechanism of spindle assembly (discussed here with respect to maize mitosis and
meiosis) is likely to affect the relative contributions of
attachment and tension. We support the idea that
MAD2 is attachment-sensitive and that tension stabilizes microtubule attachments.
Department of Genetics, University of Georgia, Athens, Georgia 30602; § Pioneer Hi-Bred
International, Inc., Johnston, Iowa 50131
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