Journal
JOURNAL OF CELL BIOLOGY
Volume 172, Issue 1, Pages 19-25Publisher
ROCKEFELLER UNIV PRESS
DOI: 10.1083/jcb.200508180
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Funding
- NIGMS NIH HHS [GM057839, R01 GM057839] Funding Source: Medline
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A family of microtubule (MT)-binding proteins, Orbit/multipleasters/cytoplasmic linker protein -associated protein, has emerged as an important player during mitosis, but their functional mechanisms are poorly understood. In this study, we used meiotic egg extracts to gain insight into the role of the Xenopus laevis homologue Xorbit in spindle assembly and function. Xorbit immunodepletion or its inhibition by a dominant-negative fragment resulted in chromosome alignment defects and aberrant MT structures, including monopolar and small spindles. Xorbit-depleted extracts failed to nucleate MTs around chromatin-coated beads, indicating its essential requirement for spindle assembly in the absence of centrosomes and kinetochores. Xorbit's MT stabilizing effect was most apparent during anaphase, when spindle MTs depolymerized rapidly upon Xorbit inhibition. Biochemical interaction between a COOH-terminal Xorbit fragment and the kinetochore-associated kinesin centromeric protein E may contribute to Xorbit's role in chromosome congression. We propose that Xorbit tethers dynamic MT plus ends to kinetochores and chromatin, providing a stabilizing activity that is crucial for spindle assembly and chromosome segregation.
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