The CENP-F-like proteins HCP-1 and HCP-2 target CLASP to kinetochores to mediate chromosome segregation.
During chromosome segregation, kinetochores form dynamic connections with spindle microtubules. In vertebrates, these attachments require the activities of a number of outer kinetochore proteins, including CENP-F [1, 2] and the widely conserved microtubule-associated protein CLASP [3]. Here, we investigate the functional relationship between HCP-1/2, two redundant CENP-F-like proteins, and CLASP(CLS-2) in Caenorhabditis elegans. HCP-1/2 and CLASP(CLS-2) localize transiently to mitotic C. elegans kinetochores with nearly identical kinetic profiles, and biochemical purifications demonstrate that they also associate physically. In embryos depleted of HCP-1/2, CLASP(CLS-2) no longer localizes to chromosomes, whereas CLASP(CLS-2) depletion does not prevent HCP-1/2 targeting. Consistent with the localization dependency and biochemical association, depletion of HCP-1/2 or CLASP(CLS-2) resulted in virtually identical defects in mitotic chromosome segregation characterized by a failure of sister-chromatid biorientation. This phenotype could be partially suppressed by disrupting the astral forces that pull spindle poles apart in the 1 cell embryo, indicating that CLASP(CLS-2) is required for biorientation when chromosome-spindle attachments are subjected to poleward force. Our results establish that the key role of HCP-1/2 is to target CLASP(CLS-2) to kinetochores, and they support the recently proposed model that CLASP functions to promote the polymerization of kinetochore bound microtubules [4].
Cheeseman
Iain M
IM
Department of Cellular and Molecular Medicine, Ludwig Institute for Cancer Research, University of California, San Diego School of Medicine, La Jolla, 92093, USA. icheeseman@ucsd.edu
MacLeod
Ian
I
Yates
John R
JR
Oegema
Karen
K
Desai
Arshad
A
D000818:Animals; D015153:Blotting, Western; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D020090:Chromosome Segregation / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D018386:Kinetochores / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D034622:RNA Interference; D008941:Spindle Apparatus / Q000378:metabolism*
D029742:Caenorhabditis elegans Proteins; D002868:Chromosomal Proteins, Non-Histone; C400273:HCP-2 protein, C elegans; D008869:Microtubule-Associated Proteins; C400272:hcp-1 protein, C elegans