Regulación molecular de la segregación cromosómica

Kinetochore-Independent Chromosome Poleward Movement during Anaphase of Meiosis II in Mouse Eggs
Manqi Deng*, Juntao Gao, Praveen Suraneni, Rong Li*
Stowers Institute for Medical Research, Kansas City, Missouri, United States of America

Abstract
Kinetochores are considered to be the key structures that physically connect spindle microtubules to the chromosomes and play an important role inchromosome segregation during mitosis. Due to different mechanisms of spindle assembly between centrosome-containing mitotic cells and acentrosomal meiotic oocytes, it is unclear how a meiotic spindle generates the poleward forces to drive two rounds of meiotic chromosome segregation to achieve genome haploidization. We took advantage of the fact that DNA beads are able to induce bipolar spindleformation without kinetochores and studied the behavior of DNA beads in the induced spindle in mouse eggs during meiosis II. Interestingly, DNA beads underwent poleward movements that were similar in timing and speed to the meiotic chromosomes, although all the beads moved together to the same spindle pole. Disruption of dynein function abolished the poleward movements of DNA beads but not of themeiotic chromosomes, suggesting the existence of different dynein-dependent and dynein-independent force generation mechanisms for the chromosome poleward movement, and the latter may be dependent on the presence of kinetochores. Consistent with the observed DNA bead poleward movement, sperm haploid chromatin (which also induced bipolar spindle formation after injection to a metaphase egg withoutforming detectable kinetochore structures) also underwent similar poleward movement at anaphase as DNA beads. The results suggest that in the chromatin-induced meiotic spindles, kinetochore attachments to spindle microtubules are not absolutely required for chromatin poleward movements at anaphase.
Citation: Deng M, Gao J, Suraneni P, Li R (2009) Kinetochore-Independent Chromosome PolewardMovement during Anaphase of Meiosis II in Mouse Eggs. PLoS ONE 4(4): e5249. doi:10.1371/journal.pone.0005249 Editor: Kevin G. Hardwick, University of Edinburgh, United Kingdom Received November 19, 2008; Accepted March 22, 2009; Published April 13, 2009 Copyright: ß 2009 Deng et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permitsunrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Funds from Stowers Institute for Medical Research to RL. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail:MQD@stowers-institute.org (MD); RLI@stowers-institute.org (RL)

Introduction
Accurate chromosome segregation during eukaryotic cell division is achieved by a microtubule-based bipolar spindle which generates forces to move the replicated chromosomes toward opposite poles. It has been a long standing question how spindle microtubules (as well as the associated motor molecules) generate the polewardforces to segregate chromosomes during cell division. Although the detailed molecular mechanisms are still not completely understood, it is generally accepted that the kinetochore, a proteinaceous structure assembled at the chromosomal centromere region, plays important roles in chromosome segregation [1,2,3,4,5,6,7]. The kinetochore mediates the physical interactions between a replicatedchromosome and microtubules to establish a biorientation configuration during metaphase and ensure accurate segregation during anaphase [4,5,8,9,10]. The kinetochore-connected microtubules, or K-fibers, are thought to apply the poleward forces to the chromosomes and pull chromosomes toward the opposing poles during anaphase [11,12,13]. In addition to the forces exerted on the kinetochores, it is known...