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Partner telomeres during anaphase in crane-fly spermatocytes are connected by an elastic tether that exerts a backward force and resists poleward motion

¹ Department of Biological Sciences, 657 Cooke Hall, University at Buffalo, Buffalo, NY 14260-1300, USA
² Laboratory for Cell Regulation, Division of Molecular Medicine, Wadsworth Center for Laboratories and Research, New York State Department of Health, PO Box 509, Albany, NY 12201-0509, USA
³ Department of Biomedical Sciences, State University of New York, Albany, NY 12222, USA

^* Author for correspondence (e-mail: jrl{at}buffalo.edu )

Accepted 19 January 2002

As chromosomes move polewards during anaphase in crane-fly spermatocytes, trailing arms commonly stretch backwards for a brief time, as if tethered to their partners. To test that notion, a laser microbeam was used to sever trailing arms and thereby release telomere-containing arm segments (called acentric fragments because they lack kinetochores) from segregating chromosomes. Analysis of the movement of acentric fragments after their release provided clear evidence that previously conjoined partners were indeed tethered at their telomeres and that tethers exerted backward forces that were sufficient to move the fragment across the equator and into the opposite half-spindle. To address concerns that tethers might be artifacts of in vitro cell culture, spermatocytes were fixed in situ, and stretched arms within fixed cells provided strong evidence for tethers in vivo. The substantial resistance that tethers impose on the poleward movement of chromosomes must normally be over-ridden by the poleward `pulling' forces exerted at kinetochores. In spermatocytes, poleward forces are supplied primarily by the `traction fibers' that are firmly attached to kinetochores through end-on attachments to the plus ends of kinetochore microtubules.

Key words: Meiosis, Anaphase, Spindle, Chromosomes, Telomeres, Kinetochores, Laser, Microbeam

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