title: Kinetochore-driven outgrowth of microtubules is a central contributor to kinetochore fiber maturation in crane-fly spermatocytes.
abstract: We use liquid crystal polarized light imaging to record the life histories of single kinetochore (K-) fibers in living crane-fly spermatocytes, from their origins as nascent K-fibers in early prometaphase to their fully matured form at metaphase, just before anaphase onset. Increased image brightness due to increased retardance reveals where microtubules are added during K-fiber formation. Analysis of experimentally generated bipolar spindles with only one centrosome, as well as of regular, bicentrosomal spindles, reveals that microtubule addition occurs at the kinetochore-proximal ends of K-fibers, and added polymer expands poleward, giving rise to the robust K-fibers of metaphase cells. These results are not compatible with a model for K-fiber formation in which microtubules are added to nascent fibers solely by repetitive "search and capture" of centrosomal microtubule plus ends. Our interpretation is that capture of centrosomal microtubules-when deployed-is limited to early stages in establishment of nascent K-fibers, which then mature through kinetochore-driven outgrowth. When kinetochore capture of centrosomal microtubules is not used, the polar ends of K-fibers grow outward from their kinetochores and usually converge to make a centrosome-free pole.
authors.affiliation: Department of Biological Sciences, University at Buffalo, Buffalo, NY 14260 Cellular Dynamics Program, Marine Biological Laboratory, Woods Hole, MA 02543 Physics Department, Brown University, Providence, RI 02912.
authors.forename: James R
authors.initials: JR
authors.lastname: LaFountain
authors.forename: Rudolf
authors.initials: R
authors.lastname: Oldenbourg
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D018385:Centrosome / Q000378:metabolism / Q000648:ultrastructure; D004175:Diptera / Q000166:cytology*; D019476:Insect Proteins / Q000378:metabolism; D018386:Kinetochores / Q000502:physiology* / Q000648:ultrastructure; D008297:Male; D008870:Microtubules / Q000378:metabolism; D013090:Spermatocytes / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D019476:Insect Proteins