title: Chromosome malorientations after meiosis II arrest cause nondisjunction.
abstract: This study investigated the basis of meiosis II nondisjunction. Cold arrest induced a fraction of meiosis II crane fly spermatocytes to form (n + 1) and (n - 1) daughters during recovery. Live-cell liquid crystal polarized light microscope imaging showed nondisjunction was caused by chromosome malorientation. Whereas amphitely (sister kinetochore fibers to opposite poles) is normal, cold recovery induced anaphase syntely (sister fibers to the same pole) and merotely (fibers to both poles from 1 kinetochore). Maloriented chromosomes had stable metaphase positions near the equator or between the equator and a pole. Syntelics were at the spindle periphery at metaphase; their sisters disconnected at anaphase and moved all the way to a centrosome, as their strongly birefringent kinetochore fibers shortened. The kinetochore fibers of merotelics shortened little if any during anaphase, making anaphase lag common. If one fiber of a merotelic was more birefringent than the other, the less birefringent fiber lengthened with anaphase spindle elongation, often permitting inclusion of merotelics in a daughter nucleus. Meroamphitely (near amphitely but with some merotely) caused sisters to move in opposite directions. In contrast, syntely and merosyntely (near syntely but with some merotely) resulted in nondisjunction. Anaphase malorientations were more frequent after longer arrests, with particularly long arrests required to induce syntely and merosyntely.
authors.affiliation: Department of Biological Sciences, State University of New York at Buffalo, Amherst, NY 14260, USA. mjanicke@buffalo.edu
authors.forename: Marie A
authors.initials: MA
authors.lastname: Janicke
authors.forename: Loren
authors.initials: L
authors.lastname: Lasko
authors.forename: Rudolf
authors.initials: R
authors.lastname: Oldenbourg
authors.forename: James R
authors.initials: JR
authors.lastname: LaFountain
mesh_terms: D000818:Animals; D002842:Chromatids / Q000648:ultrastructure; D003080:Cold Temperature / Q000009:adverse effects; D004175:Diptera / Q000235:genetics / Q000648:ultrastructure; D008297:Male; D008540:Meiosis / Q000235:genetics*; D008957:Models, Genetic; D009630:Nondisjunction, Genetic; D013091:Spermatogenesis / Q000235:genetics