Malorientation in half-bivalents at anaphase: analysis of autosomal laggards in untreated, cold-treated, and cold-recovering crane fly spermatocytes.

Abstract

Exposing crane fly larvae to 6.degree. C or returning them to 22.degree. C after exposure to 6.degree., 2.degree. or 0.2.degree. C can induce any number of autosomes in their primary spermatocytes to lag near the spindle equator at anaphase. Autosomal laggards in cold-recovering cells are contained in bivalents until anaphase (Janicke, M.A., and J.R. LaFountain, 1982). Documentation that lagging autosomes in cold-treated and cold recovering cells are maloriented is reported. During meiosis I, half-bivalents usually associated with only one pole via kinetochore fibers, with sister chromatids being oriented to the same pole. Laggards had kinetochore microtubules (kMT) extending from them toward both poles: 1 sister was oriented to 1 pole and the other hand some or all of its kMT extending toward the opposite pole. Bipolar malorientation of autosomal laggards was observed 1 untreated cell. The number of kMT per half-bivalent was similar in lagging and non-lagging autosomes, and those kMT were contained on long birefringent kinetochore fibers. The overall spindle structure in cold-recovering cells was similar to that observed in untreated anaphase cells. Giemsa-stained centromeric dots of sister chromatids were contiguous in non-laggards and separated in laggards at anaphase. Bipolar malorientations can probably exist at anaphase in chromosomes that remain paired until anaphase, that cold recovery increases the frequency of that anomaly, and that such malorientations may be 1 cause of anaphase lag.