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°C or returning them to 22°C after exposure to 6, 2, or 0 .2°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, Chromosoma, 85 :619-631) . We report here documentation that lagging autosomes in cold-treated and coldrecovering cells are maloriented . During meiosis I, half-bivalents usually associate with only one pole via kinetochore fibers, with sister chromatids being oriented to the same pole. In contrast, laggards had kinetochore microtubules (kMTs) extending from them toward both poles : one sister was oriented to one pole and the other had some or all of its kMTs extending toward the opposite pole. Bipolar malorientation of autosomal laggards also was observed in one untreated cell. The number of kMTs per half-bivalent was similar in lagging and nonlagging autosomes, and those kMTs were contained in 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 nonlaggards and separated in laggards at anaphase . We conclude that bipolar malorientations can 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 one cause of anaphase lag.During the reduction division of meiosis, homologues usually pair to form bivalents . Sister chromatids of one homologue (half-bivalent) become oriented (via a kinetochore fiber) to one spindle pole, and the sister chromatids of its partner homologue both become oriented to the opposite pole. This orientation is thought to cause the bivalent to be subjected to bipolar forces that (a) result in its congression to the metaphase plate, and (b) ensure that upon its separation into halfbivalents at anaphase onset, the coupled sister chromatids of one half-bivalent move together to one pole while the partner half-bivalent moves to the opposite pole (13,29) . In reductiondivision chromosomes that do not pair or become unpaired before anaphase (univalents), sister chromatids may become oriented to opposite poles (25,29) . Univalents with such orientations may congress and then "lag" (see Materials and Methods for terminology) near the spindle equator at anaphase . Laggards may or may not eventually move poleward, and several routes exist by which lagging may lead to the THE fOURNAL OF CELL BIOLOGY " VOLUME 98 MARCH 1984 859-869 ® The Rockefeller University Press " 0021-9525/84/03/0869/11 $1 .00

Checkpoint control in crane-fly spermatocytes: unattached chromosomes induced by cytochalasin D or latrunculin treatment do not prevent or delay the start of anaphase

“…One reason we believe that the bivalents we described as "unattached" are indeed unattached is that when a variety of treatments of crane-fly spermatocytes induce maloriented bivalents (including partial merotely -individual half-bivalent kinetochores being oriented to both poles), the maloriented bivalents become aligned at the equator at metaphase; unlike those described herein, the maloriented bivalents remain in the spindle and do not move to the poles or into the cytoplasm (Janicke and LaFountain 1982, 1984, 1986Ladrach and LaFountain 1986;LaFountain 1985a, b). Another reason is that it is difficult to imagine how bivalents situated partially (Fig.…”

“…An anaphase-onset checkpoint would seem to exist in crane-fly spermatocytes because anaphase does not begin until the 3 autosomal bivalents and 2 sex chromosomes reach the equator (e.g., Dietz 1956Dietz , 1969Dietz , 1972Forer 1980;Janicke and LaFountain 1982): in non-treated cells in which only one sex chromosome, or one bivalent, is slow to reach the equator, anaphase starts only after that last chromosome reaches the equator.…”

Kinetochore microtubules in crane‐fly spermatocytes: Untreated, 2°C‐treated and 6°C‐grown spindles

“…Cell U-6 43 (d) the angles at which they extended through a series of sections [see Janicke and LaFountain, 1984;and LaFountain, 1985b, for examples of tracking kMTs through serial sections in crane-fly spermatocytes] .…”

The Mad1–Mad2 balancing act – a damaged spindle checkpoint in chromosome instability and cancer

“…The presence of kinetochores that are attached to microtubules, but not under tension, also causes the checkpoint to be 'unsatisfied'. These attachments occur naturally during prometaphase, but they can also be induced by the addition and subsequent removal of microtubule-depolymerizing agents from cells (Janicke and LaFountain, 1984;Salmon et al, 2005). Both amphitelic attachment, whereby the system lacks tension, and syntelic attachment, which refers to sister kinetochores that are mono-oriented, lead to an 'unsatisfied' checkpoint ( Fig.…”

“…Chromosomes that are mostly syntelic, but display a small amount of merotelism, could lead to the checkpoint becoming 'unsatisfied' during error correction. However, these kinds of attachments are rare (Janicke and LaFountain, 1984;Salmon et al, 2005).…”