A review of “tethers”: elastic connections between separating partner chromosomes in anaphase

Abstract

Recent work has demonstrated the existence of elastic connections, or tethers, between the telomeres of separating partner chromosomes in anaphase. These tethers oppose the poleward spindle forces in anaphase. Functional evidence for tethers has been found in a wide range of animal taxa, suggesting that they might be present in all dividing cells. An examination of the literature on cell division from the nineteenth century to the present reveals that connections between separating partner chromosomes in anaphase have been described in some of the earliest observations of cell division. Here, we review what is currently known about connections between separating partner chromosomes in anaphase, and we speculate on possible functions of tethers, and on what they are made of and how one might determine their composition.

Anaphase Chromosomes in Crane-Fly Spermatocytes Treated With Taxol (Paclitaxel) Accelerate When Their Kinetochore Microtubules Are Cut: Evidence for Spindle Matrix Involvement With Spindle Forces

“…Aspects of our experiments peripheral to how force is produced with severed kinetochore microtubules deal with further evidence that elastic “tethers” cause the movements of arm fragments (cut from telomere-containing ends of anaphase chromosomes) toward their separating partner chromosomes (across the equator). The experimental evidence that these movements are due to elastic tethers that extend between chromosomes and not to interzonal microtubules (discussed in LaFountain et al, 2002 ; Forer et al, 2017 ; Paliulis and Forer, 2018 ) basically is that arm-fragment movement stops after ablation of either the moving telomere or the partner′s telomere (to which the fragment is moving). Our results on movements of arm fragments in taxol-treated cells add to this argument because taxol-treatment eliminates the transport properties of crane-fly spermatocyte spindle microtubules: akinetic pieces of chromosomes in not- treated crane-fly spermatocytes move poleward, but akinetic pieces in taxol-treated spermatocytes do not move poleward, showing that the non-dynamic spindle microtubules in taxol-treated cells no longer support their movement (LaFountain et al, 2001 ).…”

Evidence of Non-microtubule Spindle Forces in Mesostoma ehrenbergii Spermatocytes

“…To test the role of tethers we disabled them directly by cutting a section from the tip of a free arm [ Figure 2B , Laser experiment]; this disconnects the mechanical connection between the arms and hence to the kinetochore to which it originally was attached. Since tethers cannot be visualized, one needs to cut arms to test if an elastic tether is present ( Paliulis and Forer, 2018 ). If elastic tethers are present, the arm fragment moves to the partner telomere ( LaFountain et al, 2002 ), as illustrated in the cartoon in Figure 2B .…”

Elastic Tethers Between Separating Anaphase Chromosomes Regulate the Poleward Speeds of the Attached Chromosomes in Crane-Fly Spermatocytes

“…One could expand the experimental repertoire if one could identify tethers in living or stained cells. The literature from the early 1900s illustrates stained strands that connect the arms of separating anaphase chromosomes and therefore appear to be tethers ( Paliulis and Forer, 2018 ). That the connecting material is different from spindle fibres themselves is especially clear in Figure 11 of Cleland (1926) because the chromosomes in Oenothera meiosis are a series of reciprocal translocations ( Hejnowicz and Feldman, 2000 ) with separating anaphase telomeres at an angle to the spindle axis: the stained strands connecting the telomeres in Oenothera are also at an angle to the spindle axis and therefore most likely represent tethers.…”

“…This article deals with possible functions of “tethers,” elastic connections between anaphase chromosomes. Tethers extend between the telomeres of all pairs of separating anaphase chromosomes in all (or most) animal cell spindles ( Forer et al, 2017 ; Paliulis and Forer, 2018 ). One cannot identify tethers using phase-contrast or DIC microscopy, however.…”

“…Tethers are universally present in animal cells, connecting all separating chromosome pairs ( Paliulis and Forer, 2018 ). They also seem to be present in plant cells, as judged by stained connections between anaphase telomeres ( Cleland, 1926 ), though there have been no experiments on plant cells to see if arm fragments move.…”