Abstract
Elastic “tethers” connect separating anaphase chromosomes in most (or all) animal cells. We tested whether tethers are involved in coordinating movements of separating anaphase chromosomes in crane-fly spermatocytes. In these cells the coupled movements of separating chromosomes become uncoupled after the tethers are severed by laser microbeam irradiation of the interzone region between the chromosomes (Sheykhani et al., 2017). While this strongly suggests that tethers are involved with coordinating the poleward chromosome movements, the experiments are open to another interpretation: laser irradiations that cut the tethers also might damage something else in the interzone, and those non-tether components might regulate chromosome movements. In the experiments reported herein we distinguish between those two possibilities by disabling the tethers without cutting the interzone. We cut the arms from individual chromosomes, thereby severing the mechanical connection between separating chromosomes, disconnecting them, without damaging components in the interzone. Disabling tethers in this way uncoupled the movements of the separating chromosomes. We thus conclude that tethers are involved in regulating the speeds of separating anaphase chromosomes in crane-fly spermatocytes.
Highlights
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 animal cell spindles (Forer et al, 2017; Paliulis and Forer, 2018)
Elastic Tethers Between Separating Telomeres is deduced by severing chromosome arms during anaphase, after which the resultant arm fragments move across the equator, led by their telomeres, until they reach their partner telomeres (LaFountain et al, 2002; Sheykhani et al, 2017)
Summary
This article deals with possible functions of “tethers,” elastic connections between anaphase chromosomes. UV microbeam irradiations of anaphase kinetochore spindle fibres can sever microtubules and they can stop chromosome movements, depending on the UV wavelength, effects which occur independently of each other These experiments indicated that chromosome movements are coupled, as follows. Since severing the tether removes the “prohibition” on acceleration, this result suggests that tethers that connect separating telomeres are involved in regulating speeds of separating chromosomes This important conclusion has a possible flaw, though, because laser irradiation of the interzone that severs the tethers may cause collateral damage to other interzonal components and these other components may coordinate the movements of the partner chromosomes. The associated chromosomes accelerated after their kinetochore fibres were severed, implicating tethers in the regulation of poleward speeds of separating anaphase chromosomes in crane-fly spermatocytes
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