The role of myosin phosphorylation in anaphase chromosome movement

Adil

Berns

2021

Front. Mol. Biosci.

Self Cite

In normal anaphase cells, telomeres of each separating chromosome pair are connected to each other by tethers. Tethers are elastic at the start of anaphase: arm fragments cut from anaphase chromosomes in early anaphase move across the equator to the oppositely-moving chromosome, telomere moving toward telomere. Tethers become inelastic later in anaphase as the tethers become longer: arm fragments no longer move to their partners. When early anaphase cells are treated with Calyculin A (CalA), an inhibitor of protein phosphatases 1 (PP1) and 2A (PP2A), at the end of anaphase chromosomes move backward from the poles, with telomeres moving toward partner telomeres. Experiments described herein show that in cells treated with CalA, backwards movements are stopped in a variety of ways, by cutting the tethers of backwards moving chromosomes, by severing arms of backwards moving chromosomes, by severing arms before the chromosomes reach the poles, and by cutting the telomere toward which a chromosome is moving backwards. Measurements of arm-fragment velocities show that CalA prevents tethers from becoming inelastic as they lengthen. Since treatment with CalA causes tethers to remain elastic throughout anaphase and since inhibitors of PP2A do not cause the backwards movements, PP1 activity during anaphase causes the tethers to become inelastic.

Section: Resultsmentioning

confidence: 99%

Blocking Protein Phosphatase 1 [PP1] Prevents Loss of Tether Elasticity in Anaphase Crane-Fly Spermatocytes

Adil

Berns

2021

Front. Mol. Biosci.

Self Cite

“…Another, chromator , is implicated in spindle function in that chromosome movement was perturbed after either depletion of chromator by RNAi or by direct mutation of the chromator gene (Rath et al, 2004 ; Ding et al, 2009 ). Myosin and actin involvement in force production, and perhaps association with the spindle matrix (Johansen et al, 2011 ), is indicated by a variety of experiments including both pharmacological and molecular genetic approaches (discussed in Pickett-Heaps and Forer, 2009 ; Sheykhani et al, 2013 ; Mogessie and Schuh, 2017 ). It still is not clear what the spindle matrix is composed of, how it acts, and how actin and myosin might interact with chromator or other matrix components (e.g., Johansen et al, 2011 ), so it is difficult to know how the forces from the spindle matrix are produced.…”

Section: Discussionmentioning

confidence: 99%

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

Sheykhani

Berns

2018

Front. Cell Dev. Biol.

Self Cite

Various experiments have indicated that anaphase chromosomes continue to move after their kinetochore microtubules are severed. The chromosomes move poleward at an accelerated rate after the microtubules are cut but they slow down 1–3 min later and move poleward at near the original speed. There are two published interpretations of chromosome movements with severed kinetochore microtubules. One interpretation is that dynein relocates to the severed microtubule ends and propels them poleward by pushing against non-kinetochore microtubules. The other interpretation is that components of a putative “spindle matrix” normally push kinetochore microtubules poleward and continue to do so after the microtubules are severed from the pole. In this study we distinguish between these interpretations by treating cells with taxol. Taxol eliminates microtubule dynamics, alters spindle microtubule arrangements, and inhibits dynein motor activity in vivo. If the dynein interpretation is correct, taxol should interfere with chromosome movements after kinetochore microtubules are severed because it alters the arrangements of spindle microtubules and because it blocks dynein activity. If the “spindle matrix” interpretation is correct, on the other hand, taxol should not interfere with the accelerated movements. Our results support the spindle matrix interpretation: anaphase chromosomes in taxol-treated crane-fly spermatocytes accelerated after their kinetochore microtubules were severed.

“…Another possibility for producing force in the absence of microtubules is actin and myosin. Actin and myosin have been identified as being present in large numbers of spindles (Forer et al 2003, Table 1) and physiological data support actin and myosin being involved in spindle function (e.g., Mogessie and Schuh, 2017;Sheykhani et al 2013aSheykhani et al , 2013b. Another possibility is the 'spindle matrix' (e.g., Johansen and Johansen, 2007;Pickett-Heaps and Forer, 2009).…”

Section: Chromosome Movement After Addition Of Noc or Colcemidmentioning

confidence: 93%

“…Consideration of actin-myosin and spindle matrix are not mutually exclusive since, as discussed in detail in Johansen et al (2011), the spindle matrix includes proteins such as the nuclear derived proteins Skeletor, Megator, Chromator and EAST and muscle proteins such as actin, myosin, and titin, that colocalize or align with the microtubule spindle in a variety of different cells types (Johansen and Johansen, 2007;Johansen et al 2011). In crane-fly spermatocytes, for example, actin, phosphorylated myosin, and titin are aligned along kinetochore microtubules (Fabian et al, 2007;Sheykhani et al 2013b), in close proximity to spindle matrix proteins (Fabian et al 2007). Just as the spindle matrix 'framework' of a spindle shape remains after removal of spindle microtubules (Johansen and Johansen, 2007;Yao et al 2012), and slowly disappears, the actin 'spindle' that remains after microtubules in mouse meiotic spindles are depolymerised with NOC also seems to slowly disappear (Mogessi and Schuh, 2017, Figure S2B).…”

Section: Chromosome Movement After Addition Of Noc or Colcemidmentioning

confidence: 99%

Chromosomes selectively detach at one pole and quickly move towards the opposite pole when kinetochore microtubules are depolymerized in Mesostoma ehrenbergii spermatocytes

Fegaras

2018

Protoplasma

Self Cite

In a typical cell division, chromosomes align at the metaphase plate before anaphase commences. This is not the case in Mesostoma spermatocytes. Throughout prometaphase, the three bivalents persistently oscillate towards and away from either pole, at average speeds of 5-6 μm/min, without ever aligning at a metaphase plate. In our experiments, nocodazole (NOC) was added to prometaphase spermatocytes to depolymerize the microtubules. Traditional theories state that microtubules are the producers of force in the spindle, either by tubulin depolymerizing at the kinetochore (PacMan) or at the pole (Flux). Accordingly, if microtubules are quickly depolymerized, the chromosomes should arrest at the metaphase plate and not move. However, in 57/59 cells, at least one chromosome moved to a pole after NOC treatment, and in 52 of these cells, all three bivalents moved to the same pole. Thus, the movements are not random to one pole or other. After treatment with NOC, chromosome movement followed a consistent pattern. Bivalents stretched out towards both poles, paused, detached at one pole, and then the detached kinetochores quickly moved towards the other pole, reaching initial speeds up to more than 200 μm/min, much greater than anything previously recorded in this cell. As the NOC concentration increased, the average speeds increased and the microtubules disappeared faster. As the kinetochores approached the pole, they slowed down and eventually stopped. Similar results were obtained with colcemid treatment. Confocal immunofluorescence microscopy confirms that microtubules are not associated with moving chromosomes. Thus, these rapid chromosome movements may be due to non-microtubule spindle components such as actin-myosin or the spindle matrix.