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Forer A, Otsuka S. Structural evidence for elastic tethers connecting separating chromosomes in crane-fly spermatocytes. Life Sci Alliance 2023; 6:e202302303. [PMID: 37591724 PMCID: PMC10435969 DOI: 10.26508/lsa.202302303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Revised: 08/06/2023] [Accepted: 08/07/2023] [Indexed: 08/19/2023] Open
Abstract
Different types of anaphase bridges are reported to form between segregating chromosomes during cell division. Previous studies using laser microsurgery suggested that elastic tethers connect the telomeres of separating anaphase chromosomes in many animal meiotic and mitotic cells. However, structural evidence is lacking for their existence. In this study, by correlating live imaging with electron tomography, we examined whether visible structures connect separating telomeres in meiosis I of crane-fly primary spermatocytes. We found structures extending between separating telomeres in all stages of anaphase. The structures consist of two components: one is darkly stained, looking somewhat like chromatin, whereas the other is more lightly stained, appearing filamentous. Although in early anaphase both structures extend between telomeres, in later anaphase, the darker structure extends shorter distances from the telomeres but the lighter structure still extends between the separating telomeres. From these observations, we deduced that these structures represent the "tethers" inferred from the laser-cutting experiments. Because elastic tethers have been detected in a variety of animal cells, they probably are present during anaphase in all animal cells.
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Affiliation(s)
- Arthur Forer
- Biology Department, York University, North York, Canada
| | - Shotaro Otsuka
- Max Perutz Labs, Vienna Biocenter Campus, Vienna, Austria
- Medical University of Vienna, Center for Medical Biochemistry, Vienna, Austria
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Forer A, Adil A, Berns MW. Blocking Protein Phosphatase 1 [PP1] Prevents Loss of Tether Elasticity in Anaphase Crane-Fly Spermatocytes. Front Mol Biosci 2021; 8:636746. [PMID: 34169091 PMCID: PMC8218814 DOI: 10.3389/fmolb.2021.636746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Accepted: 04/16/2021] [Indexed: 11/24/2022] Open
Abstract
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.
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Affiliation(s)
- Arthur Forer
- Biology Department, York University, Toronto, ON, Canada
| | - Aisha Adil
- Biology Department, York University, Toronto, ON, Canada
| | - Michael W Berns
- Beckman Laser Institute, University of California, Irvine, Irvine, CA, United States.,Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, United States.,Department of Surgery, University of California, Irvine, Irvine, CA, United States.,Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, United States.,Department of Bioengineering, University of California, San Diego, San Diego, CA, United States.,Institute of Engineering in Medicine, University of California, San Diego, San Diego, CA, United States
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