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Fegaras-Arch E, Berns M, Forer A. Evidence of Non-microtubule Spindle Forces in Mesostoma ehrenbergii Spermatocytes. Front Mol Biosci 2020; 7:557990. [PMID: 33330616 PMCID: PMC7711074 DOI: 10.3389/fmolb.2020.557990] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2020] [Accepted: 10/19/2020] [Indexed: 01/04/2023] Open
Abstract
We tested conclusions reached in previous experiments in which Mesostoma spermatocyte chromosomes moved rapidly to a pole in the absence of microtubules: after 10 μM nocodazole (NOC) depolymerized metaphase spindle microtubules, kinetochores from each of the 3 bivalents detached from the same pole and rapidly moved to the other pole, at speeds averaging 37.7 μm/min. with some as high as 100 μm/min. We concluded that these very fast movements were due to non-microtubule forces arising from a spindle matrix. However, since the chromosomes stretch out before detaching, there is tension in the chromosomes from the stretch. Thus the movements of detached kinetochores conceivably might be due to recoil from the tension, though we argued against this possibility (Fegaras and Forer, 2018a). In this article we test whether recoil causes the movements. We cut bivalents into 2 pieces, using a femtosecond laser, before addition of NOC. When 1 bivalent was severed, all kinetochores moved to one pole in 12/15 cells; when 2 bivalents were severed, all kinetochores moved to one pole in 4/6 cells; and when all 3 bivalents were severed all kinetochores moved to one pole in 3/9 cells. The bivalent “halves” moved rapidly, with average speeds of 47 μm/min, velocities that are not significantly different from those in cells without any laser-cut bivalents (p > 0.05). Since kinetochores move at the same speeds whether they are part of bivalents or not, NOC-induced chromosome movements are not due to recoil from tension along the full-length bivalent, strongly supporting the idea that non-microtubule forces move chromosomes in Mesostoma spermatocytes.
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Affiliation(s)
| | - Michael Berns
- Departments of Biomedical Engineering and Cell Biology, Beckman Laser Institute, University of California, Irvine, Irvine, CA, United States.,Institute for Engineering in Medicine and Department of Bioengineering, University of California, San Diego, La Jolla, CA, United States
| | - Arthur Forer
- Department of Biology, York University, Toronto, ON, Canada
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Zakas C, Deutscher JM, Kay AD, Rockman MV. Decoupled maternal and zygotic genetic effects shape the evolution of development. eLife 2018; 7:e37143. [PMID: 30198842 PMCID: PMC6168281 DOI: 10.7554/elife.37143] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Accepted: 09/09/2018] [Indexed: 01/04/2023] Open
Abstract
Evolutionary transitions from indirect to direct development involve changes in both maternal and zygotic genetic factors, with distinctive population-genetic implications, but empirical data on the genetics of such transitions are lacking. The polychaete Streblospio benedicti provides an opportunity to dissect a major transition in developmental mode using forward genetics. Females in this species produce either small eggs that develop into planktonic larvae or large eggs that develop into benthic juveniles. We identify large-effect loci that act maternally to influence larval size and independent, unlinked large-effect loci that act zygotically to affect discrete aspects of larval morphology. The likely fitness of zygotic alleles depends on their maternal background, creating a positive frequency-dependence that may homogenize local populations. Developmental and population genetics interact to shape larval evolution.
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Affiliation(s)
- Christina Zakas
- Center for Genomics & Systems Biology, Department of BiologyNew York UniversityNew YorkUnited States
| | - Jennifer M Deutscher
- Center for Genomics & Systems Biology, Department of BiologyNew York UniversityNew YorkUnited States
| | - Alex D Kay
- Center for Genomics & Systems Biology, Department of BiologyNew York UniversityNew YorkUnited States
| | - Matthew V Rockman
- Center for Genomics & Systems Biology, Department of BiologyNew York UniversityNew YorkUnited States
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Fegaras E, Forer A. Chromosomes selectively detach at one pole and quickly move towards the opposite pole when kinetochore microtubules are depolymerized in Mesostoma ehrenbergii spermatocytes. PROTOPLASMA 2018; 255:1205-1224. [PMID: 29468300 DOI: 10.1007/s00709-018-1214-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Accepted: 01/18/2018] [Indexed: 06/08/2023]
Abstract
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.
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Affiliation(s)
- Eleni Fegaras
- Department of Biology, York University, 4700 Keele St, Toronto, ON, M3J 1P3, Canada
| | - Arthur Forer
- Department of Biology, York University, 4700 Keele St, Toronto, ON, M3J 1P3, Canada.
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Felt KD, Lagerman MB, Ravida NA, Qian L, Powers SR, Paliulis LV. Segregation of the amphitelically attached univalent X chromosome in the spittlebug Philaenus spumarius. PROTOPLASMA 2017; 254:2263-2271. [PMID: 28478487 DOI: 10.1007/s00709-017-1117-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Accepted: 04/25/2017] [Indexed: 06/07/2023]
Abstract
In meiosis I, homologous chromosomes combine to form bivalents, which align on the metaphase plate. Homologous chromosomes then separate in anaphase I. Univalent sex chromosomes, on the other hand, are unable to segregate in the same way as homologous chromosomes of bivalents due to their lack of a homologous pairing partner in meiosis I. Here, we studied univalent segregation in a Hemipteran insect: the spittlebug Philaenus spumarius. We determined the chromosome number and sex determination mechanism in our population of P. spumarius and showed that, in male meiosis I, there is a univalent X chromosome. We discovered that the univalent X chromosome in primary spermatocytes forms an amphitelic attachment to the spindle and aligns on the metaphase plate with the autosomes. Interestingly, the X chromosome remains at spindle midzone long after the autosomes have separated. In late anaphase I, the X chromosome initiates movement towards one spindle pole. This movement appears to be correlated with a loss of microtubule connections between the kinetochore of one chromatid and its associated spindle pole.
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Affiliation(s)
- Kristen D Felt
- Biology Department, Bucknell University, Lewisburg, PA, 17837, USA
| | | | - Nigel A Ravida
- Biology Department, Bucknell University, Lewisburg, PA, 17837, USA
| | - Lu Qian
- Biology Department, Bucknell University, Lewisburg, PA, 17837, USA
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Le TS, Yang FJ, Lo YH, Chang TC, Hsu JC, Kao CY, Wang J. Non-Mendelian assortment of homologous autosomes of different sizes in males is the ancestral state in the Caenorhabditis lineage. Sci Rep 2017; 7:12819. [PMID: 28993668 PMCID: PMC5634442 DOI: 10.1038/s41598-017-13215-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 09/19/2017] [Indexed: 01/25/2023] Open
Abstract
Organismal genome sizes vary by six orders of magnitude and appear positively correlated with organismal size and complexity. Neutral models have been proposed to explain the broad patterns of genome size variation based on organism population sizes. In the Caenorhabditis genus, hermaphrodite genomes are smaller than those of gonochoristic species. One possible driving force for this genome size difference could be non-random chromosome segregation. In Caenorhabditis elegans, chromosome assortment is non-independent and violates Mendel's second law. In males, the shorter homologue of a heterozygous autosome pair preferentially co-segregates with the X chromosome while the longer one preferentially co-segregates with the nullo-X (O) chromosome in a process we call "skew". Since hermaphrodites preferentially receive the shorter chromosomes and can start populations independently, their genome size would be predicted to decrease over evolutionary time. If skew is an important driver for genome size reduction in hermaphroditic Caenorhabditis species, then it should be present in all congeneric species. In this study, we tested this hypothesis and found that skew is present in all eight examined species. Our results suggest that skew is likely the ancestral state in this genus. More speculatively, skew may drive genome size patterns in hermaphroditic species in other nematodes.
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Affiliation(s)
- Tho Son Le
- Biodiversity Research Center, Academia Sinica, Taipei, 11529, Taiwan.,Department of Molecular Genetics and Gene Technology, College of Forestry Biotechnology, Vietnam National University of Forestry, Hanoi, Vietnam
| | - Fang-Jung Yang
- Biodiversity Research Center, Academia Sinica, Taipei, 11529, Taiwan
| | - Yun-Hua Lo
- Biodiversity Research Center, Academia Sinica, Taipei, 11529, Taiwan
| | - Tiffany C Chang
- Biodiversity Research Center, Academia Sinica, Taipei, 11529, Taiwan
| | - Jung-Chen Hsu
- Biodiversity Research Center, Academia Sinica, Taipei, 11529, Taiwan
| | - Chia-Yi Kao
- Biodiversity Research Center, Academia Sinica, Taipei, 11529, Taiwan
| | - John Wang
- Biodiversity Research Center, Academia Sinica, Taipei, 11529, Taiwan.
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Back to the roots: segregation of univalent sex chromosomes in meiosis. Chromosoma 2015; 125:277-86. [PMID: 26511278 DOI: 10.1007/s00412-015-0550-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Revised: 10/06/2015] [Accepted: 10/07/2015] [Indexed: 10/22/2022]
Abstract
In males of many taxa, univalent sex chromosomes normally segregate during the first meiotic division, and analysis of sex chromosome segregation was foundational for the chromosome theory of inheritance. Correct segregation of single or multiple univalent sex chromosomes occurs in a cellular environment where every other chromosome is a bivalent that is being partitioned into homologous chromosomes at anaphase I. The mechanics of univalent chromosome segregation vary among animal taxa. In some, univalents establish syntelic attachment of sister kinetochores to the spindle. In others, amphitelic attachment is established. Here, we review how this problem of segregation of unpaired chromosomes is solved in different animal systems. In addition, we give a short outlook of how mechanistic insights into this process could be gained by explicitly studying model organisms, such as Caenorhabditis elegans.
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