scholarly journals Heterochromatin Interactions Maintain Homologous Centromere Associations in Mouse Spermatocyte Meiosis

2018 ◽  
Author(s):  
Hoa H. Chuong ◽  
Craig Eyster ◽  
Chih-Ying Lee ◽  
Roberto J. Pezza ◽  
Dean Dawson
Keyword(s):  
Meiotic Prophase ◽  
Meiotic Spindle ◽  
Centromeric Heterochromatin ◽  
Crossing Over ◽  
Homologous Chromosomes ◽  
Meiosis I

SummaryIn meiosis, crossovers between homologous chromosomes link them together. This enables them to attach to microtubules of the meiotic spindle as a unit, such that the homologs will be pulled away from one another at anaphase I. Homologous pairs can sometimes fail to become linked by crossovers. In some organisms, these non-exchange partners are still able segregate properly. In several organisms, associations between the centromeres of non-exchange partners occur in meiotic prophase. These associations have been proposed to promote segregation in meiosis I. But how centromere pairing could promote subsequent proper segregation is unclear. Here we report that meiotic centromere pairing if chromosomes in mouse spermatocytes allows the formation of an association between chromosome pairs. We find that peri-centromeric heterochromatin connections tether the centromeres of chromosome pairs after dissolution of centromere paring. Our results suggest that, in mouse spermatocytes, heterochromatin maintains the association of chromosome centromeres in the absence crossing-over.

scholarly journals Shugoshin protects centromere pairing and promotes segregation of non-exchange partner chromosomes in meiosis

2018 ◽  
Author(s):  
Luciana Previato de Almeida ◽  
Jared M. Evatt ◽  
Hoa H. Chuong ◽  
Emily L. Kurdzo ◽  
Craig A. Eyster ◽  
...  
Keyword(s):  
Synaptonemal Complex ◽  
Chromosome Segregation ◽  
Meiotic Prophase ◽  
Single Unit ◽  
Meiotic Chromosome ◽  
Model Systems ◽  
Meiotic Spindle ◽  
Homologous Chromosomes ◽  
Meiosis I

ABSTRACTFaithful chromosome segregation during meiosis I depends upon the formation of connections between homologous chromosomes. Crossovers between homologs connect the partners allowing them to attach to the meiotic spindle as a unit, such that they migrate away from one another at anaphase I. Homologous partners also become connected by pairing of their centromeres in meiotic prophase. This centromere pairing can promote proper segregation at anaphase I of partners that have failed to become joined by a crossover. Centromere pairing is mediated by synaptonemal complex (SC) proteins that persist at the centromere when the SC disassembles. Here, using mouse spermatocyte and yeast model systems, we tested the role of shugoshin in promoting meiotic centromere pairing by protecting centromeric synaptonemal components from disassembly. The results show that shugoshin protects centromeric SC in meiotic prophase and, in anaphase, promotes the proper segregation of partner chromosomes that are not linked by a crossover.SIGNIFICANCEMeiotic crossovers form a connection between homologous chromosomes that allows them to attach to the spindle as a single unit in meiosis I. In humans, failures in this process are a leading cause of aneuploidy. A recently described process, called centromere pairing, can also help connect meiotic chromosome partners in meiosis. Homologous chromosomes become tightly joined by a structure called the synaptonemal complex (SC) in meiotic prophase. After the SC disassembles, persisting SC proteins at the centromeres mediate their pairing. Here, studies in mouse spermatocytes and yeast are used to show that the shugoshin protein helps SC components persist at centromeres and helps centromere pairing promote the proper segregation of yeast chromosomes that fail to become tethered by crossovers.

scholarly journals Shugoshin protects centromere pairing and promotes segregation of nonexchange partner chromosomes in meiosis

2019 ◽  
Vol 116 (19) ◽  
pp. 9417-9422 ◽  
Author(s):  
Luciana Previato de Almeida ◽  
Jared M. Evatt ◽  
Hoa H. Chuong ◽  
Emily L. Kurdzo ◽  
Craig A. Eyster ◽  
...  
Keyword(s):  
Synaptonemal Complex ◽  
Chromosome Segregation ◽  
Meiotic Prophase ◽  
Model Systems ◽  
Meiotic Spindle ◽  
Homologous Chromosomes ◽  
Meiosis I ◽  
Yeast Model

Faithful chromosome segregation during meiosis I depends upon the formation of connections between homologous chromosomes. Crossovers between homologs connect the partners, allowing them to attach to the meiotic spindle as a unit, such that they migrate away from one another at anaphase I. Homologous partners also become connected by pairing of their centromeres in meiotic prophase. This centromere pairing can promote proper segregation at anaphase I of partners that have failed to become joined by a crossover. Centromere pairing is mediated by synaptonemal complex (SC) proteins that persist at the centromere when the SC disassembles. Here, using mouse spermatocyte and yeast model systems, we tested the role of shugoshin in promoting meiotic centromere pairing by protecting centromeric synaptonemal components from disassembly. The results show that shugoshin protects the centromeric SC in meiotic prophase and, in anaphase, promotes the proper segregation of partner chromosomes that are not linked by a crossover.

Synaptonemal complexes in the mosquito Culex quinquefasciatus

1978 ◽  
Vol 36 (2) ◽  
pp. 212-213
Author(s):  
Annelise Fiil
Keyword(s):  
Nuclear Membrane ◽  
Culex Quinquefasciatus ◽  
Meiotic Prophase ◽  
Crossing Over ◽  
Serial Sections ◽  
Homologous Chromosomes ◽  
Synaptonemal Complexes ◽  
Meiosis I

The presence of synaptonemal complexes between the paired homologous chromosomes at meiotic prophase is a prerequisite for meiotic crossing over, and it may be important for the regular disjunctions of the chromosomes at meiosis I (Moses, 1968; Westergaard and von Wettstein, 1972; Gillies, 1975). Reconstructions of nuclei during zygotene and pachytene have shown that the ends of the synaptonemal complexes in many organisms are attached to the nuclear membrane, often in a polarized fashion (Moens, 1969; Rasmussen, 1976); such a bouquet arrangement of the chromosomes is found in Culex.Materials and MethodsOvaries from Culex quinquefasciatus were fixed in glutaraldehyde, followed by 0s04, and embedded in Epon. The synaptonemal complexes were reconstructed from serial sections.Results and DiscussionCulex has 3 pairs of very long metacentric or slightly submetacentric chromosomes which during pachytene loop around the nucleus several times (Fig. 1). The centromeric regions are fused, and the synaptonemal complexes do not continue through the structure.

scholarly journals Klp2 and Ase1 synergize to maintain meiotic spindle stability during metaphase I

2020 ◽  
Author(s):  
Fan Zheng ◽  
Fenfen Dong ◽  
Shuo Yu ◽  
Tianpeng Li ◽  
Yanze Jian ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Yeast Cells ◽  
Meiotic Spindle ◽  
Homologous Chromosomes ◽  
Spindle Dynamics ◽  
Live Cell Microscopy ◽  
Spindle Stability ◽  
Cell Microscopy ◽  
Mitosis And Meiosis ◽  
Meiosis I

ABSTRACTThe spindle apparatus segregates bi-oriented sister chromatids during mitosis but mono-oriented homologous chromosomes during meiosis I. It has remained unclear if similar molecular mechanisms operate to regulate spindle dynamics during mitosis and meiosis I. Here, we employed live-cell microscopy to compare the spindle dynamics of mitosis and meiosis I in fission yeast cells and demonstrated that the conserved kinesin-14 motor Klp2 plays a specific role in maintaining metaphase spindle length during meiosis I, but not during mitosis. Moreover, the maintenance of metaphase spindle stability during meiosis I requires the synergism between Klp2 and the conserved microtubule crosslinker Ase1 as the absence of both proteins causes exacerbated defects in metaphase spindle stability. The synergism is not necessary for regulating mitotic spindle dynamics. Hence, our work reveals a new molecular mechanism underlying meiotic spindle dynamics and provides insights into understanding differential regulation of meiotic and mitotic events.

scholarly journals Nup132 modulates meiotic spindle attachment in fission yeast by regulating kinetochore assembly

2015 ◽  
Vol 211 (2) ◽  
pp. 295-308 ◽  
Author(s):  
Hui-Ju Yang ◽  
Haruhiko Asakawa ◽  
Tokuko Haraguchi ◽  
Yasushi Hiraoka
Keyword(s):  
Schizosaccharomyces Pombe ◽  
Fission Yeast ◽  
Meiotic Prophase ◽  
Spindle Assembly Checkpoint ◽  
Meiotic Spindle ◽  
Spindle Attachment ◽  
Kinetochore Assembly ◽  
Sister Chromatids ◽  
Monopolar Spindle ◽  
Meiosis I

During meiosis, the kinetochore undergoes substantial reorganization to establish monopolar spindle attachment. In the fission yeast Schizosaccharomyces pombe, the KNL1–Spc7-Mis12-Nuf2 (KMN) complex, which constitutes the outer kinetochore, is disassembled during meiotic prophase and is reassembled before meiosis I. Here, we show that the nucleoporin Nup132 is required for timely assembly of the KMN proteins: In the absence of Nup132, Mis12 and Spc7 are precociously assembled at the centromeres during meiotic prophase. In contrast, Nuf2 shows timely dissociation and reappearance at the meiotic centromeres. We further demonstrate that depletion of Nup132 activates the spindle assembly checkpoint in meiosis I, possibly because of the increased incidence of erroneous spindle attachment at sister chromatids. These results suggest that precocious assembly of the kinetochores leads to the meiosis I defects observed in the nup132-disrupted mutant. Thus, we propose that Nup132 plays an important role in establishing monopolar spindle attachment at meiosis I through outer kinetochore reorganization at meiotic prophase.

scholarly journals Telomeres and centromeres have interchangeable roles in promoting meiotic spindle formation

2015 ◽  
Vol 208 (4) ◽  
pp. 415-428 ◽  
Author(s):  
Alex Fennell ◽  
Alfonso Fernández-Álvarez ◽  
Kazunori Tomita ◽  
Julia Promisel Cooper
Keyword(s):  
Fission Yeast ◽  
Nuclear Membrane ◽  
Meiotic Prophase ◽  
Meiotic Spindle ◽  
The Sun ◽  
Spindle Formation ◽  
Domain Protein ◽  
Bipolar Spindles ◽  
Sun Domain ◽  
Meiosis I

Telomeres and centromeres have traditionally been considered to perform distinct roles. During meiotic prophase, in a conserved chromosomal configuration called the bouquet, telomeres gather to the nuclear membrane (NM), often near centrosomes. We found previously that upon disruption of the fission yeast bouquet, centrosomes failed to insert into the NM at meiosis I and nucleate bipolar spindles. Hence, the trans-NM association of telomeres with centrosomes during prophase is crucial for efficient spindle formation. Nonetheless, in approximately half of bouquet-deficient meiocytes, spindles form properly. Here, we show that bouquet-deficient cells can successfully undergo meiosis using centromere–centrosome contact instead of telomere–centrosome contact to generate spindle formation. Accordingly, forced association between centromeres and centrosomes fully rescued the spindle defects incurred by bouquet disruption. Telomeres and centromeres both stimulate focal accumulation of the SUN domain protein Sad1 beneath the centrosome, suggesting a molecular underpinning for their shared spindle-generating ability. Our observations demonstrate an unanticipated level of interchangeability between the two most prominent chromosomal landmarks.

Using a Model to Teach Crossing Over

2017 ◽  
Vol 79 (4) ◽  
pp. 305-308
Author(s):  
Feride Keskin ◽  
Aylin Çam
Keyword(s):  
Cell Division ◽  
Crossing Over ◽  
Homologous Chromosomes ◽  
Meiosis I

The purpose of this activity is to model the formation of homologous chromosomes and the crossing over realized in meiosis I cell division. The model established through the activities conducted will allow students to visualize homologous chromosomes and the formation of crossing over among them. The model will help students to understand how homologous chromosomes occur and how crossing over is realized between homologous chromosomes whose chromatids are not sisters. The developed model is found to be an effective tool in teaching crossing over.

Meiosis in a temperature-sensitive DNA-synthesis mutant and in an apomictic yeast strain ( Saccharomyces cerevisiae )

1977 ◽  
Vol 277 (955) ◽  
pp. 351-358 ◽  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Dna Synthesis ◽  
Meiotic Prophase ◽  
Yeast Strain ◽  
Meiotic Spindle ◽  
Temperature Sensitive ◽  
Restrictive Temperature ◽  
Yeast Mutant ◽  
Synaptonemal Complexes ◽  
Meiosis I

It is shown that in the temperature-sensitive yeast mutant ( Saccharomyces cerevisiae ) spo 11 at the restrictive temperature of 34 °C, (1) premeiotic DNA synthesis is nearly completely blocked; (2) the nucleus enters meiotic prophase indicated by the formation of axial cores and polysynaptonemal complexes; (3) the kinetic apparatus functions normally at meiosis I and II; (4) early spore formation occurs in nearly all cells but it is variable and all spores eventually degenerate. It is concluded that chromosome replication is not a prerequisite for the functions listed above. The apomictic yeast strain 4117 produces 2 diploid spores. It is shown that a diploid which produces 2-spored asci, synthesized from 4117, no. 5, and an adenine requiring strain (1) has a normal meiotic prophase with abundant synaptonemal complexes; (2) has only one meiotic spindle; (3) has spores which form red clones more frequently than normal or u.v.-treated vegetative cells form ade/ade red sectors through mitotic recombination. It is concluded that this apomictic yeast has main­tained meiotic prophase, but that one of the two meiotic divisions is suppressed.

scholarly journals Klp2 and Ase1 synergize to maintain meiotic spindle stability during metaphase I

2020 ◽  
Vol 295 (38) ◽  
pp. 13287-13298
Author(s):  
Fan Zheng ◽  
Fenfen Dong ◽  
Shuo Yu ◽  
Tianpeng Li ◽  
Yanze Jian ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Yeast Cells ◽  
Meiotic Spindle ◽  
Homologous Chromosomes ◽  
Spindle Dynamics ◽  
Live Cell Microscopy ◽  
Spindle Stability ◽  
Cell Microscopy ◽  
Mitosis And Meiosis ◽  
Meiosis I

The spindle apparatus segregates bi-oriented sister chromatids during mitosis but mono-oriented homologous chromosomes during meiosis I. It has remained unclear if similar molecular mechanisms operate to regulate spindle dynamics during mitosis and meiosis I. Here, we employed live-cell microscopy to compare the spindle dynamics of mitosis and meiosis I in fission yeast cells and demonstrated that the conserved kinesin-14 motor Klp2 plays a specific role in maintaining metaphase spindle length during meiosis I but not during mitosis. Moreover, the maintenance of metaphase spindle stability during meiosis I requires the synergism between Klp2 and the conserved microtubule cross-linker Ase1, as the absence of both proteins causes exacerbated defects in metaphase spindle stability. The synergism is not necessary for regulating mitotic spindle dynamics. Hence, our work reveals a new molecular mechanism underlying meiotic spindle dynamics and provides insights into understanding differential regulation of meiotic and mitotic events.

Effects of Homology, Size and Exchange on the Meiotic Segregation of Model Chromosomes in Saccharomyces cerevisiae

Genetics ◽  
1996 ◽  
Vol 142 (1) ◽  
pp. 79-89 ◽  
Author(s):  
Lyle O Ross ◽  
Susannah Rankin ◽  
Michèle F Shuster ◽  
Dean S Dawson
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Dna Sequences ◽  
Crossing Over ◽  
Chromosome Size ◽  
Meiotic Segregation ◽  
Yeast Saccharomyces Cerevisiae ◽  
Homologous Chromosomes ◽  
Reciprocal Recombination ◽  
Eukaryotic Organisms ◽  
Meiosis I

In most eukaryotic organisms, chiasmata, the connections formed between homologous chromosomes as a consequence of crossing over, are important for ensuring that the homologues move away from each other at meiosis I. Some organisms have the capacity to partition the rare homologues that have failed to experience reciprocal recombination. The yeast Saccharomyces cerevisiae is able to correctly partition achiasmate homologues with low fidelity by a mechanism that is largely unknown. It is possible to test which parameters affect the ability of achiasmate chromosomes to segregate by constructing strains that will have three achiasmate chromosomes at the time of meiosis. The meiotic partitioning of these chromosomes can be monitored to determine which ones segregate away from each other at meiosis I. This approach was used to test the influence of homologous yeast DNA sequences, recombination intiation sites, chromosome size and crossing over on the meiotic segregation of the model chromosomes. Chrome some size had no effect on achiasmate segregation. The influence of homologous yeast sequences on the segregation of noncrossover model chromosomes was negligible. In meioses in which two of the three model chromosomes experienced a crossover, they nearly always disjoined at meiosis I.

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