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Chromosome synapsis and recombination in yeast meiosis
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Meiosis is a cell division process that produces haploid gametes from diploid cells. Several important meiotic events take place during prophase of meiosis I, most important being homologous chromosome pairing, meiotic recombination and formation of the synaptonemal complex (SC). These processes assure proper segregation of the homologous chromosomes into the haploid germ cells. Improper segregation of the homologos can cause chromosomal abnormality (aneuploidy), which causes various human disorders, notably mental retardation and pregnancy loss.

This thesis focuses on the relationship between recombination and the formation of SCs, aggregates of SC-related materials (polycomplexes) and recombination enzymes during meiosis. We have investigated SC formation in the absence of recombination, nature of polycomplexes and recombination enzymes in relation to the SCs structures and recombination nodules (RNs) in yeast Saccharomyces cerevisiae.

Studies on yeast mutants suggest that the formation of SCs can take place only in the presence of the initiation of meiotic recombination through the action of the Spo11 enzyme. We have investigated the spo11 mutant of yeast that lacks initiation of meiotic recombination and observed that a fraction of this mutant cells (1.0%) can form complete SCs with wild-type appearance. We have further analyzed a spo11 mutant strain that accumalates at pachytene (spo11∆ndt80∆), and found that the frequency of cells with mature SC formation was 10%. The SC structures were detected in both immuno-fluorescence and electron microscopy (EM). Other phenotypic criteria such as spore viability and homologous chromosome pairing measured by FISH with chromosome specific probes, agrees with several previous reports of the spo11 mutant. Our results suggest that although synapsis is strongly promoted by Spo11 induced DSBs in yeast, it can take place in the absence initiation of meiotic recombination by Spo11 enzyme.

In different organisms, the SCs are found to aggregate as stacks to form polycomplexes (PCs) that commonly occur before or after SC formation. It has generally been believed that the PCs are not attached to the chromosomes. We have investigated the ndt80 mutant of yeast that arrest at pachytene and found that although the SCs in spread chromosome preparations appear as wild type SCs, they appear as PCs in the intact nuclei in EM. In fluorescence in situ hybridization (FISH) with chromosome specific probes, we have shown that the homologous chromosomes in this mutant undergo high level of pairing and are attached to the SCs. In immuno-electron microscopy, two independent anti-DNA antibodies preferentially labeled the lateral element of the PCs. Our data suggests that the SCs in these polycomplexes can be involved in binding of chromosomes and are functional in pairing.

The recombination enzymes, which are involved in the meiotic recombination process are believed to be components of recombination nodules. In some organisms, both early and late recombination enzymes have been shown to be located on RNs, but not in yeast before. We have studied immuno-localization and co-localization of Msh4, Msh5 and Sgs1 recombination enzymes on RNs in pachytene yeast nuclei with a newly developed EM method and found their co-localization on RNs along SCs. Msh4 and Msh5 are found to be located at the edges of RNs on the SCs. We have further analyzed the temporal appearance/disappearance and co-localization pattern of early and late meiotic recombination enzymes in relation to the SC development by immuno-fluorescence. We have been able to detect co-localization between the early meiosis specific enzyme Dmc1 and the late crossing-over related enzymes Msh5 as well as Sgs1. Our data suggest that Msh5 and Sgs1 are recruited to some sites of Dmc1, and thus erases the gap between early and late RNs.

Place, publisher, year, edition, pages
Stockholm: Institutionen för molekylärbiologi och funktionsgenomik , 2004. , 45 p.
Keyword [en]
meiosis, recombination, synapsis, yeast
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:su:diva-225ISBN: 91-7265-929-7 (print)OAI: oai:DiVA.org:su-225DiVA: diva2:191172
Public defence
2004-09-24, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-09-02 Created: 2004-09-02Bibliographically approved
List of papers
1. Meiotic chromosome synapsis in yeast can occur without spo11 induced DNA double strand breaks
Open this publication in new window or tab >>Meiotic chromosome synapsis in yeast can occur without spo11 induced DNA double strand breaks
2004 (English)In: Genetics, ISSN 0016-6731, ISSN 0016-6731, Vol. 168, no 2, 775-783 p.Article in journal (Refereed) Published
Abstract [en]

Proper chromosome segregation and formation of viable gametes depend on synapsis and recombination between homologous chromosomes during meiosis. Previous reports have shown that the synaptic structures, the synaptonemal complexes (SCs), do not occur in yeast cells with the SPO11 gene removed. The Spo11 enzyme makes double-strand breaks (DSBs) in the DNA and thereby initiates recombination. The view has thus developed that synapsis in yeast strictly depends on the initiation of recombination. Synapsis in some other species (Drosophila melanogaster and Caenorhabditis elegans) is independent of recombination events, and SCs are found in spo11 mutants. This difference between species led us to reexamine spo11 deletion mutants of yeast. Using antibodies against Zip1, a SC component, we found that a small fraction (1%) of the spo11 null mutant cells can indeed form wild-type-like SCs. We further looked for synapsis in a spo11 mutant strain that accumulates pachytene cells (spo11Delta ndt80Delta), and found that the frequency of cells with apparently complete SC formation was 10%. Other phenotypic criteria, such as spore viability and homologous chromosome juxtaposition measured by FISH labeling of chromosomal markers, agree with several previous reports of the spo11 mutant. Our results demonstrate that although the Spo11-induced DSBs obviously promote synapsis in yeast, the presence of Spo11 is not an absolute requirement for synapsis.

Place, publisher, year, edition, pages
Genetics, 2004
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-23285 (URN)10.1534/genetics.104.029660 (DOI)
Note
Part of urn:nbn:se:su:diva-225Available from: 2004-09-02 Created: 2004-09-02 Last updated: 2010-01-08Bibliographically approved
2. Lateral elements inside synaptonemal complex-like polycomplexes in ndt80 mutants of yeast bind DNA
Open this publication in new window or tab >>Lateral elements inside synaptonemal complex-like polycomplexes in ndt80 mutants of yeast bind DNA
2003 (English)In: Genetics, ISSN 0016-6731, Vol. 163, no 2, 539-544 p.Article in journal (Refereed) Published
Abstract [en]

The synaptonemal complex (SC) keeps the synapsed homologous chromosomes together during pachytene in meiotic prophase I. Structures that resemble stacks of SCs, polycomplexes, are sometimes found before or after pachytene. We have investigated ndt80 mutants of yeast, which arrest in pachytene. SCs appear normal in spread chromosome preparations, but are only occasionally found in intact nuclei examined in the electron microscope. Instead, large polycomplexes occur in almost every ndt80 mutant nucleus. Immunoelectron microscopy using DNA antibodies show strong preferential labeling to the lateral element parts of the polycomplexes. In situ hybridization using chromosome-specific probes confirms that the chromosomes in ndt80 mutants are paired and attached to the SCs. Our results suggest that polycomplexes can be involved in binding of chromosomes and possibly also in synapsis.

Place, publisher, year, edition, pages
Genetics, 2003
Identifiers
urn:nbn:se:su:diva-23286 (URN)12618393 (PubMedID)
Note
Part of urn:nbn:se:su:diva-225Available from: 2004-09-02 Created: 2004-09-02 Last updated: 2010-01-08Bibliographically approved
3. Temporal linkage between early and late meiotic recombination enzymes in yeast and electron microscope localization of late enzymes in recombination nodules
Open this publication in new window or tab >>Temporal linkage between early and late meiotic recombination enzymes in yeast and electron microscope localization of late enzymes in recombination nodules
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-23287 (URN)
Note
Part of urn:nbn:se:su:diva-225Available from: 2004-09-02 Created: 2004-09-02 Last updated: 2010-01-13Bibliographically approved

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