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1.
Nat Commun ; 12(1): 4674, 2021 08 03.
Artigo em Inglês | MEDLINE | ID: mdl-34344879

RESUMO

In most organisms, the number and distribution of crossovers that occur during meiosis are tightly controlled. All chromosomes must receive at least one 'obligatory crossover' and crossovers are prevented from occurring near one another by 'crossover interference'. However, the mechanistic basis of this phenomenon of crossover interference has remained mostly mysterious. Using quantitative super-resolution cytogenetics and mathematical modelling, we investigate crossover positioning in the Arabidopsis thaliana wild-type, an over-expressor of the conserved E3 ligase HEI10, and a hei10 heterozygous line. We show that crossover positions can be explained by a predictive, diffusion-mediated coarsening model, in which large, approximately evenly-spaced HEI10 foci grow at the expense of smaller, closely-spaced clusters. We propose this coarsening process explains many aspects of Arabidopsis crossover positioning, including crossover interference. Consistent with this model, we also demonstrate that crossover positioning can be predictably modified in vivo simply by altering HEI10 dosage, with higher and lower dosage leading to weaker and stronger crossover interference, respectively. As HEI10 is a conserved member of the RING finger protein family that functions in the interference-sensitive pathway for crossover formation, we anticipate that similar mechanisms may regulate crossover positioning in diverse eukaryotes.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Proteínas Cromossômicas não Histona/metabolismo , Troca Genética/genética , Meiose/genética , Proteínas de Arabidopsis/genética , Proteínas Cromossômicas não Histona/genética , Cromossomos de Plantas/genética , Cromossomos de Plantas/metabolismo , Simulação por Computador , Dosagem de Genes , Estágio Paquíteno/genética , Complexo Sinaptonêmico/genética , Complexo Sinaptonêmico/metabolismo
2.
Nat Struct Mol Biol ; 28(8): 681-693, 2021 08.
Artigo em Inglês | MEDLINE | ID: mdl-34373646

RESUMO

The synaptonemal complex (SC) is a supramolecular protein assembly that mediates synapsis between homologous chromosomes during meiosis. SC elongation along the chromosome length (up to 24 µm) depends on its midline α-fibrous component SYCE2-TEX12. Here, we report X-ray crystal structures of human SYCE2-TEX12 as an individual building block and on assembly within a fibrous lattice. We combine these structures with mutagenesis, biophysics and electron microscopy to reveal the hierarchical mechanism of SYCE2-TEX12 fiber assembly. SYCE2-TEX12's building blocks are 2:2 coiled coils that dimerize into 4:4 hetero-oligomers and interact end-to-end and laterally to form 10-nm fibers that intertwine within 40-nm bundled micrometer-long fibers that define the SC's midline structure. This assembly mechanism bears striking resemblance with intermediate filament proteins vimentin, lamin and keratin. Thus, SYCE2-TEX12 exhibits behavior typical of cytoskeletal proteins to provide an α-fibrous SC backbone that structurally underpins synaptic elongation along meiotic chromosomes.


Assuntos
Proteínas de Ciclo Celular/metabolismo , Pareamento Cromossômico/fisiologia , Complexo Sinaptonêmico/metabolismo , Cristalografia por Raios X , Proteínas do Citoesqueleto/metabolismo , Humanos , Queratinas/metabolismo , Laminas/metabolismo , Meiose/fisiologia , Estrutura Quaternária de Proteína , Vimentina/metabolismo
3.
Nucleic Acids Res ; 49(13): 7537-7553, 2021 07 21.
Artigo em Inglês | MEDLINE | ID: mdl-34197600

RESUMO

The synaptonemal complex (SC) is a proteinaceous structure that mediates homolog engagement and genetic recombination during meiosis. In budding yeast, Zip-Mer-Msh (ZMM) proteins promote crossover (CO) formation and initiate SC formation. During SC elongation, the SUMOylated SC component Ecm11 and the Ecm11-interacting protein Gmc2 facilitate the polymerization of Zip1, an SC central region component. Through physical recombination, cytological, and genetic analyses, we found that ecm11 and gmc2 mutants exhibit chromosome-specific defects in meiotic recombination. CO frequencies on a short chromosome (chromosome III) were reduced, whereas CO and non-crossover frequencies on a long chromosome (chromosome VII) were elevated. Further, in ecm11 and gmc2 mutants, more double-strand breaks (DSBs) were formed on a long chromosome during late prophase I, implying that the Ecm11-Gmc2 (EG) complex is involved in the homeostatic regulation of DSB formation. The EG complex may participate in joint molecule (JM) processing and/or double-Holliday junction resolution for ZMM-dependent CO-designated recombination. Absence of the EG complex ameliorated the JM-processing defect in zmm mutants, suggesting a role for the EG complex in suppressing ZMM-independent recombination. Our results suggest that the SC central region functions as a compartment for sequestering recombination-associated proteins to regulate meiosis specificity during recombination.


Assuntos
Proteínas de Ciclo Celular/genética , Troca Genética , Quebras de DNA de Cadeia Dupla , Meiose/genética , Proteínas de Saccharomyces cerevisiae/genética , Complexo Sinaptonêmico/metabolismo , Cromossomos Fúngicos , Replicação do DNA , Proteínas de Ligação a DNA/genética , Endonucleases/genética , Retroalimentação Fisiológica , Deleção de Genes , Recombinação Genética , Saccharomyces cerevisiae/genética , Temperatura , Fatores de Transcrição/genética , Ubiquitina-Proteína Ligases/genética
4.
Philos Trans A Math Phys Eng Sci ; 379(2199): 20200144, 2021 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-33896204

RESUMO

We report that high-density single-molecule super-resolution microscopy can be achieved with a conventional epifluorescence microscope set-up and a mercury arc lamp. The configuration termed as laser-free super-resolution microscopy (LFSM) is an extension of single-molecule localization microscopy (SMLM) techniques and allows single molecules to be switched on and off (a phenomenon termed as 'blinking'), detected and localized. The use of a short burst of deep blue excitation (350-380 nm) can be further used to reactivate the blinking, once the blinking process has slowed or stopped. A resolution of 90 nm is achieved on test specimens (mouse and amphibian meiotic chromosomes). Finally, we demonstrate that stimulated emission depletion and LFSM can be performed on the same biological sample using a simple commercial mounting medium. It is hoped that this type of correlative imaging will provide a basis for a further enhanced resolution. This article is part of the Theo Murphy meeting issue 'Super-resolution structured illumination microscopy (part 1)'.


Assuntos
Microscopia de Fluorescência/instrumentação , Imagem Individual de Molécula/instrumentação , Anfíbios , Animais , Cromossomos/química , Cromossomos/ultraestrutura , Desenho de Equipamento , Corantes Fluorescentes , Camundongos , Microscopia Confocal/instrumentação , Microscopia Confocal/métodos , Microscopia de Fluorescência/métodos , Compostos Orgânicos , Estudo de Prova de Conceito , Imagem Individual de Molécula/métodos , Complexo Sinaptonêmico/química , Complexo Sinaptonêmico/ultraestrutura , Xantenos
5.
Proc Natl Acad Sci U S A ; 118(12)2021 03 23.
Artigo em Inglês | MEDLINE | ID: mdl-33723072

RESUMO

Meiotic crossovers (COs) have intriguing patterning properties, including CO interference, the tendency of COs to be well-spaced along chromosomes, and heterochiasmy, the marked difference in male and female CO rates. During meiosis, transverse filaments transiently associate the axes of homologous chromosomes, a process called synapsis that is essential for CO formation in many eukaryotes. Here, we describe the spatial organization of the transverse filaments in Arabidopsis (ZYP1) and show it to be evolutionary conserved. We show that in the absence of ZYP1 (zyp1a zyp1b null mutants), chromosomes associate in pairs but do not synapse. Unexpectedly, in absence of ZYP1, CO formation is not prevented but increased. Furthermore, genome-wide analysis of recombination revealed that CO interference is abolished, with the frequent observation of close COs. In addition, heterochiasmy was erased, with identical CO rates in males and females. This shows that the tripartite synaptonemal complex is dispensable for CO formation and has a key role in regulating their number and distribution, imposing CO interference and heterochiasmy.


Assuntos
Arabidopsis/fisiologia , Troca Genética , Complexo Sinaptonêmico/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Biomarcadores , Sistemas CRISPR-Cas , Cromossomos de Plantas , Edição de Genes , Meiose/genética , Mutagênese
6.
Curr Genet ; 67(4): 553-565, 2021 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-33712914

RESUMO

The generally conserved AAA+ ATPase Pch2/TRIP13 is involved in diverse aspects of meiosis, such as prophase checkpoint function, DNA break regulation, and meiotic recombination. The controlled recruitment of Pch2 to meiotic chromosomes allows it to use its ATPase activity to influence HORMA protein-dependent signaling. Because of the connection between Pch2 chromosomal recruitment and its functional roles in meiosis, it is important to reveal the molecular details that govern Pch2 localization. Here, we review the current understanding of the different factors that control the recruitment of Pch2 to meiotic chromosomes, with a focus on research performed in budding yeast. During meiosis in this organism, Pch2 is enriched within the nucleolus, where it likely associates with the specialized chromatin of the ribosomal (r)DNA. Pch2 is also found on non-rDNA euchromatin, where its recruitment is contingent on Zip1, a component of the synaptonemal complex (SC) that assembles between homologous chromosomes. We discuss recent findings connecting the recruitment of Pch2 with its association with the Origin Recognition Complex (ORC) and reliance on RNA Polymerase II-dependent transcription. In total, we provide a comprehensive overview of the pathways that control the chromosomal association of an important meiotic regulator.


Assuntos
ATPases Associadas a Diversas Atividades Celulares/genética , Meiose/genética , Proteínas Nucleares/genética , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Ciclo Celular/genética , Cromossomos/genética , Complexo de Reconhecimento de Origem/genética , Saccharomyces cerevisiae/genética , Complexo Sinaptonêmico/genética
7.
Plant Cell ; 33(5): 1633-1656, 2021 07 02.
Artigo em Inglês | MEDLINE | ID: mdl-33659989

RESUMO

Meiosis is a specialized cell division that gives rise to genetically distinct gametic cells. Meiosis relies on the tightly controlled formation of DNA double-strand breaks (DSBs) and their repair via homologous recombination for correct chromosome segregation. Like all forms of DNA damage, meiotic DSBs are potentially harmful and their formation activates an elaborate response to inhibit excessive DNA break formation and ensure successful repair. Previous studies established the protein kinase ATM as a DSB sensor and meiotic regulator in several organisms. Here we show that Arabidopsis ATM acts at multiple steps during DSB formation and processing, as well as crossover (CO) formation and synaptonemal complex (SC) organization, all vital for the successful completion of meiosis. We developed a single-molecule approach to quantify meiotic breaks and determined that ATM is essential to limit the number of meiotic DSBs. Local and genome-wide recombination screens showed that ATM restricts the number of interference-insensitive COs, while super-resolution STED nanoscopy of meiotic chromosomes revealed that the kinase affects chromatin loop size and SC length and width. Our study extends our understanding of how ATM functions during plant meiosis and establishes it as an integral factor of the meiotic program.


Assuntos
Arabidopsis/metabolismo , Quebras de DNA de Cadeia Dupla , Meiose , Recombinação Genética/genética , Complexo Sinaptonêmico/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Proteínas Mutadas de Ataxia Telangiectasia/genética , Proteínas Mutadas de Ataxia Telangiectasia/metabolismo , Cromatina/metabolismo , Troca Genética , Reparo do DNA , Fertilidade , Mutação/genética , Recombinases/metabolismo
8.
Genetics ; 217(1): 1-11, 2021 03 03.
Artigo em Inglês | MEDLINE | ID: mdl-33683358

RESUMO

In most species that reproduce sexually, successful gametogenesis requires recombination during meiosis. The number and placement of crossovers (COs) vary among individuals, with females and males often presenting the most striking contrasts. Despite the recognition that the sexes recombine at different rates (heterochiasmy), existing data fail to answer the question of whether patterns of genetic variation in recombination rate are similar in the two sexes. To fill this gap, we measured the genome-wide recombination rate in both sexes from a panel of wild-derived inbred strains from multiple subspecies of house mice (Mus musculus) and from a few additional species of Mus. To directly compare recombination rates in females and males from the same genetic backgrounds, we applied established methods based on immunolocalization of recombination proteins to inbred strains. Our results reveal discordant patterns of genetic variation in the two sexes. Whereas male genome-wide recombination rates vary substantially among strains, female recombination rates measured in the same strains are more static. The direction of heterochiasmy varies within two subspecies, Mus musculus molossinus and Mus musculus musculus. The direction of sex differences in the length of the synaptonemal complex and CO positions is consistent across strains and does not track sex differences in genome-wide recombination rate. In males, contrasts between strains with high recombination rate and strains with low recombination rate suggest more recombination is associated with stronger CO interference and more double-strand breaks. The sex-specific patterns of genetic variation we report underscore the importance of incorporating sex differences into recombination research.


Assuntos
Troca Genética , Variação Genética , Animais , Feminino , Patrimônio Genético , Genoma , Masculino , Camundongos , Fatores Sexuais , Especificidade da Espécie , Complexo Sinaptonêmico/metabolismo
9.
Int J Mol Sci ; 22(5)2021 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-33673731

RESUMO

During meiosis, the number of crossovers vary in correlation to the length of prophase chromosome axes at the synaptonemal complex stage. It has been proposed that the regular spacing of the DNA loops, along with the close relationship of the recombination complexes and the meiotic axes are at the basis of this covariation. Here, we use a cytogenomic approach to investigate the relationship between the synaptonemal complex length and the DNA content in chicken oocytes during the pachytene stage of the first meiotic prophase. The synaptonemal complex to DNA ratios of specific chromosomes and chromosome segments were compared against the recombination rates obtained by MLH1 focus mapping. The present results show variations in the DNA packing ratios of macro- and microbivalents and also between regions within the same bivalent. Chromosome or chromosome regions with higher crossover rates form comparatively longer synaptonemal complexes than expected based on their DNA content. These observations are compatible with the formation of higher number of shorter DNA loops along meiotic axes in regions with higher recombination levels.


Assuntos
Cromossomos de Mamíferos/genética , Troca Genética , DNA/genética , Meiose , Oócitos/metabolismo , Recombinação Genética , Complexo Sinaptonêmico , Animais , Galinhas , DNA/química , Feminino , Proteína 1 Homóloga a MutL/metabolismo , Oócitos/citologia
10.
PLoS Genet ; 17(3): e1009205, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-33730019

RESUMO

During sexual reproduction the parental homologous chromosomes find each other (pair) and align along their lengths by integrating local sequence homology with large-scale contiguity, thereby allowing for precise exchange of genetic information. The Synaptonemal Complex (SC) is a conserved zipper-like structure that assembles between the homologous chromosomes, bringing them together and regulating exchanges between them. However, the molecular mechanisms by which the SC carries out these functions remain poorly understood. Here we isolated and characterized two mutations in the dimerization interface in the middle of the SC zipper in C. elegans. The mutations perturb both chromosome alignment and the regulation of genetic exchanges. Underlying the chromosome-scale phenotypes are distinct alterations to the way SC subunits interact with one another. We propose a model whereby the SC brings homologous chromosomes together through two activities: obligate zipping that prevents assembly on unpaired chromosomes; and a tendency to extend pairing interactions along the entire length of the chromosomes.


Assuntos
Pareamento Cromossômico , Troca Genética , Meiose/genética , Complexo Sinaptonêmico , Sequência de Aminoácidos , Animais , Proteínas de Caenorhabditis elegans/química , Proteínas de Caenorhabditis elegans/metabolismo , Imunofluorescência , Imuno-Histoquímica , Masculino , Mutação , Proteínas Nucleares/química , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Ligação Proteica , Domínios e Motivos de Interação entre Proteínas , Complexo Sinaptonêmico/metabolismo , Complexo Sinaptonêmico/ultraestrutura
11.
Am J Hum Genet ; 108(2): 324-336, 2021 02 04.
Artigo em Inglês | MEDLINE | ID: mdl-33508233

RESUMO

Human infertility is a multifactorial disease that affects 8%-12% of reproductive-aged couples worldwide. However, the genetic causes of human infertility are still poorly understood. Synaptonemal complex (SC) is a conserved tripartite structure that holds homologous chromosomes together and plays an indispensable role in the meiotic progression. Here, we identified three homozygous mutations in the SC coding gene C14orf39/SIX6OS1 in infertile individuals from different ethnic populations by whole-exome sequencing (WES). These mutations include a frameshift mutation (c.204_205del [p.His68Glnfs∗2]) from a consanguineous Pakistani family with two males suffering from non-obstructive azoospermia (NOA) and one female diagnosed with premature ovarian insufficiency (POI) as well as a nonsense mutation (c.958G>T [p.Glu320∗]) and a splicing mutation (c.1180-3C>G) in two unrelated Chinese men (individual P3907 and individual P6032, respectively) with meiotic arrest. Mutations in C14orf39 resulted in truncated proteins that retained SYCE1 binding but exhibited impaired polycomplex formation between C14ORF39 and SYCE1. Further cytological analyses of meiosis in germ cells revealed that the affected familial males with the C14orf39 frameshift mutation displayed complete asynapsis between homologous chromosomes, while the affected Chinese men carrying the nonsense or splicing mutation showed incomplete synapsis. The phenotypes of NOA and POI in affected individuals were well recapitulated by Six6os1 mutant mice carrying an analogous mutation. Collectively, our findings in humans and mice highlight the conserved role of C14ORF39/SIX6OS1 in SC assembly and indicate that the homozygous mutations in C14orf39/SIX6OS1 described here are responsible for infertility of these affected individuals, thus expanding our understanding of the genetic basis of human infertility.


Assuntos
Azoospermia/genética , Mutação , Insuficiência Ovariana Primária/genética , Adulto , Azoospermia/fisiopatologia , Pareamento Cromossômico , Códon sem Sentido , Proteínas de Ligação a DNA/metabolismo , Feminino , Homozigoto , Humanos , Masculino , Meiose , Pessoa de Meia-Idade , Proteínas Nucleares/metabolismo , Linhagem , Insuficiência Ovariana Primária/fisiopatologia , Espermatócitos/metabolismo , Espermatócitos/fisiologia , Complexo Sinaptonêmico/genética , Complexo Sinaptonêmico/metabolismo , Sequenciamento Completo do Genoma
12.
Exp Cell Res ; 399(2): 112455, 2021 02 15.
Artigo em Inglês | MEDLINE | ID: mdl-33400935

RESUMO

During meiosis, homologous chromosomes exchange genetic material. This exchange or meiotic recombination is mediated by a proteinaceous scaffold known as the Synaptonemal complex (SC). Any defects in its formation produce failures in meiotic recombination, chromosome segregation and meiosis completion. It has been proposed that DNA repair events that will be resolved by crossover between homologous chromosomes are predetermined by the SC. Hence, structural analysis of the organization of the DNA in the SC could shed light on the process of crossover interference. In this work, we employed an ultrastructural DNA staining technique on mouse testis and followed nuclei of pachytene cells. We observed structures organized similarly to the SCs stained with conventional techniques. These structures, presumably the DNA in the SCs, are delineating the edges of both lateral elements and no staining was observed between them. DNA in the LEs resembles two parallel tracks. However, a bubble-like staining pattern in certain regions of the SC was observed. Furthermore, this staining pattern is found in SCs formed between non-homologous chromosomes, in SCs formed between sister chromatids and in SCs without lateral elements, suggesting that this particular organization of the DNA is determined by the synapsis of the chromosomes despite their lack of homology or the presence of partially formed SCs.


Assuntos
Proteínas de Ligação a DNA/metabolismo , DNA/metabolismo , Meiose/fisiologia , Complexo Sinaptonêmico/metabolismo , Animais , Proteínas de Ciclo Celular/química , Proteínas de Ciclo Celular/metabolismo , Cromátides/química , Cromátides/metabolismo , Cromátides/ultraestrutura , Pareamento Cromossômico/fisiologia , DNA/química , DNA/ultraestrutura , Substâncias Macromoleculares/química , Substâncias Macromoleculares/metabolismo , Masculino , Camundongos , Camundongos Knockout , Proteínas Nucleares/química , Proteínas Nucleares/metabolismo , Conformação de Ácido Nucleico , Estrutura Quaternária de Proteína , Complexo Sinaptonêmico/fisiologia , Complexo Sinaptonêmico/ultraestrutura
13.
J Exp Bot ; 72(8): 3012-3027, 2021 04 02.
Artigo em Inglês | MEDLINE | ID: mdl-33502451

RESUMO

Meiosis generates genetic variation through homologous recombination (HR) that is harnessed during breeding. HR occurs in the context of meiotic chromosome axes and the synaptonemal complex. To study the role of axis remodelling in crossover (CO) formation in a crop species, we characterized mutants of the axis-associated protein ASY1 and the axis-remodelling protein PCH2 in Brassica rapa. asy1 plants form meiotic chromosome axes that fail to synapse. CO formation is almost abolished, and residual chiasmata are proportionally enriched in terminal chromosome regions, particularly in the nucleolar organizing region (NOR)-carrying chromosome arm. pch2 plants show impaired ASY1 loading and remodelling, consequently achieving only partial synapsis, which leads to reduced CO formation and loss of the obligatory CO. PCH2-independent chiasmata are proportionally enriched towards distal chromosome regions. Similarly, in Arabidopsis pch2, COs are increased towards telomeric regions at the expense of (peri-) centromeric COs compared with the wild type. Taken together, in B. rapa, axis formation and remodelling are critical for meiotic fidelity including synapsis and CO formation, and in asy1 and pch2 CO distributions are altered. While asy1 plants are sterile, pch2 plants are semi-sterile and thus PCH2 could be an interesting target for breeding programmes.


Assuntos
Brassica rapa , Recombinação Homóloga , Meiose , Brassica rapa/genética , Pareamento Cromossômico , Proteínas de Ligação a DNA/genética , Meiose/genética , Melhoramento Vegetal , Complexo Sinaptonêmico/genética
14.
Life Sci Alliance ; 4(2)2021 02.
Artigo em Inglês | MEDLINE | ID: mdl-33293336

RESUMO

Homologous chromosomes pair with each other during meiosis, culminating in the formation of the synaptonemal complex (SC), which is coupled with meiotic recombination. In this study, we showed that a meiosis-specific depletion mutant of a cullin (Cdc53) in the SCF (Skp-Cullin-F-box) ubiquitin ligase, which plays a critical role in cell cycle regulation during mitosis, is deficient in SC formation. However, the mutant is proficient in forming crossovers, indicating the uncoupling of meiotic recombination with SC formation in the mutant. Furthermore, the deletion of the PCH2 gene encoding a meiosis-specific AAA+ ATPase suppresses SC-assembly defects induced by CDC53 depletion. On the other hand, the pch2 cdc53 double mutant is defective in meiotic crossover formation, suggesting the assembly of SC with unrepaired DNA double-strand breaks. A temperature-sensitive mutant of CDC4, which encodes an F-box protein of SCF, shows meiotic defects similar to those of the CDC53-depletion mutant. These results suggest that SCFCdc4, probably SCFCdc4-dependent protein ubiquitylation, regulates and collaborates with Pch2 in SC assembly and meiotic recombination.


Assuntos
Proteínas de Ciclo Celular/metabolismo , Proteínas F-Box/metabolismo , Meiose/fisiologia , Proteínas de Saccharomyces cerevisiae/metabolismo , Complexo Sinaptonêmico/metabolismo , Ubiquitina-Proteína Ligases/metabolismo , Pontos de Checagem do Ciclo Celular/genética , Proteínas de Ciclo Celular/genética , Proteínas Culina/genética , Proteínas Culina/metabolismo , Proteínas F-Box/genética , Deleção de Genes , Mutação , Recombinação Genética , Proteínas de Saccharomyces cerevisiae/genética , Ubiquitina-Proteína Ligases/genética
15.
J Cell Biol ; 220(2)2021 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-33382409

RESUMO

Meiosis creates genetic diversity by recombination and segregation of chromosomes. The synaptonemal complex assembles during meiotic prophase I and assists faithful exchanges between homologous chromosomes, but how its assembly/disassembly is regulated remains to be understood. Here, we report how two major posttranslational modifications, phosphorylation and ubiquitination, cooperate to promote synaptonemal complex assembly. We found that the ubiquitin ligase complex SCF is important for assembly and maintenance of the synaptonemal complex in Drosophila female meiosis. This function of SCF is mediated by two substrate-recognizing F-box proteins, Slmb/ßTrcp and Fbxo42. SCF-Fbxo42 down-regulates the phosphatase subunit PP2A-B56, which is important for synaptonemal complex assembly and maintenance.


Assuntos
Regulação para Baixo , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Proteínas F-Box/metabolismo , Proteína Fosfatase 2/metabolismo , Proteínas Ligases SKP Culina F-Box/metabolismo , Complexo Sinaptonêmico/metabolismo , Animais , Quebras de DNA de Cadeia Dupla , Meiose , Recombinação Genética/genética
16.
Cancer Sci ; 112(3): 989-996, 2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33382503

RESUMO

The synaptonemal complex (SC) is a proteinaceous structure that is transiently formed during meiosis to promote homologous recombination between maternal and paternal chromosomes. As this structure is required only for meiotic recombination, the proteins constituting the complex are almost undetectable in normal somatic cells, but they can be expressed under the conditions in which the transcriptional machinery is deregulated. Accumulating evidence indicates that they are epigenetically expressed in cancers of various origin. Not surprisingly, in contrast to their meiotic roles, the somatic roles of the SC proteins remain to be investigated. However, it has recently been reported that SYCP3 and SYCE2 control DNA double-strand break repair negatively and positively, respectively, suggesting that the ectopic expression of the SC proteins in somatic cells could be associated with the maintenance of genomic instability. Thus, it is highly likely that the investigation of the somatic roles of the SC proteins would improve our understanding of the mechanisms underlying tumor development.


Assuntos
Epigênese Genética , Instabilidade Genômica , Neoplasias/genética , Complexo Sinaptonêmico/metabolismo , Animais , Proteínas de Ciclo Celular/metabolismo , Quebras de DNA de Cadeia Dupla , Proteínas de Ligação a DNA/metabolismo , Humanos , Camundongos , Modelos Animais , Proteínas Nucleares/metabolismo , Reparo de DNA por Recombinação
17.
Genes Dev ; 34(23-24): 1562-1564, 2020 12 01.
Artigo em Inglês | MEDLINE | ID: mdl-33262143

RESUMO

Proper segregation during meiosis requires that homologs be connected by the combination of crossovers and sister chromatid cohesion. To generate crossovers, numerous double-strand breaks (DSBs) are introduced throughout the genome by the conserved Spo11 endonuclease. DSB formation and its repair are then highly regulated to ensure that homologous chromosomes contain at least one crossover and no DSBs remain prior to meiosis I segregation. The synaptonemal complex (SC) is a meiosis-specific structure formed between homologous chromosomes during prophase that promotes DSB formation and biases repair of DSBs to homologs over sister chromatids. Synapsis occurs when a particular recombination pathway is successful in establishing stable interhomolog connections. In this issue of Genes & Development, Mu and colleagues (pp. 1605-1618) show that SC formation between individual chromosomes provides the feedback to down-regulate Spo11 activity, thereby revealing an additional function for the SC.


Assuntos
Quebras de DNA de Cadeia Dupla , Complexo Sinaptonêmico , Cromátides , Recombinação Homóloga , Meiose
18.
PLoS Genet ; 16(11): e1008968, 2020 11.
Artigo em Inglês | MEDLINE | ID: mdl-33175901

RESUMO

In the two cell divisions of meiosis, diploid genomes are reduced into complementary haploid sets through the discrete, two-step removal of chromosome cohesion, a task carried out in most eukaryotes by protecting cohesion at the centromere until the second division. In eukaryotes without defined centromeres, however, alternative strategies have been innovated. The best-understood of these is found in the nematode Caenorhabditis elegans: after the single off-center crossover divides the chromosome into two segments, or arms, several chromosome-associated proteins or post-translational modifications become specifically partitioned to either the shorter or longer arm, where they promote the correct timing of cohesion loss through as-yet unknown mechanisms. Here, we investigate the meiotic axis HORMA-domain protein HIM-3 and show that it becomes phosphorylated at its C-terminus, within the conserved "closure motif" region bound by the related HORMA-domain proteins HTP-1 and HTP-2. Binding of HTP-2 is abrogated by phosphorylation of the closure motif in in vitro assays, strongly suggesting that in vivo phosphorylation of HIM-3 likely modulates the hierarchical structure of the chromosome axis. Phosphorylation of HIM-3 only occurs on synapsed chromosomes, and similarly to other previously-described phosphorylated proteins of the synaptonemal complex, becomes restricted to the short arm after designation of crossover sites. Regulation of HIM-3 phosphorylation status is required for timely disassembly of synaptonemal complex central elements from the long arm, and is also required for proper timing of HTP-1 and HTP-2 dissociation from the short arm. Phosphorylation of HIM-3 thus plays a role in establishing the identity of short and long arms, thereby contributing to the robustness of the two-step chromosome segregation.


Assuntos
Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/metabolismo , Complexo Sinaptonêmico/metabolismo , Animais , Caenorhabditis elegans/citologia , Caenorhabditis elegans/ultraestrutura , Proteínas de Caenorhabditis elegans/genética , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Proteínas Cromossômicas não Histona/genética , Pareamento Cromossômico , Segregação de Cromossomos , Cromossomos , Meiose/fisiologia , Fosforilação , Prófase/fisiologia , Domínios Proteicos
19.
Genes Dev ; 34(23-24): 1605-1618, 2020 12 01.
Artigo em Inglês | MEDLINE | ID: mdl-33184224

RESUMO

The number of DNA double-strand breaks (DSBs) initiating meiotic recombination is elevated in Saccharomyces cerevisiae mutants that are globally defective in forming crossovers and synaptonemal complex (SC), a protein scaffold juxtaposing homologous chromosomes. These mutants thus appear to lack a negative feedback loop that inhibits DSB formation when homologs engage one another. This feedback is predicted to be chromosome autonomous, but this has not been tested. Moreover, what chromosomal process is recognized as "homolog engagement" remains unclear. To address these questions, we evaluated effects of homolog engagement defects restricted to small portions of the genome using karyotypically abnormal yeast strains with a homeologous chromosome V pair, monosomic V, or trisomy XV. We found that homolog engagement-defective chromosomes incurred more DSBs, concomitant with prolonged retention of the DSB-promoting protein Rec114, while the rest of the genome remained unaffected. SC-deficient, crossover-proficient mutants ecm11 and gmc2 experienced increased DSB numbers diagnostic of homolog engagement defects. These findings support the hypothesis that SC formation provokes DSB protein dissociation, leading in turn to loss of a DSB competent state. Our findings show that DSB number is regulated in a chromosome-autonomous fashion and provide insight into how homeostatic DSB controls respond to aneuploidy during meiosis.


Assuntos
Cromossomos Fúngicos/genética , Quebras de DNA de Cadeia Dupla , Retroalimentação Fisiológica/fisiologia , Meiose/genética , Saccharomyces cerevisiae/genética , Complexo Sinaptonêmico/genética , Aneuploidia , Pareamento Cromossômico/genética , Recombinases/genética , Proteínas de Saccharomyces cerevisiae/genética , Ubiquitina-Proteína Ligases/genética
20.
PLoS One ; 15(10): e0240245, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33017431

RESUMO

Crossover rates and localization are not homogeneous throughout the genomes. Along the chromosomes of almost all species, domains with high crossover rates alternate with domains where crossover rates are significantly lower than the genome-wide average. The distribution of crossovers along chromosomes constitutes the recombination landscape of a given species and can be analyzed at broadscale using immunostaining of the MLH1 protein, a component of mature recombination nodules found on synaptonemal complexes during pachytene. We scored the MLH1 foci in oocytes of the chicken and the guinea fowl and compared their frequencies in the largest bivalents. The average autosomal number of foci is 62 in the chicken and 44 in the guinea fowl. The lower number in the guinea fowl responds to the occurrence of fewer crossovers in the six largest bivalents, where most MLH1 foci occur within one-fifth of the chromosome length with high polarization towards opposite ends. The skewed distribution of foci in the guinea fowl contrast with the more uniform distribution of numerous foci in the chicken, especially in the four largest bivalents. The crossover distribution observed in the guinea fowl is unusual among Galloanserae and also differs from other, more distantly related birds. We discussed the current evidence showing that the shift towards crossover localization, as observed in the guinea fowl, was not a unique event but also occurred at different moments of bird evolution. A comparative analysis of genome-wide average recombination rates in birds shows variations within narrower limits compared to mammals and the absence of a phylogenetic trend.


Assuntos
Proteína 1 Homóloga a MutL/metabolismo , Complexo Sinaptonêmico/metabolismo , Animais , Galinhas , Cariótipo , Oócitos , Filogenia
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