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Dean S. Dawson - One of the best experts on this subject based on the ideXlab platform.
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the pericentromeric heterochromatin of homologous chromosomes remains associated after centromere pairing dissolves in mouse spermatocyte meiosis
Chromosoma, 2019Co-Authors: Craig Eyster, Dean S. Dawson, Roberto J. Pezza, Hoa H Chuong, Chihying LeeAbstract:In 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 to 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 it is unclear how centromere pairing could promote subsequent proper segregation. Here we report that meiotic centromere pairing of chromosomes in mouse spermatocytes allows the formation of an association between chromosome pairs. We find that heterochromatin regions of homologous Centromeres remain associated even after centromere-pairing dissolves. Our results suggest the model that, in mouse spermatocytes, heterochromatin maintains the association of homologous Centromeres in the absence crossing-over.
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heterochromatin interactions maintain homologous centromere associations in mouse spermatocyte meiosis
bioRxiv, 2018Co-Authors: Hoa H Chuong, Dean S. Dawson, Roberto J. Pezza, Craig Eyster, Chihying LeeAbstract:Summary In 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.
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Synaptonemal Complex Components Persist at Centromeres and Are Required for Homologous Centromere Pairing in Mouse Spermatocytes
PLOS Genetics, 2012Co-Authors: C. Gastón Bisig, Michel F. Guiraldelli, Anna Kouznetsova, Harry Scherthan, Dean S. Dawson, Christer Hoog, Roberto J. PezzaAbstract:Recent studies in simple model organisms have shown that centromere pairing is important for ensuring high-fidelity meiotic chromosome segregation. However, this process and the mechanisms regulating it in higher eukaryotes are unknown. Here we present the first detailed study of meiotic centromere pairing in mouse spermatogenesis and link it with key events of the G2/metaphase I transition. In mouse we observed no evidence of the persistent coupling of Centromeres that has been observed in several model organisms. We do however find that telomeres associate in non-homologous pairs or small groups in B type spermatogonia and pre-leptotene spermatocytes, and this association is disrupted by deletion of the synaptonemal complex component SYCP3. Intriguingly, we found that, in mid prophase, chromosome synapsis is not initiated at Centromeres, and centromeric regions are the last to pair in the zygotene-pachytene transition. In late prophase, we first identified the proteins that reside at paired Centromeres. We found that components of the central and lateral element and transverse filaments of the synaptonemal complex are retained at paired Centromeres after disassembly of the synaptonemal complex along diplotene chromosome arms. The absence of SYCP1 prevents centromere pairing in knockout mouse spermatocytes. The localization dynamics of SYCP1 and SYCP3 suggest that they play different roles in promoting homologous centromere pairing. SYCP1 remains only at paired Centromeres coincident with the time at which some kinetochore proteins begin loading at Centromeres, consistent with a role in assembly of meiosis-specific kinetochores. After removal of SYCP1 from Centromeres, SYCP3 then accumulates at paired Centromeres where it may promote bi-orientation of homologous Centromeres. We propose that, in addition to their roles as synaptonemal complex components, SYCP1 and SYCP3 act at the Centromeres to promote the establishment and/or maintenance of centromere pairing and, by doing so, improve the segregation fidelity of mammalian meiotic chromosomes.
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the synaptonemal complex protein zip1 promotes bi orientation of Centromeres at meiosis i
PLOS Genetics, 2009Co-Authors: Dean S. Dawson, Mara N Gladstone, David Obeso, Hoa ChuongAbstract:In meiosis I, homologous chromosomes become paired and then separate from one another to opposite poles of the spindle. In humans, errors in this process are a leading cause of birth defects, mental retardation, and infertility. In most organisms, crossing-over, or exchange, between the homologous partners provides a link that promotes their proper, bipolar, attachment to the spindle. Attachment of both partners to the same pole can sometimes be corrected during a delay that is triggered by the spindle checkpoint. Studies of non-exchange chromosomes have shown that centromere pairing serves as an alternative to exchange by orienting the Centromeres for proper microtubule attachment. Here, we demonstrate a new role for the synaptonemal complex protein Zip1. Zip1 localizes to the Centromeres of non-exchange chromosomes in pachytene and mediates centromere pairing and segregation of the partners at meiosis I. Exchange chromosomes were also found to experience Zip1-dependent pairing at their Centromeres. Zip1 was found to persist at Centromeres, after synaptonemal complex disassembly, remaining there until microtubule attachment. Disruption of this centromere pairing, in spindle checkpoint mutants, randomized the segregation of exchange chromosomes. These results demonstrate that Zip1-mediated pairing of exchange chromosome Centromeres promotes an initial, bipolar attachment of microtubules. This activity of Zip1 lessens the load on the spindle checkpoint, greatly reducing the chance that the cell will exit the checkpoint delay with an improperly oriented chromosome pair. Thus exchange, the spindle checkpoint, and centromere pairing are complementary mechanisms that ensure the proper segregation of homologous partners at meiosis I.
Kaustuv Sanyal - One of the best experts on this subject based on the ideXlab platform.
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Functional and Comparative Analysis of Centromeres Reveals Clade-Specific Genome Rearrangements in Candida auris and a Chromosome Number Change in Related Species.
mBio, 2021Co-Authors: Aswathy Narayanan, Rahul Siddharthan, Promit Ganguly, Rakesh Netha Vadnala, Pavitra Selvakumar, Shivaprakash M. Rudramurthy, Rajendra Prasad, Arunaloke Chakrabarti, Kaustuv SanyalAbstract:ABSTRACT The thermotolerant multidrug-resistant ascomycete Candida auris rapidly emerged since 2009 causing systemic infections worldwide and simultaneously evolved in different geographical zones. The molecular events that orchestrated this sudden emergence of the killer fungus remain mostly elusive. Here, we identify Centromeres in C. auris and related species, using a combined approach of chromatin immunoprecipitation and comparative genomic analyses. We find that C. auris and multiple other species in the Clavispora/Candida clade shared a conserved small regional GC-poor centromere landscape lacking periCentromeres or repeats. Further, a centromere inactivation event led to karyotypic alterations in this species complex. Interspecies genome analysis identified several structural chromosomal changes around Centromeres. In addition, Centromeres are found to be rapidly evolving loci among the different geographical clades of the same species of C. auris. Finally, we reveal an evolutionary trajectory of the unique karyotype associated with clade 2 that consists of the drug-susceptible isolates of C. auris. IMPORTANCECandida auris, the killer fungus, emerged as different geographical clades, exhibiting multidrug resistance and high karyotype plasticity. Chromosomal rearrangements are known to play key roles in the emergence of new species, virulence, and drug resistance in pathogenic fungi. Centromeres, the genomic loci where microtubules attach to separate the sister chromatids during cell division, are known to be hot spots of breaks and downstream rearrangements. We identified the Centromeres in C. auris and related species to study their involvement in the evolution and karyotype diversity reported in C. auris. We report conserved centromere features in 10 related species and trace the events that occurred at the Centromeres during evolution. We reveal a centromere inactivation-mediated chromosome number change in these closely related species. We also observe that one of the geographical clades, the East Asian clade, evolved along a unique trajectory, compared to the other clades and related species.
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cellular dynamics and genomic identity of Centromeres in cereal blast fungus
Mbio, 2019Co-Authors: Vikas Yadav, Kaustuv Sanyal, Fan Yang, Md Hashim Reza, Sanzhen Liu, Barbara Valent, Naweed I NaqviAbstract:ABSTRACT Precise kinetochore-microtubule interactions ensure faithful chromosome segregation in eukaryotes. Centromeres, identified as scaffolding sites for kinetochore assembly, are among the most rapidly evolving chromosomal loci in terms of the DNA sequence and length and organization of intrinsic elements. Neither the centromere structure nor the kinetochore dynamics is well studied in plant-pathogenic fungi. Here, we sought to understand the process of chromosome segregation in the rice blast fungus Magnaporthe oryzae. High-resolution imaging of green fluorescent protein (GFP)-tagged inner kinetochore proteins CenpA and CenpC revealed unusual albeit transient declustering of Centromeres just before anaphase separation of chromosomes in M. oryzae. Strikingly, the declustered Centromeres positioned randomly at the spindle midzone without an apparent metaphase plate per se. Using CenpA chromatin immunoprecipitation followed by deep sequencing, all seven Centromeres in M. oryzae were found to be regional, spanning 57-kb to 109-kb transcriptionally poor regions. Highly AT-rich and heavily methylated DNA sequences were the only common defining features of all the Centromeres in rice blast. Lack of centromere-specific DNA sequence motifs or repetitive elements suggests an epigenetic specification of centromere function in M. oryzae. PacBio genome assemblies and synteny analyses facilitated comparison of the centromeric/pericentromeric regions in distinct isolates of rice blast and wheat blast and in Magnaporthiopsis poae. Overall, this study revealed unusual centromere dynamics and precisely identified the centromere loci in the top model fungal pathogens that belong to Magnaporthales and cause severe losses in the global production of food crops and turf grasses. IMPORTANCEMagnaporthe oryzae is an important fungal pathogen that causes a loss of 10% to 30% of the annual rice crop due to the devastating blast disease. In most organisms, kinetochores are clustered together or arranged at the metaphase plate to facilitate synchronized anaphase separation of sister chromatids in mitosis. In this study, we showed that the initially clustered kinetochores separate and position randomly prior to anaphase in M. oryzae. Centromeres in M. oryzae occupy large genomic regions and form on AT-rich DNA without any common sequence motifs. Overall, this study identified atypical kinetochore dynamics and mapped functional Centromeres in M. oryzae to define the roles of centromeric and pericentric boundaries in kinetochore assembly on epigenetically specified centromere loci. This study should pave the way for further understanding of the contribution of heterochromatin in genome stability and virulence of the blast fungus and its related species of high economic importance.
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cellular dynamics and genomic identity of Centromeres in rice blast
bioRxiv, 2018Co-Authors: Vikas Yadav, Kaustuv Sanyal, Fan Yang, Md Hashim Reza, Naweed I NaqviAbstract:A series of well-synchronized events mediated by kinetochore-microtubule interactions ensure faithful chromosome segregation in eukaryotes. Centromeres scaffold kinetochore assembly and are among the fastest evolving chromosomal loci in terms of the DNA sequence, length, and organization of intrinsic elements. Neither the centromere structure nor the kinetochore dynamics are well studied in plant pathogenic fungi. Here, we sought to understand the process of chromosome segregation in the rice blast fungus, Magnaporthe oryzae. High-resolution confocal imaging of GFP-tagged inner kinetochore proteins, CenpA and CenpC, revealed an unusual albeit transient declustering of Centromeres just before anaphase separation in M. oryzae. Strikingly, the declustered Centromeres positioned randomly at the spindle midzone without an apparent metaphase plate per se. Using chromatin immunoprecipitation followed by deep sequencing, all seven Centromeres were identified as CenpA-rich regions in the wild-type Guy11 strain of M. oryzae. The Centromeres in M. oryzae are regional and span 57 to 109 kb transcriptionally poor regions. No centromere-specific DNA sequence motif or repetitive elements could be identified in these regions suggesting an epigenetic specification of centromere function in M. oryzae. Highly AT-rich and heavily methylated DNA sequences were the only common defining features of all the Centromeres in the Rice Blast. Detailed gene synteny analyses helped identify and compare the centromere regions in distinct isolates of M. oryzae and its related species Magnaporthe poae. Overall, this study identifies unusual centromere dynamics and maps the centromere DNA sequences in the top model fungal pathogen M. oryzae, which causes severe losses in global rice production.
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rnai is a critical determinant of centromere evolution in closely related fungi
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Vikas Yadav, Lake R Illmyre, Hagya C Thimmappa, Terrance Shea, Robe E Lintne, Guus Akkere, Christina A Cuomo, Joseph Heitma, Kaustuv SanyalAbstract:The centromere DNA locus on a eukaryotic chromosome facilitates faithful chromosome segregation. Despite performing such a conserved function, centromere DNA sequence as well as the organization of sequence elements is rapidly evolving in all forms of eukaryotes. The driving force that facilitates centromere evolution remains an enigma. Here, we studied the evolution of Centromeres in closely related species in the fungal phylum of Basidiomycota. Using ChIP-seq analysis of conserved inner kinetochore proteins, we identified Centromeres in three closely related Cryptococcus species: two of which are RNAi-proficient, while the other lost functional RNAi. We find that the Centromeres in the RNAi-deficient species are significantly shorter than those of the two RNAi-proficient species. While Centromeres are LTR retrotransposon-rich in all cases, the RNAi-deficient species lost all full-length retroelements from its Centromeres. In addition, Centromeres in RNAi-proficient species are associated with a significantly higher level of cytosine DNA modifications compared with those of RNAi-deficient species. Furthermore, when an RNAi-proficient Cryptococcus species and its RNAi-deficient mutants were passaged under similar conditions, the centromere length was found to be occasionally shortened in RNAi mutants. In silico analysis of predicted Centromeres in a group of closely related Ustilago species, also belonging to the Basidiomycota, were found to have undergone a similar transition in the centromere length in an RNAi-dependent fashion. Based on the correlation found in two independent basidiomycetous species complexes, we present evidence suggesting that the loss of RNAi and cytosine DNA methylation triggered transposon attrition, which resulted in shortening of centromere length during evolution.
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Five key determinants of centromere identity in pathogenic fungi.
2018Co-Authors: Vikas Yadav, Krishnendu Guin, Lakshmi Sreekumar, Kaustuv SanyalAbstract:(A) The length and type of Centromeres in various pathogenic fungi have been depicted in a cladogram. Candida glabrata and Malassezia sympodialis have point Centromeres (blue); C. albicans, C. tropicalis, and Cryptococcus deuterogattii have small regional Centromeres (green); and C. neoformans and C. deneoformans harbor large regional repetitive Centromeres (pink). (B) Centromeric heterochromatin or centrochromatin refers to the various chemical modifications associated with the histones (both canonical and variant) as well as DNA at the centromeric locus. For example, centromere DNA is methylated at cytosines, and CENP-A nucleosomes are interspersed with H3K9-dimethylated nucleosomes in C. neoformans. (C) Transcription and a functional RNAi machinery at the centromere are required to preserve centromere identity in some organisms. The Centromeres in the Ustilago and Cryptococcus species complexes are poorly transcribed. In C. neoformans, centromeric transcription is regulated by the RNAi machinery that silences centromeric retrotransposons to stabilize centromere structure. Unprocessed long noncoding RNA, whose function is unknown, is also produced from Centromeres in this species. (D) DNA replication and repair proteins are known to play a key role in C. albicans centromere stability. The centromere proximal origins help in maintaining centromere function in this organism. Replication forks converging toward the centromere stall randomly, which leads to accumulation of single-stranded DNA (ssDNA) that recruits repair proteins like Rad51 and Rad52, along with new CENP-A molecules in C. albicans. (E) The spatial location of Centromeres within the nucleus determines its activity and interaction with other nuclear subcompartments. All Centromeres are clustered toward the nuclear periphery to form a CENP-A–rich zone in C. albicans and many other pathogenic fungi. This preferential spatial distribution helps to determine the site of centromere assembly in every cell cycle. CENP-A, centromere protein A; H3K9, histone H3 lysine 9; Rad, radiation sensitive; RNAi, RNA interference; ssDNA, single-stranded DNA.
Ben E. Black - One of the best experts on this subject based on the ideXlab platform.
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the unique kind of human artificial chromosome bypassing the requirement for repetitive centromere dna
Experimental Cell Research, 2020Co-Authors: Craig W Gambogi, Glennis A Logsdon, Jennine M Dawickimckenna, Ben E. BlackAbstract:Abstract Centromeres are essential components of all eukaryotic chromosomes, including artificial/synthetic ones built in the laboratory. In humans, Centromeres are typically located on repetitive α-satellite DNA, and these sequences are the “major ingredient” in first-generation human artificial chromosomes (HACs). Repetitive centromeric sequences present a major challenge for the design of synthetic mammalian chromosomes because they are difficult to synthesize, assemble, and characterize. Additionally, in most eukaryotes, Centromeres are defined epigenetically. Here, we review the role of the genetic and epigenetic contributions to establishing centromere identity, highlighting recent work to hijack the epigenetic machinery to initiate centromere identity on a new generation of HACs built without α-satellite DNA. We also discuss the opportunities and challenges in developing useful unique sequence-based HACs.
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expanded satellite repeats amplify a discrete cenp a nucleosome assembly site on chromosomes that drive in female meiosis
Current Biology, 2017Co-Authors: Aiko Iwataotsubo, Lukas Chmatal, Richard M. Schultz, Samantha J Falk, Jennine M Dawickimckenna, Takashi Akera, Michael A Lampson, Karren Yang, Beth A Sullivan, Ben E. BlackAbstract:Female meiosis provides an opportunity for selfish genetic elements to violate Mendel's law of segregation by increasing the chance of segregating to the egg [1]. Centromeres and other repetitive sequences can drive in meiosis by cheating the segregation process [2], but the underlying mechanisms are unknown. Here, we show that Centromeres with more satellite repeats house more nucleosomes that confer centromere identity, containing the histone H3 variant CENP-A, and bias their segregation to the egg relative to Centromeres with fewer repeats. CENP-A nucleosomes predominantly occupy a single site within the repeating unit that becomes limiting for centromere assembly on smaller Centromeres. We propose that amplified repetitive sequences act as selfish elements by promoting expansion of CENP-A chromatin and increased transmission through the female germline.
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cenp a modifications on ser68 and lys124 are dispensable for establishment maintenance and long term function of human Centromeres
Developmental Cell, 2017Co-Authors: Daniele Fachinetti, Glennis A Logsdon, Don W Cleveland, Amira Abdullah, Evan B Selzer, Ben E. BlackAbstract:CENP-A is a histone H3 variant key to epigenetic specification of mammalian Centromeres. Using transient overexpression of CENP-A mutants, two recent reports in Developmental Cell proposed essential centromere functions for post-translational modifications of human CENP-A. Phosphorylation at Ser68 was proposed to have an essential role in CENP-A deposition at Centromeres. Blockage of ubiquitination at Lys124 was proposed to abrogate localization of CENP-A to the centromere. Following gene inactivation and replacement in human cells, we demonstrate that CENP-A mutants that cannot be phosphorylated at Ser68 or ubiquitinated at Lys124 assemble efficiently at Centromeres during G1, mediate early events in centromere establishment at an ectopic chromosomal locus, and maintain centromere function indefinitely. Thus, neither Ser68 nor Lys124 post-translational modification is essential for long-term centromere identity, propagation, cell-cycle-dependent deposition, maintenance, function, or mediation of early steps in centromere establishment.
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long term retention of cenp a nucleosomes in mammalian oocytes underpins transgenerational inheritance of centromere identity
Current Biology, 2016Co-Authors: Evan M Smoak, Richard M. Schultz, Michael A Lampson, Paula Stein, Ben E. BlackAbstract:Centromeres control genetic inheritance by directing chromosome segregation but are not genetically encoded themselves. Rather, Centromeres are defined by nucleosomes containing CENP-A, a histone H3 variant [1]. In cycling somatic cells, centromere identity is maintained by an established cell-cycle-coupled CENP-A chromatin assembly pathway, but how Centromeres are inherited through the mammalian female germline is unclear because of the long (months to decades) prophase I arrest. Here we show that mouse oocytes retain the pool of CENP-A nucleosomes assembled before birth, and that this pool is sufficient for centromere function, fertility, and genome transmission to embryos. Indeed, oocytes lack any measurable CENP-A nucleosome assembly through the entire fertile lifespan of the female (>1 year). Thus, the remarkable stability of CENP-A nucleosomes confers transgenerational centromere identity in mammals.
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assembly in g1 phase and long term stability are unique intrinsic features of cenp a nucleosomes
Molecular Biology of the Cell, 2013Co-Authors: Dani L Bodor, Ben E. Black, Luis P Valente, Joao F Mata, Lars E T JansenAbstract:Centromeres are the site of kinetochore formation during mitosis. Centromere protein A (CENP-A), the centromere-specific histone H3 variant, is essential for the epigenetic maintenance of centromere position. Previously we showed that newly synthesized CENP-A is targeted to Centromeres exclusively during early G1 phase and is subsequently maintained across mitotic divisions. Using SNAP-based fluorescent pulse labeling, we now demonstrate that cell cycle–restricted chromatin assembly at Centromeres is unique to CENP-A nucleosomes and does not involve assembly of other H3 variants. Strikingly, stable retention is restricted to the CENP-A/H4 core of the nucleosome, which we find to outlast general chromatin across several cell divisions. We further show that cell cycle timing of CENP-A assembly is independent of centromeric DNA sequences and instead is mediated by the CENP-A targeting domain. Unexpectedly, this domain also induces stable transmission of centromeric nucleosomes, independent of the CENP-A deposition factor HJURP. This demonstrates that intrinsic properties of the CENP-A protein direct its cell cycle–restricted assembly and induces quantitative mitotic transmission of the CENP-A/H4 nucleosome core, ensuring long-term stability and epigenetic maintenance of centromere position.
Roberto J. Pezza - One of the best experts on this subject based on the ideXlab platform.
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the pericentromeric heterochromatin of homologous chromosomes remains associated after centromere pairing dissolves in mouse spermatocyte meiosis
Chromosoma, 2019Co-Authors: Craig Eyster, Dean S. Dawson, Roberto J. Pezza, Hoa H Chuong, Chihying LeeAbstract:In 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 to 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 it is unclear how centromere pairing could promote subsequent proper segregation. Here we report that meiotic centromere pairing of chromosomes in mouse spermatocytes allows the formation of an association between chromosome pairs. We find that heterochromatin regions of homologous Centromeres remain associated even after centromere-pairing dissolves. Our results suggest the model that, in mouse spermatocytes, heterochromatin maintains the association of homologous Centromeres in the absence crossing-over.
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heterochromatin interactions maintain homologous centromere associations in mouse spermatocyte meiosis
bioRxiv, 2018Co-Authors: Hoa H Chuong, Dean S. Dawson, Roberto J. Pezza, Craig Eyster, Chihying LeeAbstract:Summary In 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.
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Synaptonemal Complex Components Persist at Centromeres and Are Required for Homologous Centromere Pairing in Mouse Spermatocytes
PLOS Genetics, 2012Co-Authors: C. Gastón Bisig, Michel F. Guiraldelli, Anna Kouznetsova, Harry Scherthan, Dean S. Dawson, Christer Hoog, Roberto J. PezzaAbstract:Recent studies in simple model organisms have shown that centromere pairing is important for ensuring high-fidelity meiotic chromosome segregation. However, this process and the mechanisms regulating it in higher eukaryotes are unknown. Here we present the first detailed study of meiotic centromere pairing in mouse spermatogenesis and link it with key events of the G2/metaphase I transition. In mouse we observed no evidence of the persistent coupling of Centromeres that has been observed in several model organisms. We do however find that telomeres associate in non-homologous pairs or small groups in B type spermatogonia and pre-leptotene spermatocytes, and this association is disrupted by deletion of the synaptonemal complex component SYCP3. Intriguingly, we found that, in mid prophase, chromosome synapsis is not initiated at Centromeres, and centromeric regions are the last to pair in the zygotene-pachytene transition. In late prophase, we first identified the proteins that reside at paired Centromeres. We found that components of the central and lateral element and transverse filaments of the synaptonemal complex are retained at paired Centromeres after disassembly of the synaptonemal complex along diplotene chromosome arms. The absence of SYCP1 prevents centromere pairing in knockout mouse spermatocytes. The localization dynamics of SYCP1 and SYCP3 suggest that they play different roles in promoting homologous centromere pairing. SYCP1 remains only at paired Centromeres coincident with the time at which some kinetochore proteins begin loading at Centromeres, consistent with a role in assembly of meiosis-specific kinetochores. After removal of SYCP1 from Centromeres, SYCP3 then accumulates at paired Centromeres where it may promote bi-orientation of homologous Centromeres. We propose that, in addition to their roles as synaptonemal complex components, SYCP1 and SYCP3 act at the Centromeres to promote the establishment and/or maintenance of centromere pairing and, by doing so, improve the segregation fidelity of mammalian meiotic chromosomes.
Iain M Cheeseman - One of the best experts on this subject based on the ideXlab platform.
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alpha satellite rna transcripts are repressed by centromere nucleolus associations
eLife, 2020Co-Authors: Leah Bury, Brittania Moodie, Liliana S Mckay, Karen H Miga, Iain M CheesemanAbstract:Although originally thought to be silent chromosomal regions, Centromeres are instead actively transcribed. However, the behavior and contributions of centromere-derived RNAs have remained unclear. Here, we used single-molecule fluorescence in-situ hybridization (smFISH) to detect alpha-satellite RNA transcripts in intact human cells. We find that alpha-satellite RNA-smFISH foci levels vary across cell lines and over the cell cycle, but do not remain associated with Centromeres, displaying localization consistent with other long non-coding RNAs. Alpha-satellite expression occurs through RNA polymerase II-dependent transcription, but does not require established centromere or cell division components. Instead, our work implicates centromere-nucleolar interactions as repressing alpha-satellite expression. The fraction of nucleolar-localized Centromeres inversely correlates with alpha-satellite transcripts levels across cell lines and transcript levels increase substantially when the nucleolus is disrupted. The control of alpha-satellite transcripts by centromere-nucleolar contacts provides a mechanism to modulate centromere transcription and chromatin dynamics across diverse cell states and conditions.
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alpha satellite rna transcripts are repressed by centromere nucleolus associations
bioRxiv, 2020Co-Authors: Leah Bury, Brittania Moodie, Liliana S Mckay, Karen H Miga, Iain M CheesemanAbstract:Centromeres play a fundamental role in chromosome segregation. Although originally thought to be silent chromosomal regions, Centromeres are actively transcribed. However, the behavior and contributions of centromere-derived RNAs have remained unclear. Here, we used single-molecule fluorescence in-situ hybridization (smFISH) to detect alpha-satellite RNA transcripts in intact human cells. We find that alpha-satellite RNA smFISH foci fluctuate in their levels over the cell cycle and do not remain associated with Centromeres, displaying localization consistent with other long non-coding RNAs. Our results demonstrate that alpha-satellite expression occurs through RNA Polymerase II-dependent transcription, but does not require centromere proteins and other cell division components. Instead, our work implicates centromere-nucleolar associations as the major factor regulating alpha-satellite expression. The fraction of nucleolar-localized Centromeres inversely correlates with alpha-satellite transcripts levels, explaining variations in alpha-satellite RNA between cell lines. In addition, alpha-satellite transcript levels increase substantially when the nucleolus is disrupted. Together, our results are inconsistent with a direct, physical role for alpha-satellite transcripts in cell division processes, and instead support a role for ongoing transcription in promoting centromere chromatin dynamics. The control of alpha-satellite transcription by centromere-nucleolar contacts provides a mechanism to modulate centromere transcription and chromatin dynamics across diverse cell states and conditions.