The centromere is the chromosome region where microtubules attach during cell division. In contrast to monocentric chromosomes with one centromere, holocentric species usually distribute hundreds of centromere units along the entire chromatid. We assembled the chromosome-scale reference genome and analyzed the holocentromere and (epi)genome organization of the lilioid Chionographis japonica. Remarkably, each of its holocentric chromatids consists of only 7 to 11 evenly spaced megabase-sized centromere-specific histone H3-positive units. These units contain satellite arrays of 23 and 28 bp-long monomers capable of forming palindromic structures. Like monocentric species, C. japonica forms clustered centromeres in chromocenters at interphase. In addition, the large-scale eu- and heterochromatin arrangement differs between C. japonica and other known holocentric species. Finally, using polymer simulations, we model the formation of prometaphase line-like holocentromeres from interphase centromere clusters. Our findings broaden the knowledge about centromere diversity, showing that holocentricity is not restricted to species with numerous and small centromere units.
Chromatids of mitotic chromosomes were suggested to coil into a helix in early cytological studies and this assumption was recently supported by chromosome conformation capture (3C) sequencing. Still, direct differential visualization of a condensed chromatin fibre confirming the helical model was lacking. Here, we combined Hi-C analysis of purified metaphase chromosomes, biopolymer modelling and spatial structured illumination microscopy of large fluorescently labeled chromosome segments to reveal the chromonema - a helically-wound, 400 nm thick chromatin thread forming barley mitotic chromatids. Chromatin from adjacent turns of the helix intermingles due to the stochastic positioning of chromatin loops inside the chromonema. Helical turn size varies along chromosome length, correlating with chromatin density. Constraints on the observable dimensions of sister chromatid exchanges further supports the helical chromonema model.
Receiving complete and undamaged genetic information is vital for the survival of daughter cells after chromosome segregation. The most critical steps in this process are accurate DNA replication during S phase and a faithful chromosome segregation during anaphase. Any errors in DNA replication or chromosome segregation have dire consequences, since cells arising after division might have either changed or incomplete genetic information. Accurate chromosome segregation during anaphase requires a protein complex called cohesin, which holds together sister chromatids. This complex unifies sister chromatids from their synthesis during S phase, until separation in anaphase. Upon entry into mitosis, the spindle apparatus is assembled, which eventually engages kinetochores of all chromosomes. Additionally, when kinetochores of sister chromatids assume amphitelic attachment to the spindle microtubules, cells are finally ready for the separation of sister chromatids. This is achieved by the enzymatic cleavage of cohesin subunits Scc1 or Rec8 by an enzyme called Separase. After cohesin cleavage, sister chromatids remain attached to the spindle apparatus and their poleward movement on the spindle is initiated. The removal of cohesion between sister chromatids is an irreversible step and therefore it must be synchronized with assembly of the spindle apparatus, since precocious separation of sister chromatids might lead into aneuploidy and tumorigenesis. In this review, we focus on recent discoveries concerning the regulation of Separase activity during the cell cycle.
- Klíčová slova
- CDK1, Cyclin B1, Mad2, Sgo2, aneuploidy, chromosome division, cohesin, securin, segregation errors, separase,
- MeSH
- anafáze * MeSH
- aparát dělícího vřeténka metabolismus MeSH
- chromatidy * metabolismus MeSH
- mitóza MeSH
- proteiny buněčného cyklu metabolismus MeSH
- segregace chromozomů MeSH
- separáza genetika metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
- Názvy látek
- proteiny buněčného cyklu MeSH
- separáza MeSH
Chromatin-based processes are essential for cellular functions. Structural maintenance of chromosomes (SMCs) are evolutionarily conserved molecular machines that organize chromosomes throughout the cell cycle, mediate chromosome compaction, promote DNA repair, or control sister chromatid attachment. The SMC5/6 complex is known for its pivotal role during the maintenance of genome stability. However, a dozen recent plant studies expanded the repertoire of SMC5/6 complex functions to the entire plant sexual reproductive phase. The SMC5/6 complex is essential in meiosis, where its activity must be precisely regulated to allow for normal meiocyte development. Initially, it is attenuated by the recombinase RAD51 to allow for efficient strand invasion by the meiosis-specific recombinase DMC1. At later stages, it is essential for the normal ratio of interfering and non-interfering crossovers, detoxifying aberrant joint molecules, preventing chromosome fragmentation, and ensuring normal chromosome/sister chromatid segregation. The latter meiotic defects lead to the production of diploid male gametes in Arabidopsis SMC5/6 complex mutants, increased seed abortion, and production of triploid offspring. The SMC5/6 complex is directly involved in controlling normal embryo and endosperm cell divisions, and pioneer studies show that the SMC5/6 complex is also important for seed development and normal plant growth in cereals.
- Klíčová slova
- SMC5/6 complex, fertility, genome stability, meiosis, polyploidy, reproductive development, seed,
- MeSH
- Arabidopsis * genetika metabolismus MeSH
- chromatidy metabolismus MeSH
- meióza MeSH
- oprava DNA MeSH
- proteiny buněčného cyklu * genetika metabolismus MeSH
- rekombinasy genetika MeSH
- rozmnožování genetika MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
- Názvy látek
- proteiny buněčného cyklu * MeSH
- rekombinasy MeSH
Young sex chromosomes possess unique and ongoing dynamics that allow us to understand processes that have an impact on their evolution and divergence. The genus Silene includes species with evolutionarily young sex chromosomes, and two species of section Melandrium, namely Silene latifolia (24, XY) and Silene dioica (24, XY), are well-established models of sex chromosome evolution, Y chromosome degeneration, and sex determination. In both species, the X and Y chromosomes are strongly heteromorphic and differ in the genomic composition compared to the autosomes. It is generally accepted that for proper cell division, the longest chromosomal arm must not exceed half of the average length of the spindle axis at telophase. Yet, it is not clear what are the dynamics between males and females during mitosis and how the cell compensates for the presence of the large Y chromosome in one sex. Using hydroxyurea cell synchronization and 2D/3D microscopy, we determined the position of the sex chromosomes during the mitotic cell cycle and determined the upper limit for the expansion of sex chromosome non-recombining region. Using 3D specimen preparations, we found that the velocity of the large chromosomes is compensated by the distant positioning from the central interpolar axis, confirming previous mathematical modulations.
- Klíčová slova
- Silene, central interpolar axis, chromosome velocity, sex chromosomes, sister chromatid division,
- MeSH
- chromatidy fyziologie MeSH
- chromozomy rostlin fyziologie MeSH
- hybridizace in situ fluorescenční MeSH
- hydroxymočovina farmakologie MeSH
- konfokální mikroskopie MeSH
- mitóza MeSH
- molekulární evoluce MeSH
- pohlavní chromozomy fyziologie MeSH
- Silene genetika fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- hydroxymočovina MeSH
Crossing over, in addition to its strictly genetic role, also performs a critical mechanical function, by bonding homologues in meiosis. Hence, it is responsible for an orderly reduction of the chromosome number. As such, it is strictly controlled in frequency and distribution. The well-known crossover control is positive crossover interference which reduces the probability of a crossover in the vicinity of an already formed crossover. A poorly studied aspect of the control is chromatid interference. Such analyses are possible in very few organisms as they require observation of all four products of a single meiosis. Here, we provide direct evidence of chromatid interference. Using in situ probing in two interspecific plant hybrids (Lolium multiflorum×Festuca pratensis and Allium cepa×A. roylei) during anaphase I, we demonstrate that the involvement of four chromatids in double crossovers is significantly more frequent than expected (64% versus 25%). We also provide a physical measure of the crossover interference distance, covering ~30-40% of the relative chromosome arm length, and show that the centromere acts as a barrier for crossover interference. The two arms of a chromosome appear to act as independent units in the process of crossing over. Chromatid interference has to be seriously addressed in genetic mapping approaches and further studies.
- Klíčová slova
- Centromere, chromatid interference, crossover interference, homoeologous chromosome, hybrid, meiosis, recombination,
- MeSH
- česneky MeSH
- chromatidy genetika MeSH
- crossing over (genetika) MeSH
- Festuca * genetika MeSH
- jílek * genetika MeSH
- meióza genetika MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
ISWI chromatin remodeling ATPase SMARCA5 (SNF2H) is a well-known factor for its role in regulation of DNA access via nucleosome sliding and assembly. SMARCA5 transcriptionally inhibits the myeloid master regulator PU.1. Upregulation of SMARCA5 was previously observed in CD34+ hematopoietic progenitors of acute myeloid leukemia (AML) patients. Since high levels of SMARCA5 are necessary for intensive cell proliferation and cell cycle progression of developing hematopoietic stem and progenitor cells in mice, we reasoned that removal of SMARCA5 enzymatic activity could affect the cycling or undifferentiated state of leukemic progenitor-like clones. Indeed, we observed that CRISPR/cas9-mediated SMARCA5 knockout in AML cell lines (S5KO) inhibited the cell cycle progression. We also observed that the SMARCA5 deletion induced karyorrhexis and nuclear budding as well as increased the ploidy, indicating its role in mitotic division of AML cells. The cytogenetic analysis of S5KO cells revealed the premature chromatid separation. We conclude that deleting SMARCA5 in AML blocks leukemic proliferation and chromatid cohesion.
- Klíčová slova
- AML, CRISPR, SMARCA5, SNF2H, leukemia, therapeutic target,
- MeSH
- adenosintrifosfatasy nedostatek metabolismus MeSH
- akutní myeloidní leukemie * enzymologie genetika patologie MeSH
- buňky K562 MeSH
- chromatidy * genetika metabolismus MeSH
- chromozomální proteiny, nehistonové nedostatek metabolismus MeSH
- genový knockout * MeSH
- lidé MeSH
- nádorové buněčné linie MeSH
- nádorové proteiny * nedostatek metabolismus MeSH
- proliferace buněk * MeSH
- Check Tag
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- adenosintrifosfatasy MeSH
- chromozomální proteiny, nehistonové MeSH
- nádorové proteiny * MeSH
- SMARCA5 protein, human MeSH Prohlížeč
Chromosomal rearrangements (e.g., fusions/fissions) have the potential to drive speciation. However, their accumulation in a population is generally viewed as unlikely, because chromosomal heterozygosity should lead to meiotic problems and aneuploid gametes. Canonical meiosis involves segregation of homologous chromosomes in meiosis I and sister chromatid segregation during meiosis II. In organisms with holocentric chromosomes, which are characterized by kinetic activity distributed along almost the entire chromosome length, this order may be inverted depending on their metaphase I orientation. Here we analyzed the evolutionary role of this intrinsic versatility of holocentric chromosomes, which is not available to monocentric ones, by studying F1 to F4 hybrids between two chromosomal races of the Wood White butterfly (Leptidea sinapis), separated by at least 24 chromosomal fusions/fissions. We found that these chromosomal rearrangements resulted in multiple meiotic multivalents, and, contrary to the theoretical prediction, the hybrids displayed relatively high reproductive fitness (42% of that of the control lines) and regular behavior of meiotic chromosomes. In the hybrids, we also discovered inverted meiosis, in which the first and critical stage of chromosome number reduction was replaced by the less risky stage of sister chromatid separation. We hypothesize that the ability to invert the order of the main meiotic events facilitates proper chromosome segregation and hence rescues fertility and viability in chromosomal hybrids, potentially promoting dynamic karyotype evolution and chromosomal speciation.
- Klíčová slova
- chromosomal evolution, chromosomal rearrangement, hybridization, inverted meiosis, speciation,
- MeSH
- chiméra * genetika metabolismus MeSH
- chromatidy * genetika metabolismus MeSH
- chromozomy hmyzu genetika metabolismus MeSH
- metafáze fyziologie MeSH
- motýli * genetika metabolismus MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Replication across damaged DNA templates is accompanied by transient formation of sister chromatid junctions (SCJs). Cells lacking Esc2, an adaptor protein containing no known enzymatic domains, are defective in the metabolism of these SCJs. However, how Esc2 is involved in the metabolism of SCJs remains elusive. Here we show interaction between Esc2 and a structure-specific endonuclease Mus81-Mms4 (the Mus81 complex), their involvement in the metabolism of SCJs, and the effects Esc2 has on the enzymatic activity of the Mus81 complex. We found that Esc2 specifically interacts with the Mus81 complex via its SUMO-like domains, stimulates enzymatic activity of the Mus81 complex in vitro, and is involved in the Mus81 complex-dependent resolution of SCJs in vivo Collectively, our data point to the possibility that the involvement of Esc2 in the metabolism of SCJs is, in part, via modulation of the activity of the Mus81 complex.
- MeSH
- chromatidy chemie metabolismus MeSH
- DNA fungální genetika metabolismus MeSH
- DNA vazebné proteiny chemie genetika metabolismus MeSH
- endonukleasy chemie genetika metabolismus MeSH
- Escherichia coli genetika metabolismus MeSH
- jaderné proteiny chemie genetika metabolismus MeSH
- klonování DNA MeSH
- křížová struktura DNA chemie metabolismus MeSH
- malé modifikační proteiny související s ubikvitinem chemie genetika metabolismus MeSH
- nestabilita genomu MeSH
- poškození DNA MeSH
- proteinové domény MeSH
- proteiny buněčného cyklu MeSH
- regulace genové exprese u hub * MeSH
- rekombinantní proteiny chemie genetika metabolismus MeSH
- replikace DNA MeSH
- Saccharomyces cerevisiae - proteiny chemie genetika metabolismus MeSH
- Saccharomyces cerevisiae genetika metabolismus MeSH
- vazba proteinů MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- DNA fungální MeSH
- DNA vazebné proteiny MeSH
- endonukleasy MeSH
- Esc2 protein, S cerevisiae MeSH Prohlížeč
- jaderné proteiny MeSH
- křížová struktura DNA MeSH
- malé modifikační proteiny související s ubikvitinem MeSH
- MUS81 protein, S cerevisiae MeSH Prohlížeč
- proteiny buněčného cyklu MeSH
- rekombinantní proteiny MeSH
- Saccharomyces cerevisiae - proteiny MeSH
UBL5 is an atypical ubiquitin-like protein, whose function in metazoans remains largely unexplored. We show that UBL5 is required for sister chromatid cohesion maintenance in human cells. UBL5 primarily associates with spliceosomal proteins, and UBL5 depletion decreases pre-mRNA splicing efficiency, leading to globally enhanced intron retention. Defective sister chromatid cohesion is a general consequence of dysfunctional pre-mRNA splicing, resulting from the selective downregulation of the cohesion protection factor Sororin. As the UBL5 yeast orthologue, Hub1, also promotes spliceosome functions, our results show that UBL5 plays an evolutionary conserved role in pre-mRNA splicing, the integrity of which is essential for the fidelity of chromosome segregation.
- Klíčová slova
- UBL5, pre‐mRNA splicing, sister chromatid cohesion, sororin, ubiquitin‐like protein,
- MeSH
- adaptorové proteiny signální transdukční genetika MeSH
- chromatidy genetika MeSH
- HeLa buňky MeSH
- lidé MeSH
- ligasy genetika MeSH
- mitóza genetika MeSH
- oční proteiny genetika metabolismus MeSH
- prekurzory RNA genetika MeSH
- proteiny buněčného cyklu genetika MeSH
- regulace genové exprese MeSH
- Saccharomyces cerevisiae - proteiny genetika MeSH
- segregace chromozomů genetika MeSH
- sestřih RNA genetika MeSH
- spliceozomy genetika MeSH
- ubikvitiny genetika metabolismus MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- adaptorové proteiny signální transdukční MeSH
- CDCA5 protein, human MeSH Prohlížeč
- HUB1 protein, S cerevisiae MeSH Prohlížeč
- ligasy MeSH
- oční proteiny MeSH
- prekurzory RNA MeSH
- proteiny buněčného cyklu MeSH
- Saccharomyces cerevisiae - proteiny MeSH
- ubikvitiny MeSH
- UBL5 protein, human MeSH Prohlížeč
