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Science Advances Jul 2017The human genetic material is packaged into 46 chromosomes. The structure of chromosomes is known at the lowest level, where the DNA chain is wrapped around a core of...
The human genetic material is packaged into 46 chromosomes. The structure of chromosomes is known at the lowest level, where the DNA chain is wrapped around a core of eight histone proteins to form nucleosomes. Around a million of these nucleosomes, each about 11 nm in diameter and 6 nm in thickness, are wrapped up into the complex organelle of the chromosome, whose structure is mostly known at the level of visible light microscopy to form a characteristic cross shape in metaphase. However, the higher-order structure of human chromosomes, between a few tens and hundreds of nanometers, has not been well understood. We show a three-dimensional (3D) image of a human prophase nucleus obtained by serial block-face scanning electron microscopy, with 36 of the complete set of 46 chromosomes captured within it. The acquired image allows us to extract quantitative 3D structural information about the nucleus and the preserved, intact individual chromosomes within it, including their positioning and full spatial morphology at a resolution of around 50 nm in three dimensions. The chromosome positions were found, at least partially, to follow the pattern of chromosome territories previously observed only in interphase. The 3D conformation shows parallel, planar alignment of the chromatids, whose occupied volumes are almost fully accounted for by the DNA and known chromosomal proteins. We also propose a potential new method of identifying human chromosomes in three dimensions, on the basis of the measurements of their 3D morphology.
Topics: Cell Line; Cell Nucleus; Chromosomes, Human; Humans; Imaging, Three-Dimensional; Prophase
PubMed: 28776025
DOI: 10.1126/sciadv.1602231 -
PLoS Genetics 2013Cohesin subunit SMC1β is specific and essential for meiosis. Previous studies showed functions of SMC1β in determining the axis-loop structure of synaptonemal...
Cohesin subunit SMC1β is specific and essential for meiosis. Previous studies showed functions of SMC1β in determining the axis-loop structure of synaptonemal complexes (SCs), in providing sister chromatid cohesion (SCC) in metaphase I and thereafter, in protecting telomere structure, and in synapsis. However, several central questions remained unanswered and concern roles of SMC1β in SCC and synapsis and processes related to these two processes. Here we show that SMC1β substantially supports prophase I SCC at centromeres but not along chromosome arms. Arm cohesion and some of centromeric cohesion in prophase I are provided by non-phosphorylated SMC1α. Besides supporting synapsis of autosomes, SMC1β is also required for synapsis and silencing of sex chromosomes. In absence of SMC1β, the silencing factor γH2AX remains associated with asynapsed autosomes and fails to localize to sex chromosomes. Microarray expression studies revealed up-regulated sex chromosome genes and many down-regulated autosomal genes. SMC1β is further required for non-homologous chromosome associations observed in absence of SPO11 and thus of programmed double-strand breaks. These breaks are properly generated in Smc1β⁻/⁻ spermatocytes, but their repair is delayed on asynapsed chromosomes. SMC1α alone cannot support non-homologous associations. Together with previous knowledge, three main functions of SMC1β have emerged, which have multiple consequences for spermatocyte biology: generation of the loop-axis architecture of SCs, homologous and non-homologous synapsis, and SCC starting in early prophase I.
Topics: Animals; Cell Cycle Proteins; Centromere; Chromosome Pairing; Chromosome Segregation; Endodeoxyribonucleases; Male; Meiosis; Meiotic Prophase I; Mice; Spermatocytes; Synaptonemal Complex; Telomere
PubMed: 24385917
DOI: 10.1371/journal.pgen.1003985 -
Fertility and Sterility May 1994To determine the potential for in vitro maturation, fertilization, and cleavage after cryopreservation of immature, prophase I human oocytes. (Clinical Trial)
Clinical Trial Comparative Study Randomized Controlled Trial
OBJECTIVE
To determine the potential for in vitro maturation, fertilization, and cleavage after cryopreservation of immature, prophase I human oocytes.
DESIGN
Immature oocytes obtained in excess of the number required by the patient were randomized and cryopreserved at the prophase I stage or cultured as control. After thawing and maturation in vitro, test and control oocytes were inseminated with husband's sperm and evaluated for fertilization and cleavage in vitro.
SETTING
In vitro fertilization program.
PATIENTS
Consenting patients undergoing controlled ovarian hyperstimulation for the purposes of IVF.
MAIN OUTCOME MEASURES
Rates of maturation to metaphase II, fertilization, and cleavage were compared between control and cryopreserved oocytes.
RESULTS
Upon thaw, 58.5% (72/123) of prophase I oocytes were viable. Control oocytes demonstrated a 74.8% (98/131) maturation rate to metaphase II, a 56.5% (52/92) fertilization rate, and an 11.5% (6/52) blastocyst rate. Cryopreserved oocytes showed a 83.3% (60/72) rate of maturation, a 57.7% (30/52) fertilization rate, and a 3.3% (1/30) blastocyst rate. No significant differences were noted between any of these parameters.
CONCLUSIONS
These results demonstrate that prophase I oocytes from stimulated IVF cycles are able to survive cryopreservation and resume meiosis to achieve full nuclear maturation post-thaw. In addition, cryopreserved oocytes retain the same capacity for fertilization and development as control oocytes.
Topics: Adult; Cryopreservation; Female; Fertility; Fertilization; Fertilization in Vitro; Humans; In Vitro Techniques; Metaphase; Oocytes; Ovary; Ovulation Induction; Prophase; Tissue Preservation
PubMed: 8174727
DOI: 10.1016/s0015-0282(16)56702-8 -
PLoS Genetics Mar 2024During meiosis, genetic recombination is initiated by the formation of many DNA double-strand breaks (DSBs) catalysed by the evolutionarily conserved topoisomerase-like...
During meiosis, genetic recombination is initiated by the formation of many DNA double-strand breaks (DSBs) catalysed by the evolutionarily conserved topoisomerase-like enzyme, Spo11, in preferred genomic sites known as hotspots. DSB formation activates the Tel1/ATM DNA damage responsive (DDR) kinase, locally inhibiting Spo11 activity in adjacent hotspots via a process known as DSB interference. Intriguingly, in S. cerevisiae, over short genomic distances (<15 kb), Spo11 activity displays characteristics of concerted activity or clustering, wherein the frequency of DSB formation in adjacent hotspots is greater than expected by chance. We have proposed that clustering is caused by a limited number of sub-chromosomal domains becoming primed for DSB formation. Here, we provide evidence that DSB clustering is abolished when meiotic prophase timing is extended via deletion of the NDT80 transcription factor. We propose that extension of meiotic prophase enables most cells, and therefore most chromosomal domains within them, to reach an equilibrium state of similar Spo11-DSB potential, reducing the impact that priming has on estimates of coincident DSB formation. Consistent with this view, when Tel1 is absent but Ndt80 is present and thus cells are able to rapidly exit meiotic prophase, genome-wide maps of Spo11-DSB formation are skewed towards pericentromeric regions and regions that load pro-DSB factors early-revealing regions of preferential priming-but this effect is abolished when NDT80 is deleted. Our work highlights how the stochastic nature of Spo11-DSB formation in individual cells within the limited temporal window of meiotic prophase can cause localised DSB clustering-a phenomenon that is exacerbated in tel1Δ cells due to the dual roles that Tel1 has in DSB interference and meiotic prophase checkpoint control.
Topics: DNA; DNA Breaks, Double-Stranded; DNA-Binding Proteins; Endodeoxyribonucleases; Intracellular Signaling Peptides and Proteins; Meiosis; Prophase; Protein Serine-Threonine Kinases; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 38427688
DOI: 10.1371/journal.pgen.1011140 -
Cell Reports Nov 2021Synaptonemal complex (SC) assembly and homologous recombination, the most critical events during prophase I, are the prerequisite for faithful meiotic chromosome...
Synaptonemal complex (SC) assembly and homologous recombination, the most critical events during prophase I, are the prerequisite for faithful meiotic chromosome segregation. However, the underlying regulatory mechanism remains largely unknown. Here, we reveal that a functional RING finger E3 ubiquitin ligase, DESYNAPSIS1 (DSNP1), plays significant roles in SC assembly and homologous recombination during rice meiosis. In the dsnp1 mutant, homologous synapsis is discontinuous and aberrant SC-like polycomplexes occur independent of coaligned homologous chromosomes. Accompanying the decreased foci of HEI10, ZIP4, and MER3 on meiotic chromosomes, the number of crossovers (COs) decreases dramatically in dsnp1 meiocytes. Furthermore, the absence of central elements largely restores the localization of non-ZEP1 ZMM proteins and the number of COs in the dsnp1 background. Collectively, DSNP1 stabilizes the canonical tripartite SC structure along paired homologous chromosomes and further promotes the formation of COs.
Topics: Chromosome Pairing; Chromosomes, Plant; Crossing Over, Genetic; Gene Expression Regulation, Plant; Meiosis; Oryza; Plant Proteins; Recombination, Genetic; Synaptonemal Complex; Ubiquitin-Protein Ligases
PubMed: 34731625
DOI: 10.1016/j.celrep.2021.109941 -
Plant Signaling & Behavior 2015Correct positioning of the division plane is a prerequisite for plant morphogenesis. The preprophase band (PPB) is a key intracellular structure of division site...
Correct positioning of the division plane is a prerequisite for plant morphogenesis. The preprophase band (PPB) is a key intracellular structure of division site determination. PPB forms in G2 phase as a broad band of microtubules (MTs) that narrows in prophase and specializes few-micrometer-wide cortical belt region, named the cortical division zone (CDZ), in late prophase. The PPB comprises several molecules, some of which act as MT band organization and others remain in the CDZ marking the correct insertion of the cell plate in telophase. Ran GTPase-activating protein (RanGAP) is accumulated in the CDZ and forms a RanGAP band in prophase. However, little is known about when and how RanGAPs gather in the CDZ, and especially with regard to their relationships to MT band formation. Here, we examined the spatial and temporal distribution of RanGAPs and MTs in the preprophase of onion root tip cells using confocal laser scanning microscopy and showed that the RanGAP band appeared in mid-prophase as the width of MT band was reduced to nearly 7 µm. Treatments with cytoskeletal inhibitors for 15 min caused thinning or broadening of the MT band but had little effects on RanGAP band in mid-prophase and most of late prophase cells. Detailed image analyses of the spatial distribution of RanGAP band and MT band showed that the RanGAP band positioned slightly beneath the MT band in mid-prophase. These results raise a possibility that RanGAP behaves differently from MTs during their band formation.
Topics: Antibodies; Bridged Bicyclo Compounds, Heterocyclic; Dinitrobenzenes; GTPase-Activating Proteins; Meristem; Microtubules; Models, Biological; Onions; Plant Proteins; Prophase; Protein Transport; Spatio-Temporal Analysis; Sulfanilamides; Thiazolidines; Tubulin
PubMed: 26237087
DOI: 10.1080/15592324.2015.1060385 -
Philosophical Transactions of the Royal... Dec 2017Meiosis is unusual among cell divisions in shuffling genetic material by crossovers among homologous chromosomes and partitioning the genome into haploid gametes.... (Review)
Review
Meiosis is unusual among cell divisions in shuffling genetic material by crossovers among homologous chromosomes and partitioning the genome into haploid gametes. Crossovers are critical for chromosome segregation in most eukaryotes, but are also an important factor in evolution, as they generate novel genetic combinations. The molecular mechanisms that underpin meiotic recombination and chromosome segregation are well conserved across kingdoms, but are also sensitive to perturbation by environment, especially temperature. Even subtle shifts in temperature can alter the number and placement of crossovers, while at greater extremes, structural failures can occur in the linear axis and synaptonemal complex structures which are essential for recombination and chromosome segregation. Understanding the effects of temperature on these processes is important for its implications in evolution and breeding, especially in the context of global warming. In this review, we first summarize the process of meiotic recombination and its reliance on axis and synaptonemal complex structures, and then discuss effects of temperature on these processes and structures. We hypothesize that some consistent effects of temperature on recombination and meiotic thermotolerance may commonly be two sides of the same coin, driven by effects of temperature on the folding or interaction of key meiotic proteins.This article is part of the themed issue 'Evolutionary causes and consequences of recombination rate variation in sexual organisms'.
Topics: Global Warming; Meiosis; Recombination, Genetic; Synaptonemal Complex; Temperature; Thermotolerance
PubMed: 29109229
DOI: 10.1098/rstb.2016.0470 -
Journal of Experimental Botany Apr 2021Meiosis generates genetic variation through homologous recombination (HR) that is harnessed during breeding. HR occurs in the context of meiotic chromosome axes and the...
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.
Topics: Brassica rapa; Chromosome Pairing; DNA-Binding Proteins; Homologous Recombination; Meiosis; Plant Breeding; Synaptonemal Complex
PubMed: 33502451
DOI: 10.1093/jxb/erab035 -
Molecular Plant Nov 2008In higher plants, the preprophase band (PPB) of microtubules (MTs) forecasts the cell division site prior to mitosis and specifies the organization of MTs into a bipolar...
In higher plants, the preprophase band (PPB) of microtubules (MTs) forecasts the cell division site prior to mitosis and specifies the organization of MTs into a bipolar prophase spindle surrounding the nucleus. However, the mechanisms governing this PPB-dependent establishment of bipolarity are unclear. Here, we present evidence from live cell imaging studies that suggest a role for the MTs bridging the PPB and the prophase nucleus in mediating this function. Results from drug treatments, along with genetic evidence from null kinesin plants, suggest that these MTs contribute to the bipolarity, orientation, and position of the prophase spindle. Specifically, the absence of these bridge MTs is associated with lack of bipolarity, while non-uniform distributions of bridge MTs correlate with prophase spindle migration, deformation, and enhanced bipolarity toward the region of highest bridge MT density. This behavior does not require actomyosin-based forces, and is enhanced by suppressing MT dynamics with taxol. These observations occur during late prophase, and are coincident with the gradual closing of annular spindle poles. Based on these data, we describe a hypothetical mechanism for bridge MT-dependent organization of prophase spindles.
Topics: Actins; Cell Nucleus; Microtubules; Models, Biological; Paclitaxel; Prophase; Spindle Apparatus; Nicotiana
PubMed: 19825595
DOI: 10.1093/mp/ssn054 -
Communications Biology Jul 2023The nucleus plays a central role in several key cellular processes, including chromosome organisation, DNA replication and gene transcription. Recent work suggests an...
The nucleus plays a central role in several key cellular processes, including chromosome organisation, DNA replication and gene transcription. Recent work suggests an association between nuclear mechanics and cell-cycle progression, but many aspects of this connection remain unexplored. Here, by monitoring nuclear shape fluctuations at different cell cycle stages, we uncover increasing inward fluctuations in late G2 and in early prophase, which are initially transient, but develop into instabilities when approaching the nuclear-envelope breakdown. We demonstrate that such deformations correlate with chromatin condensation by perturbing both the chromatin and the cytoskeletal structures. We propose that the contrasting forces between an extensile stress and centripetal pulling from chromatin condensation could mechanically link chromosome condensation with nuclear-envelope breakdown, two main nuclear processes occurring during mitosis.
Topics: Humans; Chromatin; Cell Nucleus; Mitosis; Prophase; Research Personnel
PubMed: 37438411
DOI: 10.1038/s42003-023-05074-9