Crossovers Research Articles

MutS homologue 4 and MutS homologue 5 Maintain the Obligate Crossover in Wheat Despite Stepwise Gene Loss following Polyploidization.

Crossovers (COs) ensure accurate chromosome segregation during meiosis while creating novel allelic combinations. Here, we show that allotetraploid (AABB) durum wheat (Triticum turgidum ssp. durum) utilizes two pathways of meiotic recombination. The class I pathway requires MSH4 and MSH5 (MutSγ) to maintain the obligate CO/chiasma and accounts for ∼85% of meiotic COs, whereas the residual ∼15% are consistent with the class II CO pathway. Class I and class II chiasmata are skewed toward the chromosome ends, but class II chiasmata are significantly more distal than class I chiasmata. Chiasma distribution does not reflect the abundance of double-strand breaks, detected by proxy as RAD51 foci at leptotene, but only ∼2.3% of these sites mature into chiasmata. MutSγ maintains the obligate chiasma despite a 5.4-kb deletion in MSH5B rendering it nonfunctional, which occurred early in the evolution of tetraploid wheat and was then domesticated into hexaploid (AABBDD) common wheat (Triticum aestivum), as well as an 8-kb deletion in MSH4D in hexaploid wheat, predicted to create a nonfunctional pseudogene. Stepwise loss of MSH5B and MSH4D following hybridization and whole-genome duplication may have occurred due to gene redundancy (as functional copies of MSH5A, MSH4A, and MSH4B are still present in the tetraploid and MSH5A, MSH5D, MSH4A, and MSH4B are present in the hexaploid) or as an adaptation to modulate recombination in allopolyploid wheat.

Boundaries as Crossovers: The Shoreline as a Digressive Site in Ramkumar Mukhopadhyay’s Dhanapatir Sinhalyatra (2010)

Boundaries as Crossovers: The Shoreline as a Digressive Site in Ramkumar Mukhopadhyay’s Dhanapatir Sinhalyatra (2010)

Levels of Heterochiasmy During Arabidopsis Development as Reported by Fluorescent Tagged Lines.

Crossing over, the exchange of DNA between the chromosomes during meiosis, contributes significantly to genetic variation. The rate of crossovers (CO) varies depending upon the taxon, population, age, external conditions, and also, sometimes, between the sexes, a phenomenon called heterochiasmy. In the model plant Arabidopsis thaliana, the male rate of all crossover events (mCO) is typically nearly double the female rate (fCO). A previous, PCR-based genotyping study has reported that the disparity decreases with increasing parental age, because fCO rises while mCO remains stable. We revisited this topic using a fluorescent tagged lines approach to examine how heterochiasmy responded to parental age in eight genomic intervals distributed across the organism’s five chromosomes. We determined recombination frequency for, on average, more than 2000 seeds, for each interval, for each of four age groups, to estimate sex-specific CO rates. mCO did not change with age, as reported previously, but, here, fCO did not rise, and thus the levels of heterochiasmy were unchanged. We can see no methodological reason to doubt that our results reflect the underlying biology of the accessions we studied. The lack of response to age could perhaps be due to previously reported variation in CO rate among accessions of Arabidopsis.

Maintenance of meiotic crossover against reduced double-strand break formation in fission yeast lacking histone H2A.Z.

Meiotic crossover (CO) recombination initiates from programmed DNA double-strand breaks (DSBs) around hotspots, and results in reciprocal exchange of chromosome segments between homologous chromosomes (homologs). COs are crucial for most sexually-reproducing organisms because they promote accurate chromosome segregation and create genetic diversity. Therefore, faithful accomplishment of CO formation is ensured in many ways, but the bases of the regulation are not fully understood. Our previous study using fission yeast has revealed that mutants lacking the conserved histone H2A.Z are defective in DSB formation but maintain CO frequency at three loci tested. Here, we tested five additional sites to show that mutants lacking H2A.Z exhibit normal and increased CO frequency at two and three loci, respectively. Examining one of the CO-increased intervals in the mutant revealed that the CO upregulation is mediated at least partly at a recombination intermediate level. In addition, our genetic as well as genome-wide analyses implied a possibility that, even without H2A.Z, COs are maintained by weak and non-hotspot DSBs, which are processed preferentially as CO. These observations provide clues to further our understanding on CO control.

Theoretical and experimental results of optically pumped sodium atoms

Optical pumping is a process that produces a nonthermal Zeeman sublevel population distribution. It plays an important role in alkali-metal magnetometers for two uses, constructing the sub-Doppler features to lock the laser frequency and providing the spin-polarized atoms to precess around the magnetic field. To comprehensively study the properties of sodium (Na) magnetometer, we present the detailed theoretical analysis of the saturated absorption spectroscopy (SAS) and the magneto-optical resonance signal in sodium D2 line. Accordingly, we have implemented two experimental schemes, the counter propagating pump-probe SAS of thermal Na vapor and the remote sensing Bell-Bloom magnetometry based on the Larmor precession frequency. In the first experiment, sub-Doppler features of D2 consist of two velocity selective optical pumping (VSOP) resonances located at the D2a and D2b transitions and a crossover (CO) resonance located between the VSOP resonances are observed. In the second experiment, an estimated intrinsic magnetometric sensitivity of δBint=286 pT in a 1 Hz bandwidth, is achieved by demodulating the recorded fluorescence signal of the resultant magneto-optical resonance near the 300 kHz Larmor precession frequency. Both kinds of experimental results are in good agreement with our theoretical calculations.

Influence of energy drinks on acute hemodynamic parameters in young healthy adults: a randomized double-blind placebo-controlled crossover pilot study

Influence of energy drinks on acute hemodynamic parameters in young healthy adults: a randomized double-blind placebo-controlled crossover pilot study

Crossover Position Drives Chromosome Remodeling for Accurate Meiotic Chromosome Segregation.

Interhomolog crossovers (COs) are a prerequisite for achieving accurate chromosome segregation during meiosis [1, 2]. COs are not randomly positioned, occurring at distinct genomic intervals during meiosis in all species examined [3-10]. The role of CO position as a major determinant of accurate chromosome segregation has not been previously directly analyzed in a metazoan. Here, we use spo-11 mutants, which lack endogenous DNA double-strand breaks (DSBs), to induce a single DSB by Mos1 transposon excision at defined chromosomal locations in the C.elegans germline and show that the position of the resulting CO directly affects the formation of distinct chromosome subdomains during meiotic chromosome remodeling. CO formation in the typically CO-deprived center region of autosomes leads to premature loss of sister chromatid cohesion and chromosome missegregation, whereas COs at an off-centered position, as in wild type, can result in normal remodeling and accurate segregation. Ionizing radiation (IR)-induced DSBs lead to the same outcomes, and modeling of IR dose-response reveals that the CO-unfavorable center region encompasses up to 6% of the total chromosome length. DSBs proximal to telomeres rarely form COs, likely because of formation of unstable recombination intermediates that cannot be sustained as chiasmata until late prophase. Our work supports a model in which regulation of CO position early in meiotic prophase is required for proper designation of chromosome subdomains and normal chromosome remodeling in late meiotic prophase I, resulting in accurate chromosome segregation and providing a mechanism to prevent aneuploid gamete formation.

Refined spatial temporal epigenomic profiling reveals intrinsic connection between PRDM9-mediated H3K4me3 and the fate of double-stranded breaks

Meiotic recombination is initiated by the formation of double-strand breaks (DSBs), which are repaired as either crossovers (COs) or noncrossovers (NCOs). In most mammals, PRDM9-mediated H3K4me3 controls the nonrandom distribution of DSBs; however, both the timing and mechanism of DSB fate control remain largely undetermined. Here, we generated comprehensive epigenomic profiles of synchronized mouse spermatogenic cells during meiotic prophase I, revealing spatiotemporal and functional relationships between epigenetic factors and meiotic recombination. We find that PRDM9-mediated H3K4me3 at DSB hotspots, coinciding with H3K27ac and H3K36me3, is intimately connected with the fate of the DSB. Our data suggest that the fate decision is likely made at the time of DSB formation: earlier formed DSBs occupy more open chromatins and are much more competent to proceed to a CO fate. Our work highlights an intrinsic connection between PRDM9-mediated H3K4me3 and the fate decision of DSBs, and provides new insight into the control of CO homeostasis.

Crossovers: Food & Fashion and the Impact of Science

Crossovers: <i>Food &amp; Fashion and the Impact of Science</i>

Targeted Conditioning with Anti-CD45 Iodine (131I) Apamistamab [Iomab-B] Leads to High Rates of Allogeneic Transplantation and Successful Engraftment in Older Patients with Active, Relapsed or Refractory (rel/ref) AML after Failure of Chemotherapy and Targeted Agents: Preliminary Midpoint Results from the Prospective, Randomized Phase 3 Sierra Trial

<h3>Background</h3> Patients with rel/ref AML have very few options, despite novel targeted therapies (e.g. venetoclax, IDH inhibitors), other than allogeneic hematopoietic cell transplantation (HCT) to achieve a durable CR. In addition, patients ≥55 years of age cannot tolerate multiple cycles of intensive therapy trying to achieve a CR prior to transplant. Older patients are also unable to tolerate more intense myeloablative conditioning. The SIERRA trial is a prospective, randomized, phase 3 trial addressing the unmet need to improve access of older patients with active, rel/ref AML to HCT, the only potentially curative therapy available to them. <h3>Methods</h3> Patients are randomized (1:1) to receive Iomab-B (day-12) followed by FLU/TBI and HCT, or to conventional care (CC). CC patients may receive investigator's choice of salvage therapy, including newly approved targeted agents and may proceed to standard HCT if they achieve CR. If patients do not achieve CR, the study allows cross-over (CO) to Iomab-B/HCT. <h3>Results</h3> Preliminary data are available from 75 (50%) patients (Table 1). Patients (median age 64) were heavily pretreated with 85% failing ≥2 induction therapies and 33% failing targeted therapies. All patients transplanted after Iomab-B engrafted. After randomization, 82% (31/38) patients in the CC arm failed salvage therapy, despite 32% (12/38) receiving targeted therapy. 73% (8/11) of the patients receiving venetoclax with HMA or LDAC did not achieve remission. Of the 31 patients, 9 were not CO transplant candidates. Of the 22 patients that crossed over for transplant, majority (91%, N=20) were able to receive Iomab-B/HCT, despite a median of 35% BM blasts. The most common reason preventing CO to transplant was disease progression. CC patients showed increased incidence of Grade 3 febrile neutropenia, compared to Iomab-B patients prior to CO or HCT (34% vs 8%). Iomab-B administration was generally well-tolerated with 1 Grade 3 and no Grade 4, infusion reaction. There were no Iomab-B-related deaths and 100-day non-relapse TRM was 3% on the Iomab-B arm (Table 1). <h3>Conclusion</h3> Despite advanced age, active disease and heavily pre-treated patients, 100% (31/31) of all patients in the Iomab-B arm who received treatment with Iomab-B were able to undergo HCT and successfully engrafted. In comparison, only 18% (7/38) of the patients on the CC arm achieved remission and underwent conventional HCT despite a high percentage receiving recently approved agents and targeted therapies. Overall, including patients crossing over to receive Iomab-B/HCT after failure of salvage therapy in the CC arm, 68% (51/75) of all patients enrolled in the trial underwent HCT after Iomab-B. These preliminary results represent significant improvements in the current rates of transplantation in this patient population. This SIERRA trial is currently enrolling (www.sierratrial.com or clinicaltrials.gov NCT02665065).

Meiotic recombination profiling of interspecific hybrid F1 tomato pollen by linked read sequencing.

Genome wide screening of pooled pollen samples from a single interspecific F1 hybrid obtained from a cross between tomato, Solanum lycopersicum and its wild relative, Solanum pimpinellifolium using linked read sequencing of the haploid nuclei, allowed profiling of the crossover (CO) and gene conversion (GC) landscape. We observed a striking overlap between cold regions of CO in the male gametes and our previously established F6 recombinant inbred lines (RILs) population. COs were overrepresented in non-coding regions in the gene promoter and 5'UTR regions of genes. Poly-A/T and AT rich motifs were found enriched in 1kb promoter regions flanking the CO sites. Non-crossover associated allelic and ectopic GCs were detected in most chromosomes, confirming that besides CO, GC represents also a source for genetic diversity and genome plasticity in tomato. Furthermore, we identified processed break junctions pointing at the involvement of both homology directed and non-homology directed repair pathways, suggesting a recombination machinery in tomato that is more complex than currently anticipated.

Counting on Crossovers: Controlled Recombination for Plant Breeding.

Crossovers (COs), that drive genetic exchange between homologous chromosomes, are strongly biased toward subtelomeric regions in plant species. Manipulating the rate and positions of COs to increase the genetic variation accessible to breeders is a longstanding goal. Use of genome editing reagents that induce double-stranded breaks (DSBs) or modify the epigenome at desired sites of recombination, and manipulation of CO factors, are increasingly applicable approaches for achieving this goal. These strategies for 'controlled recombination' have potential to reduce the time and expense associated with traditional breeding, reveal currently inaccessible genetic diversity, and increase control over the inheritance of preferred haplotypes. Considerable challenges to address include translating knowledge from models to crop species and determining the best stages of the breeding cycle at which to control recombination.

Environmentally-relevant exposure to diethylhexyl phthalate (DEHP) alters regulation of double-strand break formation and crossover designation leading to germline dysfunction in Caenorhabditis elegans

Exposure to diethylhexyl phthalate (DEHP), the most abundant plasticizer used in the production of polyvinyl-containing plastics, has been associated to adverse reproductive health outcomes in both males and females. While the effects of DEHP on reproductive health have been widely investigated, the molecular mechanisms by which exposure to environmentally-relevant levels of DEHP and its metabolites impact the female germline in the context of a multicellular organism have remained elusive. Using the Caenorhabditis elegans germline as a model for studying reprotoxicity, we show that exposure to environmentally-relevant levels of DEHP and its metabolites results in increased meiotic double-strand breaks (DSBs), altered DSB repair progression, activation of p53/CEP-1-dependent germ cell apoptosis, defects in chromosome remodeling at late prophase I, aberrant chromosome morphology in diakinesis oocytes, increased chromosome non-disjunction and defects during early embryogenesis. Exposure to DEHP results in a subset of nuclei held in a DSB permissive state in mid to late pachytene that exhibit defects in crossover (CO) designation/formation. In addition, these nuclei show reduced Polo-like kinase-1/2 (PLK-1/2)-dependent phosphorylation of SYP-4, a synaptonemal complex (SC) protein. Moreover, DEHP exposure leads to germline-specific change in the expression of prmt-5, which encodes for an arginine methyltransferase, and both increased SC length and altered CO designation levels on the X chromosome. Taken together, our data suggest a model by which impairment of a PLK-1/2-dependent negative feedback loop set in place to shut down meiotic DSBs, together with alterations in chromosome structure, contribute to the formation of an excess number of DSBs and altered CO designation levels, leading to genomic instability.

Distinct Functions in Regulation of Meiotic Crossovers for DNA Damage Response Clamp Loader Rad24(Rad17) and Mec1(ATR) Kinase.

The number and distribution of meiotic crossovers (COs) are highly regulated, reflecting the requirement for COs during the first round of meiotic chromosome segregation. CO control includes CO assurance and CO interference, which promote at least one CO per chromosome bivalent and evenly-spaced COs, respectively. Previous studies revealed a role for the DNA damage response (DDR) clamp and the clamp loader in CO formation by promoting interfering COs and interhomolog recombination, and also by suppressing ectopic recombination. In this study, we use classical tetrad analysis of Saccharomyces cerevisiae to show that a mutant defective in RAD24, which encodes the DDR clamp loader (RAD17 in other organisms), displayed reduced CO frequencies on two shorter chromosomes (III and V), but not on a long chromosome (chromosome VII). The residual COs in the rad24 mutant do not show interference. In contrast to rad24, mutants defective in the ATR kinase homolog Mec1, including a mec1 null and a mec1 kinase-dead mutant, show slight or few defects in CO frequency. On the other hand, mec1 COs show defects in interference, similar to the rad24 mutant. Our results support a model in which the DDR clamp and clamp-loader proteins promote interfering COs by recruiting pro-CO Zip, Mer, and Msh proteins to recombination sites, while the Mec1 kinase regulates CO distribution by a distinct mechanism. Moreover, CO formation and its control are implemented in a chromosome-specific manner, which may reflect a role for chromosome size in regulation.

Re-Induction and Targeted Conditioning with Anti-CD45 Iodine (131I) Apamistamab [Iomab-B] Leads to High Rates of Transplantation and Successful Engraftment in Older Patients with Active, Relapsed or Refractory (rel/ref) AML after Failure of Chemotherapy and Targeted Agents: Preliminary Midpoint Results from the Prospective, Randomized Phase 3 Sierra Trial

Re-Induction and Targeted Conditioning with Anti-CD45 Iodine (131I) Apamistamab [Iomab-B] Leads to High Rates of Transplantation and Successful Engraftment in Older Patients with Active, Relapsed or Refractory (rel/ref) AML after Failure of Chemotherapy and Targeted Agents: Preliminary Midpoint Results from the Prospective, Randomized Phase 3 Sierra Trial

An Ultra High-Density Arabidopsis thaliana Crossover Map That Refines the Influences of Structural Variation and Epigenetic Features.

Many environmental, genetic, and epigenetic factors are known to affect the frequency and positioning of meiotic crossovers (COs). Suppression of COs by large, cytologically visible inversions and translocations has long been recognized, but relatively little is known about how smaller structural variants (SVs) affect COs. To examine fine-scale determinants of the CO landscape, including SVs, we used a rapid, cost-effective method for high-throughput sequencing to generate a precise map of >17,000 COs between the Col-0 and Ler-0 accessions of Arabidopsis thaliana COs were generally suppressed in regions with SVs, but this effect did not depend on the size of the variant region, and was only marginally affected by the variant type. CO suppression did not extend far beyond the SV borders and CO rates were slightly elevated in the flanking regions. Disease resistance gene clusters, which often exist as SVs, exhibited high CO rates at some loci, but there was a tendency toward depressed CO rates at loci where large structural differences exist between the two parents. Our high-density map also revealed in fine detail how CO positioning relates to genetic (DNA motifs) and epigenetic (chromatin structure) features of the genome. We conclude that suppression of COs occurs over a narrow region spanning large- and small-scale SVs, representing an influence on the CO landscape in addition to sequence and epigenetic variation along chromosomes.

Vitamin E absorption and kinetics in healthy women, as modulated by food and by fat, studied using 2 deuterium-labeled α-tocopherols in a 3-phase crossover design

Determining the human vitamin E [α-tocopherol (α-T)] requirement is difficult, and novel approaches to assess α-T absorption and trafficking are needed. We hypothesized that the dual-isotope technique, using 2 deuterium-labeled [intravenous (IV) d6- and oral d3-] α-T, would be effective in determining α-T fractional absorption. Further, defined liquid meal (DLM) fat or fasting would modulate α-T fractional absorption and lipoprotein transport. A 3-phase cr ossover design was used. At 0 h, participants received IV d6-α-T and consumed d3-α-T with a 600-kcal DLM (40% or 0% fat) followed by controlled meals or by the 0% fat DLM, a 12-h fast, and then controlled meals. Blood samples and fecal samples were collected at intervals and analyzed by LC-MS. Pharmacokinetic parameters were calculated from plasma tracer concentrations and enrichments. Fractional absorption was calculated from d3- to d6-α-T areas under the curve, from a novel mathematical model, and from the balance method (oral d3-α-T minus fecal d3-α-T excreted). Estimated α-T fractional absorption during the 40% fat intervention was 55%±3% (mean±SEM; n=10), which was 9% less than during the 0% fat intervention (64%±3%, n=10; P<0.02). Fasting had no apparent effect (56%±3%, n=7), except it slowed plasma oral d3-α-T appearance. Both balance data and model outcomes confirmed that the DLM fat did not potentiate d3-α-T absorption. During the IV emulsion clearance, HDL rapidly acquired d6-α-T (21±2 nmol/L plasma per minute). During the first 8 h postdosing, triglyceride-rich lipoproteins (TRLs) were preferentially d3-α-T enriched relative to LDL or HDL, showing the TRL precursor role. Quantitatively, α-T absorption is not limited by fat absence or by fasting. However, α-T leaves the intestine by a process that is prolonged during fasting and potentiated by eating, suggesting that α-T absorption is highly dependent on chylomicron assembly processes. This trial was registered at clinicaltrials.gov as NCT00862433.

Ku complex suppresses recombination in the absence of MRX activity during budding yeast meiosis

During meiosis, programmed double-strand breaks (DSBs) are repaired via recombination pathways that are required for faithful chromosomal segregation and genetic diversity. In meiotic progression, the non-homologous end joining (NHEJ) pathway is suppressed and instead meiotic recombination initiated by nucleolytic resection of DSB ends is the major pathway employed. This requires diverse recombinase proteins and regulatory factors involved in the formation of crossovers (COs) and non-crossovers (NCOs). In mitosis, spontaneous DSBs occurring at the G1 phase are predominantly repaired via NHEJ, mediating the joining of DNA ends. The Ku complex binds to these DSB ends, inhibiting additional DSB resection and mediating end joining with Dnl4, Lif1, and Nej1, which join the Ku complex and DSB ends. Here, we report the role of the Ku complex in DSB repair using a physical analysis of recombination in Saccharomyces cerevisiae during meiosis. We found that the Ku complex is not essential for meiotic progression, DSB formation, joint molecule formation, or CO/NCO formation during normal meiosis. Surprisingly, in the absence of the Ku complex and functional Mre11-Rad50-Xrs2 (MRX) complex, a large portion of meiotic DSBs was repaired via the recombination pathway to form COs and NCOs. Our data suggested that Ku complex prevents meiotic recombination in the elimination of MRX activity.

교차 충성도의 변화: O2O 시대의 쇼핑 메카니즘의 진화

교차 충성도의 변화: O2O 시대의 쇼핑 메카니즘의 진화

Meiotic crossovers characterized by haplotype-specific chromosome painting in maize

Meiotic crossovers (COs) play a critical role in generating genetic variation and maintaining faithful segregation of homologous chromosomes during meiosis. We develop a haplotype-specific fluorescence in situ hybridization (FISH) technique that allows visualization of COs directly on metaphase chromosomes. Oligonucleotides (oligos) specific to chromosome 10 of maize inbreds B73 and Mo17, respectively, are synthesized and labeled as FISH probes. The parental and recombinant chromosome 10 in B73 x Mo17 F1 hybrids and F2 progenies can be unambiguously identified by haplotype-specific FISH. Analysis of 58 F2 plants reveals lack of COs in the entire proximal half of chromosome 10. However, we detect COs located in regions very close to the centromere in recombinant inbred lines from an intermated B73 x Mo17 population, suggesting effective accumulation of COs in recombination-suppressed chromosomal regions through intermating and the potential to generate favorable allelic combinations of genes residing in these regions.