Rec8 Cohesin-mediated Axis-loop chromatin architecture is required for meiotic recombination

Quantitative proteomics and phosphoproteomics profiling of meiotic divisions in the fission yeast Schizosaccharomyces pombe

In eukaryotes, chromosomal DNA is equally distributed to daughter cells during mitosis, whereas the number of chromosomes is halved during meiosis. Despite considerable progress in understanding the molecular mechanisms that regulate mitosis, there is currently a lack of complete understanding of the molecular mechanisms regulating meiosis. Here, we took advantage of the fission yeast Schizosaccharomyces pombe, for which highly synchronous meiosis can be induced, and performed quantitative proteomics and phosphoproteomics analyses to track changes in protein expression and phosphorylation during meiotic divisions. We compared the proteomes and phosphoproteomes of exponentially growing mitotic cells with cells harvested around meiosis I, or meiosis II in strains bearing either the temperature-sensitive pat1-114 allele or conditional ATP analog-sensitive pat1-as2 allele of the Pat1 kinase. Comparing pat1-114 with pat1-as2 also allowed us to investigate the impact of elevated temperature (25 °C versus 34 °C) on meiosis, an issue that sexually reproducing organisms face due to climate change. Using TMTpro 18plex labeling and phosphopeptide enrichment strategies, we performed quantification of a total of 4673 proteins and 7172 phosphosites in S. pombe. We found that the protein level of 2680 proteins and the rate of phosphorylation of 4005 phosphosites significantly changed during progression of S. pombe cells through meiosis. The proteins exhibiting changes in expression and phosphorylation during meiotic divisions were represented mainly by those involved in the meiotic cell cycle, meiotic recombination, meiotic nuclear division, meiosis I, centromere clustering, microtubule cytoskeleton organization, ascospore formation, organonitrogen compound biosynthetic process, carboxylic acid metabolic process, gene expression, and ncRNA processing, among others. In summary, our findings provide global overview of changes in the levels and phosphorylation of proteins during progression of S. pombe cells through meiosis at normal and elevated temperatures, laying the groundwork for further elucidation of the functions and importance of specific proteins and their phosphorylation in regulating meiotic divisions in this yeast.

Principles of chromosome organization for meiotic recombination

In meiotic cells, chromosomes are organized as chromatin loop arrays anchored to a protein axis. This organization is essential to regulate meiotic recombination, from DNA double-strand break (DSB) formation to their repair. In mammals, it is unknown how chromatin loops are organized along the genome and how proteins participating in DSB formation are tethered to the chromosome axes. Here, we identify three categories of axis-associated genomic sites: PRDM9 binding sites, where DSBs form; binding sites of the insulator protein CTCF; and H3K4me3-enriched sites. We demonstrate that PRDM9 promotes the recruitment of MEI4 and IHO1, two proteins essential for DSB formation. In turn, IHO1 anchors DSB sites to the axis components HORMAD1 and SYCP3. We discovered that IHO1, HORMAD1, and SYCP3 are associated at the DSB ends during DSB repair. Our results highlight how interactions of proteins with specific genomic elements shape the meiotic chromosome organization for recombination.

REC8 regulates neuroblastoma cell proliferation, migration, invasion, and angiogenesis via STAT3/VEGF signaling

BACKGROUND

Neuroblastoma, one of the most prevalent childhood cancers, is often treated with surgery, radiation, and chemotherapy. However, prognosis and survival are still dismal for children with neuroblastoma at high risk. Consequently, it is vital to identify new and effective treatment targets. As a component of the meiotic cohesion complex, REC8 is involved in a wide range of malignancies. The current work assessed the impact of REC8 knockdown on SH-SY5Y and SK-N-AS neuroblastoma cells and delved into the molecular mechanism behind this effect.

METHODS

Knockdown of REC8 using the small interfering (si) RNA technology, and the results were verified by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and western blot. The Cell Counting Kit-8 (CCK-8) was used to examine cell proliferation, while flow cytometry was used to examine cell cycle progression and apoptosis. Analyses of angiogenesis included tube formation experiments. Transwell tests were used to examine cell migration and invasion.

RESULTS

The data showed that downregulation of the REC8 led to a substantial decrease in cell proliferation by stopping the cell cycle in the G1 phase. REC8 knockdown significantly reduced neuroblastoma cell proliferation, migration, invasion, angiogenesis, induced cell cycle arrest, and enhanced apoptosis. We also discovered that repressing REC8 expression in neuroblastoma cell lines SH-SY5Y and SK-N-AS reduced their ability to activate the STAT3/VEGF signaling pathway.

CONCLUSIONS

Neuroblastoma therapy may benefit from targeting REC8 and its downstream targets.

Sevoflurane with Low Concentration Decrease DNA Methylation on Chronic Obstructive Pulmonary Disease (COPD)-Related Gene Promoter in COPD Rat

Chronic obstructive pulmonary disease (COPD) is a difficult-to-cure disease that mainly affects the respiratory system. Inhaled anesthetic drug such as sevoflurane plays a controversial role in COPD by different concentration, but the underlying epigenetic mechanism remains unclear. Here, we prepared lipopolysaccharide (LPS)-induced COPD rat model, and isolated Alveolar type II (ATII) cells. We mainly focused DNA methylation on the promoter of COPD-related genes including Sftpa1, Napsa, Ca2, Sfta2, Lamp3, Wif1, Pgc, and Etv5. We observed COPD rat treated by sevoflurane with low (0.5%) and high (2%) concentrations displayed an opposite DNA methylation pattern. These six genes' promoter were all hypomethylated by 0.5% sevoflurane whereas hypermethylated by 2% sevoflurane, accompanied with the opposite transcriptional activity. We further verified that the DNMT1 binding ability contributed to DNA methylation these six genes' promoter. Moreover, we also captured DNMT1 and identified REC8 meiotic recombination protein (REC8) as the specific binding protein only existed in ATII cells treated with 0.5% sevoflurane rather than 2% and control. The binding ability of REC8 on these target genes' promoter showed highly positive correlation with DNMT1. In summary, we uncovered a potential epigenetic role of sevoflurane with low concentration in ATII cells of COPD that may help us deeply understand the pathogenesis and treatment mechanism of inhaled anesthesia drugs in COPD via a dose-dependent manner.

Meiosis: Dances Between Homologs

The raison d'être of meiosis is shuffling of genetic information via Mendelian segregation and, within individual chromosomes, by DNA crossing-over. These outcomes are enabled by a complex cellular program in which interactions between homologous chromosomes play a central role. We first provide a background regarding the basic principles of this program. We then summarize the current understanding of the DNA events of recombination and of three processes that involve whole chromosomes: homolog pairing, crossover interference, and chiasma maturation. All of these processes are implemented by direct physical interaction of recombination complexes with underlying chromosome structures. Finally, we present convergent lines of evidence that the meiotic program may have evolved by coupling of this interaction to late-stage mitotic chromosome morphogenesis.

Cohesin mediates DNA loop extrusion and sister chromatid cohesion by distinct mechanisms

Cohesin connects CTCF-binding sites and other genomic loci in cis to form chromatin loops and replicated DNA molecules in trans to mediate sister chromatid cohesion. Whether cohesin uses distinct or related mechanisms to perform these functions is unknown. Here, we describe a cohesin hinge mutant that can extrude DNA into loops but is unable to mediate cohesion in human cells. Our results suggest that the latter defect arises during cohesion establishment. The observation that cohesin's cohesion and loop extrusion activities can be partially separated indicates that cohesin uses distinct mechanisms to perform these two functions. Unexpectedly, the same hinge mutant can also not be stopped by CTCF boundaries as well as wild-type cohesin. This suggests that cohesion establishment and cohesin's interaction with CTCF boundaries depend on related mechanisms and raises the possibility that both require transient hinge opening to entrap DNA inside the cohesin ring.

Chromosome architecture and homologous recombination in meiosis

Meiocytes organize higher-order chromosome structures comprising arrays of chromatin loops organized at their bases by linear axes. As meiotic prophase progresses, the axes of homologous chromosomes align and synapse along their lengths to form ladder-like structures called synaptonemal complexes (SCs). The entire process of meiotic recombination, from initiation via programmed DNA double-strand breaks (DSBs) to completion of DSB repair with crossover or non-crossover outcomes, occurs in the context of chromosome axes and SCs. These meiosis-specific chromosome structures provide specialized environments for the regulation of DSB formation and crossing over. In this review, we summarize insights into the importance of chromosome architecture in the regulation of meiotic recombination, focusing on cohesin-mediated axis formation, DSB regulation via tethered loop-axis complexes, inter-homolog template bias facilitated by axial proteins, and crossover regulation in the context of the SCs. We also discuss emerging evidence that the SUMO and the ubiquitin-proteasome system function in the organization of chromosome structure and regulation of meiotic recombination.

Transcriptional Specificity Analysis of Testis and Epididymis Tissues in Donkey

Donkeys, with high economic value for meat, skin and milk production, are important livestock. However, the current insights into reproduction of donkeys are far from enough. To obtain a deeper understanding, the differential expression analysis and weighted gene co-expression network analysis (WGCNA) of transcriptomic data of testicular and epididymis tissues in donkeys were performed. In the result, there were 4313 differentially expressed genes (DEGs) in the two tissues, including 2047 enriched in testicular tissue and 2266 in epididymis tissue. WGCNA identified 1081 hub genes associated with testis development and 6110 genes with epididymal development. Next, the tissue-specific genes were identified with the above two methods, and the gene ontology (GO) analysis revealed that the epididymal-specific genes were associated with gonad development. On the other hand, the testis-specific genes were involved in the formation of sperm flagella, meiosis period, ciliary assembly, ciliary movement, etc. In addition, we found that eca-Mir-711 and eca-Mir-143 likely participated in regulating the development of epididymal tissue. Meanwhile, eca-Mir-429, eca-Mir-761, eca-Mir-200a, eca-Mir-191 and eca-Mir-200b potentially played an important role in regulating the development of testicular tissue. In short, these results will contribute to functional studies of the male reproductive trait in donkeys.