CENP-A Regulates Chromosome Segregation during the First Meiosis of Mouse Oocytes

Proper chromosome separation in both mitosis and meiosis depends on the correct connection between kinetochores of chromosomes and spindle microtubules. Kinetochore dysfunction can lead to unequal distribution of chromosomes during cell division and result in aneuploidy, thus kinetochores are critical for faithful segregation of chromosomes. Centromere protein A(CENP-A) is an important component of the inner kinetochore plate. Multiple studies in mitosis have found that deficiencies in CENP-A could result in structural and functional changes of kinetochores, leading to abnormal chromosome segregation, aneuploidy and apoptosis in cells. Here we report the expression and function of CENP-A during mouse oocyte meiosis. Our study found that microinjection of CENP-A blocking antibody resulted in errors of homologous chromosome segregation and caused aneuploidy in eggs. Thus, our findings provide evidence that CENP-A is critical for the faithful chromosome segregation during mammalian oocyte meiosis.

Age-cumulative Effect of REC8 Reduction on Meiotic Chromosome Segregation Errors in Mice

Objective:This study aimed to explore the relationship between cohesin subunit REC8 reduction and meiosis chromosome segregation errors in the ovary.Methods:Rec8^(+/-)mice were generated using CRIPSR/Cas9 gene editing.The association between age and REC8 expression levels in the ovary was determined by Western blotting.Chromosome segregation errors were investigated by immunofluorescence imaging of superovulated oocytes.Wild-type andRec8^(+/-)female mice at 5,8,20,36,and 40 weeks were used to evaluate ovarian reserve by ovarian clearing and immunolabeling.Results:Ovary REC8 expression levels gradually decreased with age,while chromosome segregation errors increased with age.Segregation errors were more common inRec8^(+/-)mice,suggesting an association with REC8 expression.The ovarian reserve capacity decreased significantly with age.The ovarian reserve inRec8^(+/-)mice was inferior to that of age-matched wild-type mice,indicating important roles of age and REC8 levels in the ovarian reserve.Conclusions:REC8 reduction has an age-cumulative effect on meiotic chromosome segregation errors in mouse ovaries.Rec8 haploinsufficiency poses a major challenge in generating normal and reproductive oocytes in aging mice.

MreBCD-associated Cytoskeleton is Required for Proper Segregation of the Chromosomal Terminus during the Division Cycle of Escherichia Coli

Background：In prokaryotic organisms,the mechanism responsible for the accurate partition of newly replicated chromosomes into daughter cells is incompletely understood.Segregation of the replication terminus of the circular prokaryotic chromosome poses special problems that have not previously been addressed.The aim of this study was to investigate the roles of several protein components （MreB,MreC,and MreD） of the prokaryotic cytoskeleton for the faithful transmission of the chromosomal terminus into daughter cells.Methods：Strain LQ1 （mreB：：cat）,LQ2 （mreC：：cat）,and LQ3 （mreD：：cat） were constructed using the Red recombination system.LQ11/pLAU53,LQ12/pLAU53,LQ13/pLAU53,LQ14/pLAU53,and LQ15/pLAU53 strains were generated by Pltransduction of （tetO）240-Gm and （lacO）240-Km cassettes from strains IL2 and IL29.Fluorescence microscopy was performed to observe localization pattern of fluorescently-labeled origin and terminus foci in wild-type and mutant cells.SOS induction was monitored as gfp fluorescence from PsulA-gfp in log phase cells grown in Luria-Bertani medium at 37℃ by measurement of emission at 525 nm with excitation at 470 nm in a microplate fluorescence reader.Results：Mutational deletion of the mreB,mreC,or mreD genes was associated with selective loss of the terminus region in approximately 40％ of the cells within growing cultures.This was accompanied by significant induction of the SOS DNA damage response,suggesting that deletion of terminus sequences may have occurred by chromosomal cleavage,presumably caused by ingrowth of the division septum prior to segregation of the replicated terminal.Conclusions：These results imply a role for the MreBCD cytoskeleton in the resolution of the final products of terminus replication and/ or in the specific movement of newly replicated termini away from midcell prior to completion of septal ingrowth.This would identify a previously unrecognized stage in the overall process of chromosome segregation.

The organization,regulation,and biological functions of the synaptonemal complex

The synaptonemal complex(SC)is a meiosis-specific proteinaceous macromolecular structure that assembles between paired homologous chromosomes during meiosis in various eukaryotes.The SC has a highly conserved ultrastructure and plays critical roles in controlling multiple steps in meiotic recombination and crossover formation,ensuring accurate meiotic chromosome segregation.Recent studies in different organisms,facilitated by advances in super-resolution microscopy,have provided insights into the macromolecular structure of the SC,including the internal organization of the meiotic chromosome axis and SC central region,the regulatory pathways that control SC assembly and dynamics,and the biological functions exerted by the SC and its substructures.This review summarizes recent discoveries about how the SC is organized and regulated that help to explain the biological functions associated with this meiosis-specific structure.

Ser68 phosphoregulation is essential for CENP-A deposition,centromere function and viability in mice

Centromere identity is defined by nucleosomes containing CENP-A,a histone H3 variant.The deposition of CENP-A at centromeres is tightly regulated in a cell-cycle-dependent manner.We previously reported that the spatiotemporal control of centromeric CENP-A incorporation is mediated by the phosphorylation of CENP-A Ser68.However,a recent report argued that Ser68 phosphoregulation is dispensable for accurate CENP-A loading.Here,we report that the substitution of Ser68 of endogenous CENP-A with either Gln68 or Glu68 severely impairs CENP-A deposition and cell viability.We also find that mice harboring the corresponding mutations are lethal.Together,these results indicate that the dynamic phosphorylation of Ser68 ensures cell-cycle-dependent CENP-A deposition and cell viability.

Maintenance of Genome Stability

It was ever thought that genomic information is transmitted faithfully from generation to generation. But our current knowledge does not indicate that it is the case. For example, genomic variations can be generated from DNA replication infidelity and unequal chromosome segregation. Natural decay of DNA molecules is also a fundamental source of changing genomic information. In addition, cellular and organismal exposure to exogenous genotoxic agents such as ultraviolet （UV） light, oxidative stress, chemical mutagens, and radiation can lead to a variety of modifications on DNA constituents, resulting in genome alterations. Fortunately, cells have evolved several response systems to tackle numerous DNA lesions in order to maintain their genome integrity. Among them, check- point control is probably the most well-known one. For exam- ple, checkpoint responds to replication stress, replication fork stalling, double-strand DNA breaks, and various other types of DNA lesions. Increasing experimental evidence indicates that genomic instability is probably the fundamental reason for carcinogenesis. Genomic instability is also found to be a main etiological factor of neurodegenerative diseases, aging, immunodeficiency, etc. Thus, to understand how cells regulate to maintain their genomic stability is of fundamental importance.