Meiotic Silencing in Pigs: A Case Study in a Translocated Azoospermic Boar

Carriers of balanced constitutional reciprocal translocations usually present a normal phenotype, but often show reproductive disorders. For the first time in pigs, we analyzed the meiotic process of an autosome–autosome translocation associated with azoospermia. Meiotic process analysis revealed the presence of unpaired autosomal segments with histone γH2AX accumulation sometimes associated with the XY body. Additionally, γH2AX signals were observed on apparently synapsed autosomes other than the SSC1 or SSC15, as previously observed in Ataxia with oculomotor apraxia type 2 patients or knock-out mice for the Senataxin gene. Gene expression showed a downregulation of genes selected on chromosomes 1 and 15, but no upregulation of SSCX genes. We hypothesized that the total meiotic arrest observed in this boar might be due to the silencing of crucial autosomal genes by the mechanism referred to as meiotic silencing of unsynapsed chromatin (MSUC).

MAT heterozygosity and the second sterility barrier in the reproductive isolation of Saccharomyces species

The genetic analysis of large numbers of Saccharomyces cerevisiae × S. uvarum (“cevarum”) and S. kudriavzevii × S. uvarum (“kudvarum”) hybrids in our previous studies revealed that these species are isolated by a postzygotic double-sterility barrier. We proposed a model in which the first barrier is due to the abruption of the meiotic process by the failure of the chromosomes of the subgenomes to pair (and recombine) in meiosis and the second barrier is assumed to be the result of the suppression of mating by allospecific MAT heterozygosity. While the former is analogous to the major mechanism of postzygotic reproductive isolation in plants and animals, the latter seems to be Saccharomyces specific. To bolster the assumed involvement of MAT in the second sterility barrier, we produced synthetic alloploid two-species cevarum and kudvarum hybrids with homo- and heterothallic backgrounds as well as three-species S. cerevisiae × S. kudvarum × S. uvarum (“cekudvarum”) hybrids by mass-mating and examined their MAT loci using species- and cassette-specific primer pairs. We found that the allospecific MAT heterozygosity repressed MAT switching and mating in the hybrids and in the viable but sterile spores produced by the cevarum hybrids that had increased (allotetraploid) genomes. The loss of heterozygosity by meiotic malsegregation of MAT-carrying chromosomes in the latter hybrids broke down the sterility barrier. The resulting spores nullisomic for the S. uvarum chromosome produced vegetative cells capable of MAT switching and conjugation, opening the way for GARMe (Genome Autoreduction in Meiosis), the process that leads to chimeric genomes.

SPAG4L/SPAG4Lβ interacts with Nesprin2 to participate in the meiosis of spermatogenesis

SUN domain proteins are identified as a novel family of nuclear envelope proteins which are involved in spermatogenesis. SPAG4L is identified as the fifth member of this family. Previous studies have revealed that SPAG4L is involved in spermatogenesis and the mutations occurring in SPAG4L will lead to male infertility. However, the transcriptions of SPAG4L and its interacting proteins in the testis are still unclear. In this study, we identified a shorter transcript variant of SPAG4L, named SPAG4Lβ, in human testis by northern blot and reverse transcription-polymerase chain reaction. Bioinformatics analysis showed that it encodes a protein consisting of 311 amino acids, and subcellular localization analysis revealed that it is mainly expressed in the cytoplasm. In situ hybridization and immunofluorescence assay revealed that SPAG4L/SPAG4Lβ is involved in meiosis. Furthermore, co-IP results demonstrated that SPAG4L/SPAG4Lβ interacts with Nesprin2, a KASH domain protein to form the LINC (linker of nucleoskeleton and cytoskeleton) complexes. Immunofluorescence results revealed that the LINC complexes of Spag4l/Nesprin2 in mouse are involved in spermatocyte division. Our data indicated that SPAG4L/SPAG4Lβ may play an important role in the meiotic process.

Development of a Transformation Method for Metschnikowia borealis and other CUG-Serine Yeasts

Yeasts belonging to the Metschnikowia genus are particularly interesting for the unusual formation of only two needle-shaped ascospores during their mating cycle. Presently, the meiotic process that can lead to only two spores from a diploid zygote is poorly understood. The expression of fluorescent nuclear proteins should allow the meiotic process to be visualized in vivo; however, no large-spored species of Metschnikowia has ever been transformed. Accordingly, we aimed to develop a transformation method for Metschnikowia borealis, a particularly large-spored species of Metschnikowia, with the goal of enabling the genetic manipulations required to study biological processes in detail. Genetic analyses confirmed that M. borealis, and many other Metschnikowia species, are CUG-Ser yeasts. Codon-optimized selectable markers lacking CUG codons were used to successfully transform M. borealis by electroporation and lithium acetate, and transformants appeared to be the result of random integration. Mating experiments confirmed that transformed-strains were capable of generating large asci and undergoing recombination. Finally, random integration was used to transform an additional 21 yeast strains, and all attempts successfully generated transformants. The results provide a simple method to transform many yeasts from an array of different clades and can be used to study or develop many species for various applications.

Development of a Transformation Method for Metschnikowia borealis and Other CUG-Serine Yeasts

Yeasts belonging to the Metschnikowia genus are particularly interesting for the unusual formation of only two needle-shaped ascospores during their mating cycle. Presently, the meiotic process that can lead to only two spores from a diploid zygote is poorly understood. The expression of fluorescent nuclear proteins should allow the meiotic process to be visualized in vivo; however, no large-spored species of Metschnikowia has ever been transformed. Accordingly, we aimed to develop a transformation method for Metschnikowia borealis, a particularly large-spored species of Metschnikowia, with the goal of enabling the genetic manipulations required to study biological processes in detail. Genetic analyses confirmed that M. borealis, and many other Metchnikowiacea, are CUG-Ser yeasts. Codon-optimized selectable markers lacking CUG codons were used to successfully transform M. borealis by electroporation and lithium acetate, and transformants appeared to be the result of random integration. Mating experiments confirmed that transformed-strains were capable of generating large asci and undergoing recombination. Finally, random integration was used to transform an additional 18 yeast strains, and all attempts successfully generated transformants. The results provide a simple method to transform many yeasts from an array of different clades and can be used to study or develop many species for various applications.

210 POST-TRANSLATIONAL MODIFICATION OF HISTONE H4 ACETYLATION DURING IN VITRO MATURATION OF CANINE OOCYTES

Proper in vitro oocyte maturation, crucial for in vitro fertilisation, is poorly understood and inefficient in dogs. Post-translational modifications of histones are involved in the meiotic process and preparation of oocytes for fertilisation. The present study aimed to evaluate post-translational histone H4 acetylation at lysine 12 (H4K12ac) and 16 (H4K16ac) in canine oocytes during in vitro maturation (IVM). Ovaries were retrieved from 1–7 year-old bitches undergoing routine ovariohysterectomy (OH). Grade I cumulus-oocyte complexes (COC) were recovered and evaluated before and after IVM in TCM 199 + 0.025 mM sodium pyruvate + 100 000 IU mL–1 penicillin G sodium + 100 mg mL–1 streptomycin sulfate, 0.003 g mL–1 BSA + 50 μL mL–1 Pluset® (500 UI FSH + 500 UI LH) + 1 μL mL–1 insulin-like growth factor (IGF) at 38.5°C in 5% CO2 for 72 h. After IVM, the nuclear stage of oocytes was established using Hoechst 33342 staining, and the acetylation patterns were investigated by indirect immunofluorescence staining of fixed immature and post-IVM oocytes (4% paraformaldehyde) with specific antibodies against the acetylated lysine residues, H4K12ac and H4K16ac. All stages were collected and evaluated simultaneously, and the experiment was repeated 4 times, with a total of 5–14 of oocytes evaluated per stage. Immunofluorescence signal was quantified using the NIH ImageJ software 1.4, and data are presented as a percentage of the average fluorescence intensity of each specific antibody over the intensity of DNA, as determined by Hoescht staining. Immunofluorescence values were analysed using the least square ANOVA by the general linear model procedures of SAS (SAS Institute, Cary, NC, USA), and comparisons of means were further performed by Fisher’s Exact test. A probability level of P < 0.05 was considered significant. Our results indicate a variation in acetylation levels of H4K12 (P < 0.02) and H4K16 (P < 0.04) during meiosis. Fluorescence levels of H4K12ac decreased significantly when comparing immature (2.19 ± 0.62) with oocytes in metaphase I/II (MI/MII) (0.52 ± 0.14). Similarly, H4K16ac displayed a greater acetylation pattern in immature oocytes (1.20 ± 0.27) when compared to oocytes in germinal vesicle breakdown (GVBD; 0.58 ± 0.16) and MI/MII (0.62 ± 0.07) stages. These results support the hypothesis that, similar to other domestic species, post-translational modification of histone acetylation takes place during the meiotic process of oocyte IVM. Whether these histone modifications take place in a similar fashion during IVM remains to be investigated.

Contribution of Structural Chromosome Mutants to the Study of Meiosis in Plants

Dissection of the molecular mechanisms underlying the transition through the complex events of the meiotic process requires the use of gene mutants or RNAi-mediated gene silencing. A considerable number of meiotic mutants have been isolated in plant species such as Arabidopsis thaliana, maize or rice. However, structural chromosome mutants are also important for the identification of the role developed by different chromosome domains in the meiotic process. This review summarizes the contribution of studies carried out in plants using structural chromosome variations. Meiotic events concerning the search of the homologous partner, the control of number and distribution of chiasmata, the mechanism of pairing correction, and chromosome segregation are considered.

100 Gy60Coγ-Ray Induced Novel Mutations in Tetraploid Wheat

10 accessions of tetraploid wheat were radiated with 100 Gy60Coγ-ray. The germination energy, germination rate, special characters (secondary tillering, stalk with wax powder, and dwarf), meiotic process, and high-molecular-weight glutenin subunits (HMW-GSs) were observed. Different species has different radiation sensibility. With 1 seed germinated (5%),T. dicoccum(PI434999) is the most sensitive to this dose of radiation. With a seed germination rate of 35% and 40%, this dose also affectedT. polonicum(As304) andT. carthlicum(As293). Two mutant dwarf plants,T. turgidum(As2255) 253-10 andT. polonicum(As302) 224-14, were detected. Abnormal chromosome pairings were observed in pollen mother cells of bothT. dicoccoides(As835) 237-9 andT. dicoccoides(As838) 239-8 with HMW-GS 1Ax silent in seeds from them. Compared with the unirradiated seed ofT. polonicum(As304) CK, a novel HMW-GS was detected in seed ofT. polonicum(As304) 230-7 and its electrophoretic mobility was between 1By8 and 1Dy12 which were the HMW-GSs of Chinese Spring. These mutant materials would be resources for wheat breeding.

Finding the Correct Partner: The Meiotic Courtship

Homologous chromosomes are usually separated at the entrance of meiosis; how they become paired is one of the outstanding mysteries of the meiotic process. Reduction of spacing between homologues makes possible the occurrence of chromosomal interactions leading to homology detection and the formation of bivalents. In many organisms, telomere-led chromosome movements are generated that bring homologues together. Additional movements produced by chromatin conformational changes at early meiosis may also facilitate homologous contacts. Organisms used in the study of meiosis show a surprising variety of strategies for homology detection. In dipterans, homologous chromosomes remain paired throughout most of development. Pairing seems to arise as a balance between promoter and suppressor pairing genes. Some fungi, plants and animals, use mechanisms based on recombinational interactions. Other mechanisms leading to homology search are recombination-independent and require specialized pairing sites. In the wormCaenorhabditis elegans, each chromosome carries a pairing center consisting of a chromosome-specific DNA-protein complex, and in the fission yeastSchizosaccharomyces pombe, thesme2locus encodes a meiosis-specific non-coding RNA that mediates on homologous recognition. In addition, mismatch correction plays a relevant role, especially in polyploids, which evolved genetic systems that suppress pairing between non-homologous related (homoeologus) chromosomes.