Evaluation of morphology, morphometry and follicular dynamics in FecGE genotyped ewes

This study aimed to evaluate the effect of FecG^E mutation on the development of ovarian follicles. To this end, 42 Santa Inês ewes were genotyped for FecG^E mutation and classified as wild-type (FecG^+/+), heterozygous (FecG^+/E) or mutant homozygous (FecG^E/E). Ovarian fragments were processed, and the follicles were analyzed with regard to the morphology and morphometry using classical histology. For the evaluation of follicular dynamics, ewes underwent oestrous synchronization and were monitored throughout an interovulatory period. A higher (P < 0.05) percentage of morphologically normal follicles in the primordial stage was identified in FecG^E/E (90.0%) and FecG^+/E (88.1%) ewes than in the FecG^+/+ (73.0%) ewes. There was also a significantly greater (P < 0.05) number of morphologically normal follicles in the FecG^E/E (87.3%) and FecG^+/E (83.3%) ewes than in FecG^+/+ (76.8%) ewes in the transitional stage. A smaller (P < 0.05) diameter was observed in the secondary follicles in FecG^E/E (93.8 μm) ewes than in FecG^+/E (171.8 μm) ewes. Regarding follicular dynamics, FecG^E/E ewes showed a greater (P < 0.05) number of ovulations (2.5 ± 0.2) than FecG^+/+ ewes (1.5 ± 0.3) ewes. Ovulatory follicles were smaller (P < 0.05) in the FecG^E/E (5.1 mm) and FecG^+/E (5.2 mm) ewes than in FecG^+/+ (5.8 mm) ewes. Santa Inês nulliparous ewes carrying the FecG^E mutation showed a greater proportion of morphologically normal follicles in the primordial and transitional stages than those not carrying the mutation. FecG^E/E ewes demonstrated a higher number of ovulated follicles and that FecG^E/E and FecG^+/E ewes presented ovulatory follicles with a smaller diameter.

Identification of molecular markers for oocyte competence in bovine cumulus cells

Cumulus cells (CCs) have an important role during oocyte growth, competence acquisition, maturation, ovulation and fertilization. In an attempt to isolate potential biomarkers for bovine in vitro fertilization, we identified genes differentially expressed in bovine CCs from oocytes with different competence statuses, through microarray analysis. The model of follicle size, in which competent cumulus-oocyte complexes (COCs) were recovered from bigger follicles (≥8.0 mm in diameter) and less competent ones from smaller follicles (1-3 mm), was used. We identified 4178 genes that were differentially expressed (P < 0.05) in the two categories of CCs. The list was further enriched, through the use of a 2.5-fold change in gene expression as a cutoff value, to include 143 up-regulated and 80 down-regulated genes in CCs of competent COCs compared to incompetent COCs. These genes were screened according to their cellular roles, most of which were related to cell cycle, DNA repair, energy metabolism, metabolism of amino acids, cell signaling, meiosis, ovulation and inflammation. Three candidate genes up-regulated (FGF11, IGFBP4, SPRY1) and three down-regulated (ARHGAP22, COL18A1 and GPC4) in CCs from COCs of big follicles (≥8.1 mm) were selected for qPCR analysis. The selected genes showed the same expression patterns by qPCR and microarray analysis. These genes may be potential genetic markers that predict oocyte competence in in vitro fertilization routines.

Methylation status in the intragenic differentially methylated region of the IGF2 locus in Bos taurus indicus oocytes with different developmental competencies

Oocyte quality is one of the most important aspects of in vitro embryo development. Extensive epigenetic programming must occur during oocyte growth and maturation. A specific DNA methylation pattern of the imprinted genes must be established on differentially methylated regions (DMR). The insulin-like growth factor 2 (IGF2) gene is an important growth factor, and it is imprinted in several mammalian species. The aim of this study was to evaluate the methylation pattern on the DMR of the last exon of IGF2 in immature and mature bovine oocytes with different developmental competencies. Mature oocytes from large follicles were less methylated (28.93%) than immature oocytes from large follicles (77.38% P = 0.002), and there was also a tendency towards lower methylation in mature oocytes from large follicles (28.93%) compared with mature oocytes from small follicles (52.58% P = 0.07). Immature oocytes from small and large follicles showed 53.85% (7/13) and 91.66% (11/12) hypermethylated sequences, respectively, whereas mature oocytes from small and large follicles showed 61.11% (11/18) and 40% (4/10), respectively. The hypomethylation pattern in mature oocytes from large follicles may be related to the higher competence of these oocytes. Our results suggest that the methylation pattern in this DMR may be a useful parameter to investigate as a molecular marker for oocyte competence in cattle and as a model for studies in other species.

239 ALLELE-SPECIFIC EXPRESSION OF X CHROMOSOME-LINKED GENE MAO-A DURING PRE-IMPLANTATION DEVELOPMENT IN BOVINE EMBRYO

The in vitro embryo culture might affect epigenetic mechanisms, which are involved in controlling the expression of genes related to embryonic development and inactivation of X chromosome. Female mammals have 2 X chromosomes, and males have only 1. This has led to a particular mechanism of evolution of dosage compensation, called X-chromosome inactivation, an important epigenetic event that must occur in all mammalian female embryos. During embryogenesis, at the late blastocyst development (Xue F et al. 2002 Nature Genet. 31, 216–220), 1 of the 2 X chromosomes is randomly inactivated in each cell of the inner cell mass and preferentially X paternal in trophoblast. The aim of this study was to characterize the allele-specific expression of the X chromosome-linked gene monoamine oxidase type A (MAO-A) during in vitro pre-implantation embryo development in bovine. For phenotyping of the MAO-A gene, the RT-PCR restriction fragment length polymorphism technique was used. Primers were designed flanking a single nucleotide polymorphism and the sequence of forward inner primer creating a site of restriction to the RsaI enzyme, thus allowing the detection of allele-specific expression (Bos taurus Taurus × Bos taurus indicus). Oocytes were aspirated from 9 Nelore heifers homozygous for theA allele previously genotyped. The oocytes were selected, matured in vitro, and inseminated with X-sorted sperm from a Holstein bull homozygous for the G allele. Two pools of 10 heterozygous in vitro embryos of each developmental stage, 4-cell [44 h post-insemination (p.i.)], 8- to 16-cell (72 h p.i.), morula (144 h p.i.), blastocyst (156 p.i.), and expanded blastocyst (168 h p.i.), were produced and frozen until RNA extraction. Total RNA was extracted using Invisorb® Spin Cell RNA Mini Kit (Invitek, Berlin, Germany) according to the manufacturer’s protocol, and residual genomic DNA was removed with DNase I treatment. cDNA was done using Oligo dT primers (Invitrogen) and superscript III reverse transcriptase (Invitrogen). Nested PCR for each pool was performed and then the amplicons were digested with 10 U of RsaI enzyme (Promega, Madison, WI, USA). The products were separated by electrophoresis on a 3% agarose gel stained with ethidium bromide. The results showed that both alleles were expressionally represented in the 4-cell, 8- to 16-cell, and expanded blastocyst stages, with the X paternal allele disappearing in morula and blastocyst. We can conclude that both, maternal and paternal X chromosomes, are activated in the 2 earliest stages, inactivated in the morula and blastocyst stages, and reactivated in the expanded blastocyst stage. This research was supported by Embrapa Genetic Resources and Biotechnology and the Brazilian National Council for Scientific and Technological Development (CNPq).

Conserved sequences in the beta subunit of archaeal and eukaryal translation initiation factor 2 (eIF2), absent from eIF5, mediate interaction with eIF2gamma

The eukaryotic translation initiation factor 2 (eIF2) binds the methionyl-initiator tRNA in a GTP-dependent mode. This complex associates with the 40 S ribosomal particle, which then, with the aid of other factors, binds to the 5' end of the mRNA and migrates to the first AUG codon, where eIF5 promotes GTP hydrolysis, followed by the formation of the 80 S ribosome. Here we provide a comparative sequence analysis of the beta subunit of eIF2 and its archaeal counterpart (aIF2beta). aIF2beta differs from eIF2beta in not possessing an N-terminal extension implicated in binding RNA, eIF5 and eIF2B. The remaining sequences are highly conserved, and are shared with eIF5. Previously isolated mutations in the yeast eIF2beta, which allow initiation of translation at UUG codons due to the uncovering of an intrinsic GTPase activity in eIF2, involve residues that are conserved in aIF2beta, but not in eIF5. We show that the sequence of eIF2beta homologous to aIF2beta is sufficient for binding eIF2gamma, the only subunit with which it interacts, and comprises, at the most, 78 residues. eIF5 does not interact with eIF2gamma, despite its similarity with eIF2beta, probably because of a gap in homology in this region. These observations have implications for the evolution of the mechanism of translation initiation.