Expression of genes associated with BMP signaling pathway in porcine oocytes before and after IVM - a microarray approach

Long-Term In Vitro Culture Alters Gene Expression Pattern of Genes Involved in Ontological Groups Representing Cellular Processes

The oviduct provides an optimal environment for the final preparation, transport, and survival of gametes, the fertilization process, and early embryonic development. Most of the studies on reproduction are based on in vitro cell culture models because of the cell's accessibility. It creates opportunities to explore the complexity of directly linked processes between cells. Previous studies showed a significant expression of genes responsible for cell differentiation, maturation, and development during long-term porcine oviduct epithelial cells (POECs) in vitro culture. This study aimed at establishing the transcriptomic profile and comprehensive characteristics of porcine oviduct epithelial cell in vitro cultures, to compare changes in gene expression over time and deliver information about the expression pattern of genes highlighted in specific GO groups. The oviduct cells were collected after 7, 15, and 30 days of in vitro cultivation. The transcriptomic profile of gene expression was compared to the control group (cells collected after the first day). The expression of COL1A2 and LOX was enhanced, while FGFBP1, SERPINB2, and OVGP1 were downregulated at all selected intervals of cell culture in comparison to the 24-h control (p-value < 0.05). Adding new detailed information to the reproductive biology field about the diversified transcriptome profile in POECs may create new future possibilities in infertility treatments, including assisted reproductive technique (ART) programmes, and may be a valuable tool to investigate the potential role of oviduct cells in post-ovulation events.

MicroRNA21 inhibition affects porcine oocyte maturation and alters protein expression critical for metabolic pathway function

MicroRNA21 (MIR21) abundance in porcine oocytes and cumulus cells increases during in vitro maturation. The mechanism by which MIR21 regulates oocyte maturation and the effect on the developmental competence of subsequent embryos remains unclear. The objective of this study was to assess the function of MIR21 during porcine oocyte maturation and its effect on embryonic development. Treatment with peptide nucleic acid MIR21 inhibitor (MIR21-PNA), designed to specifically bind to and prevent MIR21 activity during in vitro oocyte maturation, decreased cumulus cell expansion, and the oocyte ability to achieve metaphase II maturation stage when compared to control groups. Following parthenogenetic activation, the cleavage rate at 48 h in the MIR21-PNA group was decreased (p ≤ 0.03) relative to the control groups. Additionally, liquid chromatography-mass spectrometry (LC-MS/MS) of oocyte and cumulus cell total protein following MIR21-PNA treatment during in vitro maturation identified changes in signaling pathways with primary involvement of glucose metabolism (GM) pathways. Furthermore, there was no difference (p = 0.21) in oocyte maturation of control and MIR21-PNA treated oocytes when cultured in pyruvate lacking medium. Finally, MIR21-PNA treatment decreased (p = 0.04) glutathione and increased (p = 0.07) reactive oxygen species production in the oocyte. These data suggest that MIR21 influences porcine oocyte maturation by regulating GM pathways in the cumulus-oocyte complex.

Identification, Molecular Characterization, and Tissue Expression Profiles of Three Smad Genes from Water Buffalo (Bubalus bubalis)

Smads are involved in a variety of biological activities by mediating bone morphogenetic protein (BMP) signals. The full-length coding sequences (CDSs) of buffalo Smads 1, 4, and 5 were isolated and identified through RT-PCR in this study. Their lengths are 1398 bp, 1662 bp, and 1398 bp, respectively. In silico analysis showed that their transcriptional region structures, as well as their amino acid sequences, physicochemical characteristics, motifs, conserved domains, and three-dimensional structures of their encoded proteins are highly consistent with their counterparts in the species of Bovidae. The three Smad proteins are all hydrophilic without the signal peptides and transmembrane regions. Each of them has an MH1 domain and an MH2 domain. A nuclear localization sequence was found in the MH1 domain of buffalo Smads 1 and 5. Prediction showed that the function of the three Smads is mainly protein binding, and they can interact with BMPs and their receptors. The three genes were expressed in all 10 buffalo tissues assayed, and their expression in the mammary gland, gonad, and spleen was relatively high. The results here indicate that the three buffalo Smads may be involved in the transcriptional regulation of genes in a variety of tissues.

Hydroxyurea affects in vitro porcine oocyte maturation through increased apoptosis and oxidative stress

Hydroxyurea (HU) is an FDA-approved drug used to treat a variety of diseases, especially malignancies, but is harmful to fertility. We used porcine oocytes as an experimental model to study the effect of HU during oocyte maturation. Exposure of cumulus–oocyte complexes (COCs) to 20 µM (P<0.01) and 50 µM (P<0.001) HU reduced oocyte maturation. Exposure to 20 µM HU induced approximately 1.5- and 2-fold increases in Caspase-3 (P<0.001) and P53 (P<0.01) gene expression levels in cumulus cells, respectively, increased Caspase-3 (P<0.01) and P53 (P<0.001) protein expression levels in metaphase II (MII) oocytes and increased the percentage of apoptotic cumulus cells (P<0.001). In addition, HU decreased the mitochondrial membrane potential (Δφm) (P<0.01 and P<0.001) and glutathione (GSH) levels (P<0.01 and P<0.001) of both cumulus cells and MII oocytes, while increasing their reactive oxygen species (ROS) levels (P<0.001). Following parthenogenetic activation of embryos derived from MII oocytes, exposure to 20 µM HU significantly reduced total blastocyst cell numbers (P<0.001) and increased apoptosis of blastocyst cells (P<0.001). Moreover, HU exposure reduced the rate of development of two-celled, four- to eight-celled, blastocyst, and hatching stages after parthenogenetic activation (P<0.05). Our findings indicate that exposure to 20 µM HU caused significant oxidative stress and apoptosis of MII oocytes during maturation, which affected their developmental ability. These results provide valuable information for safety assessments of HU.

Long Non-Coding RNA and mRNA Profiling in Early-Stage Bovine Embryos Treated with Glutathione

We measured differential expression profiles of genes and long non-coding RNA (lncRNA) using RNA sequencing in bovine embryos with or without glutathione (GSH) treatment. Bovine embryos fertilized in vitro were treated with GSH to blastocyst. Embryos at the 8-16-cell and morula stages were collected, with embryos without GSH treatment as the control. RNA was isolated, amplified, and sequenced. Differentially expressed genes (DEGs) and lncRNAs (DElncRNAs) were identified and bioinformatic analyses carried out. Transcript levels were confirmed using quantitative RT-PCR. A total of 4100 DEGs were identified, of which 3952 were in GSH-treated morulae and 884 in untreated morulae. More gene ontology (GO) terms were associated with GSH treatment than with control conditions. KEGG analysis showed that glutathione metabolism, citrate cycle, and metabolic pathways involving glycine, serine, and threonine were observed only in GSH-treated embryos. Among 4273 DElncRNAs identified, 59 were potentially important in GSH-treated embryo development, including 14 involved in glutathione metabolism. The 59 DElncRNAs co-expressed with protein-coding mRNAs involved similar GO terms and pathways as the DEGs. This appears to be the first comprehensive profiling of DEGs and DElncRNAs in bovine embryos fertilized in vitro with or without GSH, and the first systematic screen of potential lncRNAs in bovine embryos.

Transcriptomic Pattern of Genes Regulating Protein Response and Status of Mitochondrial Activity Are Related to Oocyte Maturational Competence-A Transcriptomic Study

This paper aims to identify and describe new genetic markers involved in the processes of protein expression and modification reflected in the change of mitochondrial activity before and after in vitro maturation of the oocyte. Porcine oocytes collected from the ovaries of slaughtered landrace gilts were subjected to the process of in vitro maturation. Transcriptomic changes in the expression profile of oocyte genes involved in response to hypoxia, the transmembrane protein receptor serine threonine kinase signaling pathway, the “transforming growth factor β receptor signaling pathway”, “response to protein stimulus”, and “response to organic substance” were investigated using microarrays. The expression values of these genes in oocytes was analyzed before (immature) and after (mature) in vitro maturation, with significant differences found. All the significantly altered genes showed downregulation after the maturation process. The most changed genes from these gene ontologies, FOS, ID2, VEGFA, BTG2, CYR61, ESR1, AR, TACR3, CCND2, CHRDL1, were chosen to be further validated, described and related to the literature. Additionally, the mitochondrial activity of the analyzed oocytes was measured using specific dyes. We found that the mitochondrial activity was higher before the maturation process. The analysis of these results and the available literature provides a novel insight on the processes that occur during in vitro oocyte maturation. While this knowledge may prove to be useful in further research of the procedures commonly associated with in vitro fertilization procedures, it serves mostly as a basic reference for further proteomic, in vivo, and clinical studies that are necessary to translate it into practical applications.

Effects of all-trans retinoic acid on the in vitro maturation of camel (Camelus dromedarius) cumulus-oocyte complexes

All-trans retinoic acid (RA) is a metabolite of vitamin A and has pleiotropic actions on many different biological processes, including cell growth and differentiation, and is involved in different aspects of fertility and developmental biology. In the current study, we investigated the effects of RA on camel (Camelus dromedarius) cumulus-oocyte complex in vitro maturation (IVM). IVM medium was supplemented with 0, 10, 20, and 40 µM RA. Application of 20 µM RA significantly reduced the proportion of degenerated oocytes and significantly improved oocyte meiosis and first polar body extrusion compared to the control and other experimental groups. Retinoic acid significantly reduced the mRNA transcript levels of apoptosis-related genes, including BAX and P53, and reduced the BAX/BCL2 ratio. In addition, RA significantly reduced the expression of the Transforming growth factor beta (TGFβ) pathway-related transcripts associated with the actin cytoskeleton, ACTA2 and TAGLN; however, RA increased TGFβ expression in cumulus cells. The small molecule SB-431542 inhibits the TGFβ pathway by inhibiting the activity of activin receptor-like kinases (ALK-4, ALK-5, and ALK-7); however, combined supplementation with RA during IVM compensated for the inhibitory effect of SB-431542 on cumulus expansion, oocyte meiosis I, and first polar body extrusion in activated oocytes. The current study shows the beneficial effects of RA on camel oocyte IVM and provides a model to study the multifunctional mechanisms involved in cumulus expansion and oocyte meiosis, particularly those involved in the TGFβ pathway.

Fatty Acids Related Genes Expression Undergo Substantial Changes in Porcine Oviductal Epithelial Cells During Long-Term Primary Culture

The process of reproduction requires several factors, leading to successful fertilization of an oocyte by a single spermatozoon. One of them is the complete maturity of an oocyte, which is acquired during long stages of folliculogenesis and oogenesis. Additionally, the oviduct, composed of oviductal epithelial cells (OECs), has a prominent influence on this event through sperm modification and supporting oocyte’s movement towards uterus. OECs were isolated from porcine oviducts. Cells were kept in primary in vitro culture for 30 days. After 24h and on days 7, 15 and 30 cells were harvested, and RNA was isolated. Transcript changes were analyzed using microarrays. Fatty acids biosynthetic process and fatty acids transport ontology groups were selected for analysis and described. Results of this study indicated that majority of genes in both ontology groups were up-regulated on day 7, 15 and 30 of primary in vitro culture. We analyzed genes involved in fatty acids biosynthetic process, including: GGT1, PTGES, INSIG1, SCD, ACSL3, FADS2, FADS1, ACSS2, ALOX5AP, ACADL, SYK, ACACA, HSD17B8, FADS3, OXSM, and transport, including: ABCC2, ACSL4, FABP3, PLA2G3, PPARA, SYK, PPARD, ACACA and P2RX7. Elevated levels of fatty acids in bovine and human oviducts are known to reduce proliferation capacity of OECs and promote inflammatory responses in their microenvironment. Most of measured genes could not be connected to reproductive events. However, the alterations in cellular proliferation, differentiation and genes expression during in vitro long-term culture were significant. Thus, we can treat them as putative markers of changes in OECs physiology.

Cytoplasmic and nuclear maturation of oocytes in mammals – living in the shadow of cells developmental capability

The pig is a polyestrous animal in which the ovarian cycle lasts about 21 days and results in ovulation of 10-25 oocytes. Ovum reaches 120-150 μm in diameter, with the surrounding corona radiata providing communication with the environment. The zona pellucida is composed of glycoproteins: ZP1, ZP2, ZP3. In the course of oogenesis, RNA and protein accumulation for embryonic development occurs. Maternal mRNA is the template for protein production. Nuclear, cytoplasmic and genomic maturity condition the ability of the ovum to undergo fertilization. There are several differences in protein expression profiles observed between in vitro and in vivo conditions. Oogenesis is the process of differentiating female primary sex cells into gametes. During development gonocytes migrate from the yolk sac into the primary gonads with TGF-1, fibronectin, and laminin regulating this process. Cell cycle is blocked in dictyotene. Primary oocyte maturation is resumed before each ovulation and lasts until the next block in metaphase II. At the moment of penetration of the sperm into the ovum, the metaphase block is broken. The oocytes, surrounded by a single layer of granular cells, form the ovarian follicle. The exchange of signals between the oocyte and the cumulus cells done by gap-junctions, as well as various endo and paracrine signals. The contact between the corona radiata cells provides substances necessary for growth, through the same gap junctions. Studies on follicular cells can be used to amplify the knowledge of gene expression in these cells, in order to open way for potential clinical applications.

Significant Down-Regulation of "Biological Adhesion" Genes in Porcine Oocytes after IVM

Proper maturation of the mammalian oocyte is a compound processes determining successful monospermic fertilization, however the number of fully mature porcine oocytes is still unsatisfactory. Since oocytes’ maturation and fertilization involve cellular adhesion and membranous contact, the aim was to investigate cell adhesion ontology group in porcine oocytes. The oocytes were collected from ovaries of 45 pubertal crossbred Landrace gilts and subjected to two BCB tests. After the first test, only granulosa cell-free BCB⁺ oocytes were directly exposed to microarray assays and RT-qPCR (“before IVM” group), or first in vitro matured and then if classified as BCB⁺ passed to molecular analyses (“after IVM” group). As a result, we have discovered substantial down-regulation of genes involved in adhesion processes, such as: organization of actin cytoskeleton, migration, proliferation, differentiation, apoptosis, survival or angiogenesis in porcine oocytes after IVM, compared to oocytes analyzed before IVM. In conclusion, we found that biological adhesion may be recognized as the process involved in porcine oocytes’ successful IVM. Down-regulation of genes included in this ontology group in immature oocytes after IVM points to their unique function in oocyte’s achievement of fully mature stages. Thus, results indicated new molecular markers involved in porcine oocyte IVM, displaying essential roles in biological adhesion processes.

MicroRNAs: tiny molecules with a significant role in mammalian follicular and oocyte development

The genetic regulation of female fertility (follicular development, oocyte maturation and early preimplantation embryo development) involves the spatio-temporal regulation of those genes that play key roles in various stages of the female reproductive axis. MicroRNAs (miRNAs), a class of small non-coding RNAs, are known to regulate the expression of a large proportion of such genes. In recent decades, multiple studies have aimed to determine the roles of these non-coding RNAs in mammalian follicular development, oocyte growth and embryo development. These studies have applied a variety of approaches, including conditional knockout of miRNA biogenesis genes, high-throughput sequencing technologies for pattern recognition in miRNA expression and loss- and gain-of-function of miRNAs in various animal models. In addition to the cellular miRNAs, a large variety of RNAs are found in circulation, being coupled with extracellular vesicles, proteins and lipids. Because of their potential as diagnostic markers for abnormal physiologies, there is increasing interest in the identification of extracellular miRNAs in various biological fluids and spent in vitro culture media. This review focuses on studies addressing the expression and potential role of cellular and extracellular miRNAs in mammalian follicular cell physiology and subsequent ovarian functionality and oocyte maturation.