Differential mRNA expression in in vivo produced pre-implantation embryos of dairy heifers and mature cows

Symposium review: Embryo survival-A genomic perspective of the other side of fertility

The majority of embryonic loss in cattle occurs within the first 3 to 4 wk of pregnancy, and there are currently no accurate predictors of pregnancy outcome. Existing embryo quality assessment methods include morphological evaluation and embryo biopsy. These methods are not accurate and carry some health risks to the developing embryo, respectively. Therefore, there is need to identify noninvasive biomarkers such as microRNA that can predict embryo quality and pregnancy outcome. Furthermore, researchers need a better understanding of the dynamic interaction between the mother and the embryo. The transcriptome of the uterus shows plasticity that depends on the embryo type so that the expression level of some genes for in vivo embryos would be different from that of in vitro-produced embryos. Similarly, the embryonic transcriptome and epigenome change in response to different environmental factors such as stress, diet, disease, and physiological status of the mother. This embryo-mother crosstalk could be better understood by investigating the molecular signaling that occurs at different stages of embryonic development. Although transcriptomics is a useful tool to assess the roles of genes and pathways in embryo quality and maternal receptivity, it does not provide the exact functions of these genes, and it shows correlation rather than causality. Therefore, an in-depth functional genomic analysis is needed for better understanding of the molecular mechanisms controlling embryo development. In this review, we discuss recent genomic technologies such as RNA interference, gapmer technology, and genome editing techniques used in humans and livestock to elucidate the molecular mechanisms of genes affecting embryo development.

Effect of bovine follicular fluid on reactive oxygen species and glutathione in oocytes, apoptosis and apoptosis-related gene expression of in vitro-produced blastocysts

The reactive oxygen species (ROS) generated during the in vitro maturation of oocytes affect oocyte maturation and subsequent embryonic development. Bovine follicular fluid (bFF) has an effective antioxidant capacity. This study was conducted to investigate the effects of supplementing oocyte maturation media with bFF from different size classes (3-8 and 9-13 mm) on the glutathione (GSH) and ROS levels of oocytes. Embryonic development and apoptosis, as well as the relative abundance of INFτ, BAX, BCL2 and HSP70 transcripts in blastocysts, were also monitored. Oocytes collected from ovaries were matured in TCM-199 with FBS (control) and 10% 3-8 mm (M), 9-13 mm (L) or a mixture of 3-8 mm and 9-13 mm (M + L) bFF. Glutathione and ROS levels in oocytes after 24 h were assessed by Cell Tracker Blue CMF2HC and DCHFDA staining, respectively. Apoptosis in day-8 blastocysts was assessed by TUNEL staining. The relative abundance of BAX, BCL2, HSP70 and INFτ transcripts was assessed using quantitative real-time polymerase chain reaction (PCR). The GSH level was significantly higher in the L group compared to the other groups (p < 0.05), while the ROS levels in the M group were significantly higher than in the other groups (p < 0.05). The apoptosis levels of blastocysts in the FBS group were significantly higher than those in the M + L group (p < 0.05), although the embryonic development did not differ between the groups. The HSP70 and INFτ expression levels in group M were significantly greater than in the controls (p < 0.05). There was no significant difference in BAX expression between the groups. Supplementation with bFF from various sizes of follicles into the maturation medium was capable of supporting oocyte cytoplasmic maturation by decreasing the ROS. Moreover, bFF subsequently affected antioxidative gene expression, increasing HSP70 and INFτ expressions.

Effects of lactation and pregnancy on gene expression of endometrium of Holstein cows at day 17 of the estrous cycle or pregnancy

Objectives were to determine effects of lactation and pregnancy on endometrial gene expression on d 17 of the estrous cycle and pregnancy. Heifers (n = 33) were assigned randomly after parturition to lactating (L, n = 17) or nonlactating (NL, n = 16) groups. Cows were subjected to an ovulation synchronization program for a timed artificial insemination (TAI); 10 cows in L and 12 in NL were inseminated. Slaughter occurred 17 d after the day equivalent to TAI, and intercaruncular endometrial tissues were collected. Gene expression was determined by DNA microarray analysis for pregnant (L, n = 8; NL, n = 6) and noninseminated cyclic (L, n = 7; NL, n = 4) cows. Differentially expressed genes were selected with a P-value <0.01 and absolute expression >40. In addition, a fold effect >1.5 was used as a criterion for genes affected by pregnancy. In total, 210 genes were differentially regulated by lactation (136 downregulated and 74 upregulated), and 702 genes were differentially regulated by pregnancy (407 downregulated and 295 upregulated). The interaction effect of pregnancy and lactation affected 61 genes. Genes up- and downregulated in pregnant cows were associated with several gene ontology terms, such as defense response and interferon regulatory factor, cell adhesion, and extracellular matrix. The gene ontology analyses of up- and downregulated genes of lactating cows revealed terms related to immunoglobulin-like fold, immune response, COMM domain, and non-membrane-bounded organelle. Several genes upregulated by lactation, such as IGHG1, IGLL1, IGK, and TRD, were related to immune function, particularly for B cells and γδ T cells. Developmental genes related to limb and neural development and glucose homeostasis (e.g., DKK1, RELN, PDK4) were downregulated by lactation, whereas an interaction was also detected for RELN. The stated genes associated with immune function and developmental genes expressed in the endometrium affected by lactational state are possible candidate genes for interventions to improve fertility of lactating dairy cows.

Expression of apoptotic genes in immature and in vitro matured equine oocytes and cumulus cells

The gene expression of Bax, Bcl-2, survivin and p53, following in vitro maturation of equine oocytes, was compared in morphologically distinct oocytes and cumulus cells. Cumulus-oocyte complexes (COC) were harvested and divided into two groups: G1 - morphologically healthy cells; and G2 - less viable cells or cells with some degree of atresia. Total RNA was isolated from both immature and in vitro matured COC and real-time reverse transcription polymerase chain reaction (qRT-PCR) was used to quantify gene expression. Our results showed there was significantly higher expression of survivin (P < 0.05) and lower expression of p53 (P < 0.01) in oocytes compared with cumulus cells in G1. No significant difference in gene expression was observed following in vitro maturation or in COC derived from G1 and G2. However, expression of the Bax gene was significantly higher in cumulus cells from G1 (P < 0.02).

Comparison of expression levels of candidate genes in endometrium of dairy heifers and lactating dairy cows

Pretheeban, T., Gordon, M. B., Singh, R. and Rajamahendran, R. 2011. Comparison of expression levels of candidate genes in endometrium of dairy heifers and lactating dairy cows. Can. J. Anim. Sci. 91: 255–264. Pregnancy rates (PR) in high-producing lactating dairy cows have declined drastically over the past several decades, but those of heifers have remained constant. Reduced PR could be due to multiple causes, and the underlying pathophysiological mechanisms are still unclear. A compromised maternal uterine environment could be one of factors that could affect the PR. This study was performed to compare the nature of the uterine environment in dairy heifers and lactating dairy cows (2nd/3rd parity) by analyzing the expression levels of selected endometrial genes. Estrus was synchronized in heifers (n=5) and lactating dairy cows (n=5) and endometrial biopsies were performed during the mid luteal phase (day 11) of the estrous cycle. Real-time polymerase chain reaction (Q-RT PCR) and immunohistochemistry were performed to analyse the mRNA and protein levels of genes respectively. Relative abundance of BCL2, HSPA1A, IL1A, TNF, IGF1, FGF2 and SERPINA14 transcripts and the protein expression of IL1A, TNF and FGF2 were significantly higher in heifers in comparison with lactating dairy cows. Our findings suggest an altered endometrial environment in lactating dairy cows compared with heifers. However, whether these differences play a role in pregnancy outcomes should be further investigated.

In vivo-derived horse blastocysts show transcriptional upregulation of developmentally important genes compared with in vitro-produced horse blastocysts

In vitro-produced (IVP) equine blastocysts can give rise to successful pregnancies, but their morphology and developmental rate differ from those of in vivo-derived equine blastocysts. The aim of the present study was to evaluate this difference at the genetic level. Suppression subtractive hybridisation (SSH) was used to construct a cDNA library enriched for transcripts preferentially expressed in in vivo-derived equine blastocysts compared with IVP blastocysts. Of the 62 different genes identified in this way, six genes involved in embryonic development (BEX2, FABP3, HSP90AA1, MOBKL3, MCM7 and ODC) were selected to confirm this differential expression by reverse transcription–quantitative real-time polymerase chain reaction (RT-qPCR). Using RT-qPCR, five genes were confirmed to be significantly upregulated in in vivo-derived blastocysts (i.e. FABP3, HSP90AA1 (both P < 0.05), ODC, MOBKL3 and BEX2 (P < 0.005 for all three)), confirming the results of the SSH. There was no significant difference in MCM7 expression between IVP and in vivo-derived blastocysts. In conclusion, five genes that are transcriptionally upregulated in in vivo-derived equine blastocysts compared with IVP blastocysts have been identified. Because of their possible importance in embryonic development, the expression of these genes can be used as a marker to evaluate in vitro embryo production systems in the horse.