Actions of putative embryokines on development of the preimplantation bovine embryo to the blastocyst stage

Meta-analysis to determine efficacy of colony-stimulating factor 2 for improving pregnancy success after embryo transfer in cattle

Results have been inconsistent as to whether addition of colony stimulating factor 2 (CSF2) to culture medium improves embryo competence for establishment of pregnancy in cattle and humans. The purpose of the current study was to use all available experiments in cattle concerning effects of CSF2 on pregnancy success after transfer into recipient cattle. The approach was to perform a meta-analysis of all published data sets as well as data from an unpublished experiment described for the first time here. Meta-analysis failed to support the hypothesis that addition of CSF2 to embryo culture medium improves competence of bovine blastocysts to increase pregnancy or calving rates after transfer into recipient females. Thus, its general use as a culture medium additive to increase pregnancy success after embryo transfer is not recommended.

Extraction of Innate Immune Genes in Dairy Cattle and the Regulation of Their Expression in Early Embryos

As more and more of the available genomic data have been published, several databases have been developed for deciphering early mammalian embryogenesis; however, less research has been conducted on the regulation of the expression of natural immunity genes during early embryonic development in dairy cows. To this end, we explored the regulatory mechanism of innate immunity genes at the whole-genome level. Based on comparative genomics, 1473 innate immunity genes in cattle were obtained by collecting the latest reports on human innate immunity genes and updated bovine genome data for comparison, and a preliminary database of bovine innate immunity genes was constructed. In order to determine the regulatory mechanism of innate immune genes in dairy cattle early embryos, we conducted weighted co-expression network analysis of the innate immune genes at different developmental stages of dairy cattle early embryos. The results showed that specific module-related genes were significantly enriched in the MAPK signaling pathway. Protein-protein interaction (PPI) analysis showed gene interactions in each specific module, and 10 of the highest connectivity genes were chosen as potential hub genes. Finally, combined with the results for differential expressed genes (DEGs), ATF3, IL6, CD8A, CD69, CD86, HCK, ERBB3, LCK, ITGB2, LYN, and ERBB2 were identified as the key genes of innate immunity in dairy cattle early embryos. In conclusion, the bovine innate immunity gene set was determined and the co-expression network of innate immunity genes in the early embryonic stage of dairy cattle was constructed by comparing and analyzing the whole genome of bovines and humans. The findings in this study provide the basis for exploring the involvement and regulation of innate immune genes in the early embryonic development of dairy cattle.

Effect of IGFBP-4 during In Vitro Maturation on Developmental Competence of Bovine Cumulus Oocyte Complexes

Insulin-like growth factors (IGFs) are essential for oocyte maturation. Their bioavailability is regulated by their respective binding proteins (IGFBPs) and proteases. IGFBP-4 blocks the biological effects of IGFs. High IGFBP-4 expression has been associated with follicle atresia. We hypothesized that IGFBP-4 affects oocyte developmental competence during maturation. Therefore, the aim of this study was to examine the effect of IGFBP-4 on the developmental rate of bovine cumulus-oocyte complexes (COCs) during in vitro embryo production. Abattoir-derived COCs were matured with rbIGFBP-4 (2000, 540, and 54 ng/mL) compared to a control. Cumulus expansion, oocyte maturation, cleavage, blastocyst, and hatching rates were evaluated. Furthermore, blastocyst gene expression of SOCS2, STAT3, SLC2A1, SLCA3, BAX, and POU5F1 transcripts were quantified using RT-qPCR. No statistical differences were detected among the groups for cumulus expansion, maturation, cleavage, blastocyst rates, or all gene transcripts analyzed. However, at day 8 and 9, the number of total hatching and successfully hatched blastocysts was lower in 2000 ng/mL rbIGFBP-4 compared to the control (day 8: total hatching: 17.1 ± 0.21 vs. 31.2 ± 0.11%, p = 0.02 and hatched blastocyst 6.7 ± 0.31 vs. 21.5 ± 0.14%, p = 0.004; day 9 total hatching 36.4 ± 0.18 vs. 57.7 ± 0.10%, p = 0.009 and hatched blastocyst 18.2 ± 0.21 vs. 38.1 ± 0.11%, p = 0.004). We concluded that high concentrations of rbIGFBP-4 might negatively affect the subsequent ability of the embryo to hatch and possibly compromise further elongation.

Effect of IL-10 and TNF-α on the competence and cryosurvival of in vitro produced Bos indicus embryos

In vitro-produced embryos are constantly exposed to stressful conditions that can lead to the activation of the apoptotic pathway. The nuclear Kappa B factor (NF-κB) is an inflammatory mediator that induces the expression of tumor necrosis factor (TNF-α), a pro-inflammatory cytokine, while interleukin-10 (IL-10), an anti-inflammatory cytokine, inhibits NF-κB activity. This study aimed to investigate the effects of IL-10 and TNF-α on the competence and cryosurvival of in vitro-produced bovine embryos. Embryos were produced in vitro using standard protocols, and Grade I blastocysts were vitrified using the Cryotop method. Non-vitrified and vitrified blastocysts were subjected to the TUNEL assay. In Experiment I, on day 6.5 (156 h post-insemination), the embryos were treated with PBS (control), 50 ng/mL of IL-10, or a combination of 25 ng/mL of TNF-α and 50 ng/mL of IL-10. Embryonic development and apoptotic rates were monitored. In Experiment II, the same groups were set up, with the addition of a group treated with 25 ng/mL of TNF-α alone. Grade I blastocysts were vitrified 5 h after treatment, and cryosurvival was monitored at until 48 h post-warming. The apoptosis rate and total cell number were investigated in the vitrified-hatched blastocysts. IL-10 alone did not affect developmental competence or cryosurvival (P > 0.05). The IL-10-treated embryos, when exposed in combination with TNF-α, presented a detrimental effect (P < 0.05) in the embryonic development of non-vitrified embryos. However, vitrified blastocysts had no negative effect (P > 0.05). The TNF-α treatment reduced (P < 0.05) the re-expansion rate at 6 h post-warming and increased (P < 0.05) the apoptosis rate in vitrified hatched blastocysts, whereas no effect (P > 0.05) of the treatments was detected in the hatching rate and total cell number post-warming. In conclusion, TNF-α has a detrimental effect on embryonic developmental competence and cryosurvival by compromising the development of non-vitrified embryos and apoptotic-related events of vitrified blastocysts, whereas IL-10, when in combination with TNF-α, appears to attenuate the detrimental effects of TNF-α.

Molecular regulators of human blastocyst development and hatching: Their significance in implantation and pregnancy outcome

In humans, blastocyst hatching and implantation events are two sequential, critically linked and rate-limiting events for a prospective pregnancy. These events are regulated by embryo-endometrium derived molecular factors which include hormones, growth factors, cytokines, immune-modulators, cell adhesion molecules and proteases. Due to poor viability of blastocysts, they fail to hatch and implant, leading to a low 'Live Birth Rates', majorly contributing to infertility. Here, embryo-derived biomarkers analysis plays a key role to assess potential biological viability of blastocysts which are capable of implantation and prospective pregnancy. Thus far, embryo-derived biomarkers examined are mostly immune-modulators which are thought to be associated with blastocyst development-implantation and progression of pregnancy, leading to live births. There is an urgent need to develop a quantitative and a reliable non-invasive approach aiding embryo selection for elective single embryo transfer and to minimize recurrent pregnancy loss and multiple pregnancies. In this article, we provide a comprehensive review on our current knowledge and understanding of potential embryo-derived molecular regulators, that is, biomarkers, of development of human blastocysts, their hatching and implantation. We discuss their potential implications in the assessment of blastocyst implantation potential and pregnancy outcome in terms of live births in humans.

Bioactive supplements influencing bovine in vitro embryo development

Ovum pickup and in vitro production (IVP) of bovine embryos are replacing traditional multiple ovulation embryo transfer (MOET) as the primary means for generating transferable embryos from genetically elite sires and dams. However, inefficiencies in the IVP process limit the opportunities to produce large numbers of transferable embryos. Also, the post-transfer competency of IVP embryos is inferior to embryos produced by artificial insemination or MOET. Numerous maternal, paternal, embryonic, and culture-related factors can have adverse effects on IVP success. This review will explore the various efforts made on describing how IVP embryo development and post-transfer competency may be improved by supplementing hormones, growth factors, cytokines, steroids and other bioactive factors found in the oviduct and uterus during early pregnancy. More than 40 of these factors, collectively termed as embryokines, are reviewed here. Several embryokines contain abilities to promote embryo development, including improving embryo survivability, improving blastomere cell numbers, and altering the distribution of blastomere cell types in blastocysts. A select few embryokines also can benefit pregnancy retention after IVP embryo transfer and improve neonatal calf health and performance, although very few embryokine-supplemented embryo transfer studies have been completed. Also, supplementing several embryokines at the same time holds promise for improving IVP embryo development and competency. However, more work is needed to explore the post-transfer consequences of adding these putative embryokines for any adverse outcomes, such as large offspring syndrome and poor postnatal health, and to specify the specific embryokine combinations that will best represent the ideal conditions found in the oviduct and uterus.

Actions of DKK1 on the preimplantation bovine embryo to affect pregnancy establishment, placental function and postnatal phenotype†

One mechanism by which the maternal environment regulates the early embryo is by secretion of cell-signaling molecules. One of these is dickkopf WNT signaling pathway inhibitor 1 (DKK1). Objectives were to A) resolve discrepancies in the literature regarding effects of DKK1 in the bovine embryo on development of trophectoderm (TE) and competence to establish pregnancy after embryo transfer and B) determine whether there are long-term consequences of DKK1 on placental function and postnatal phenotype. Embryos produced in vitro were cultured with vehicle or 100 ng/mL recombinant human DKK1 from day 5 to 7.5 of development (i.e. the morula and blastocyst stages of development). DKK1 increased the number of cells positive for the TE marker CDX2 at day 7.5 of development while having no effect on numbers of cells positive for the inner cell mass marker SOX2. There was no effect of DKK1 on pregnancy or calving rate after transfer of blastocysts produced with Y-sorted semen to either lactating dairy cows or suckling beef cows. Treatment with DKK1 at the morula-to-blastocyst stages programmed placental function, as measured by an effect of DKK1 on plasma concentrations of pregnancy associated glycoproteins and placental lactogen at day 160 of gestation (although not on other days examined). DKK1 treatment also resulted in calves that were heavier at birth as compared to calves derived from control embryos. After birth, DKK1 calves grew slower than controls. Results confirm that DKK1 alters the developmental program of the bovine embryo to affect both prenatal and postnatal phenotype.

Actions of CSF2 and DKK1 on bovine embryo development and pregnancy outcomes are affected by composition of embryo culture medium

Procedures for in vitro embryo production in cattle have not been optimized. In the current experiment, we utilized a 3 × 3 factorial design to test whether the proportion of embryos becoming blastocysts in culture and the pregnancy rate after embryo transfer are affected by type of serum in the medium [no serum; 3% (v/v) KnockOut Serum Replacement (SR); 3% (v/v) fetal bovine serum (FBS)] and addition of specific embryokines [vehicle; 10 ng/mL colony stimulating factor 2 (CSF2); 100 ng/mL dickkopf related protein 1 (DKK1)] at day 5 of culture. Embryos were produced using abattoir-derived ovaries and Y-sorted semen from two Angus sires. The percent of putative zygotes and cleaved embryos becoming blastocysts was improved by SR and FBS. Pregnancy rate at day 30 was determined for 1426 Nelore recipients and calving rate for 266 recipients. In the absence of CSF2 or DKK1, pregnancy rates were lower for embryos cultured with SR or FBS. CSF2 and DKK1 reduced pregnancy rate for embryos cultured without serum but had no detrimental effect in the SR or FBS groups. Indeed, CSF2 blocked the negative effect of FBS on pregnancy rate. Data on birth weights were available for 67 bull calves. There were no effects of treatment. The sire used to produce embryos had significant and large effects on development to the blastocyst stage, pregnancy rate at day 30, calving rate and pregnancy loss between day 30 and calving. Results indicate that (1) SR and FBS can improve embryonic development in vitro while also compromising competence of embryos to survive after transfer, (2) actions of CSF2 and DKK1 depend upon other characteristics of the embryo production system, and (3) sire can have a large effect on embryonic development before and after transfer.

Proteomic determinants of uterine receptivity for pregnancy in early and mid-postpartum dairy cows†

Dairy cow subfertility is a worldwide issue arising from multiple factors. It manifests in >30% early pregnancy losses in seasonal pasture-grazed herds, especially when cows are inseminated in the early post-partum period. Most losses occur before implantation, when embryo growth depends on factors present in maternal tract fluids. Here we examined the proteomic composition of early and mid-postpartum uterine luminal fluid in crossbred lactating dairy cows to identify molecular determinants of fertility. We also explored changes in uterine luminal fluid from first to third estrus cycles postpartum in individual cows, linking those changes with divergent embryo development. For this, we flushed uteri of 87 cows at day 7 of pregnancy at first and third estrus postpartum, recovering and grading their embryos. Out of 1563 proteins detected, 472 had not been previously reported in this fluid, and 408 were predicted to be actively secreted by bioinformatic analysis. The abundance of 18 proteins with roles in immune regulation and metabolic function (e.g. cystatin B, pyruvate kinase M2) was associated with contrasting embryo quality. Matched-paired pathway analysis indicated that, from first to third estrus postpartum, upregulation of metabolic (e.g. creatine and carbohydrate) and immune (e.g. complement regulation, antiviral defense) processes were related to poorer quality embryos in the third estrus cycle postpartum. Conversely, upregulated signal transduction and protein trafficking appeared related to improved embryo quality in third estrus. These results advance the characterization of the molecular environment of bovine uterine luminal fluid and may aid understanding fertility issues in other mammals, including humans.

Atlas of receptor genes expressed by the bovine morula and corresponding ligand-related genes expressed by uterine endometrium

Regulation of the mammalian embryo involves cell‐signaling molecules produced by the maternal oviduct and endometrium. Here, datasets on the transcriptome of the gestational Days 5 and 6 bovine morula and Day 5 maternal endometrium were examined to identify receptor genes expressed by the morula and expression of the corresponding ligand‐related genes in the endometrium. A total of 175 receptor genes were identified in the morula, including 48 encoding for growth factors or WNT signaling molecules, 25 for cytokines and chemokines, 35 involved in juxtacrine and matricellular signaling and 25 encoding for receptors for small molecules. Some of the highly‐expressed pairs of endometrial ligand and embryo receptor genes included MDK and its receptors ITGB1, SDC4 and LRP2, WNT5A (RYK), VEGFA (ITGB1), GPI (AMFR), and the hedgehog proteins IHH and DHH (HHIP). The most highly expressed receptors for small molecules were GPRC5C (retinoic acid receptor), PGRMC1 (progesterone), and CHRNB2 (acetylcholine). There were also 84 genes encoding for cell signaling ligands expressed by the morula, with the most highly expressed being GPI, AIMP1, TIMP1, IK, and CCN2. The atlas of receptor and ligand genes should prove useful for understanding details of the communication between the embryo and mother that underlies optimal embryonic development.

Cytokines That Serve as Embryokines in Cattle

Simple Summary

This review will explore how some cytokines also influence early embryonic development. We term these types of molecules as embryokines. Understanding how cytokines serve as embryokines could offer new opportunities to improve embryo development and the overall health of the embryo so that pregnancies will be retained after embryo transfer and so that viable offspring are produced. At least two cytokines may offer these benefits to bovine embryos produced in vitro. Additional cytokines also are identified in this review that may contain beneficial activities on bovine embryos.

Abstract

The term “embryokine” has been used to denote molecules produced by the endometrium, oviduct, or by embryo itself that will influence embryo development. Several cytokines have been identified as embryokines in cattle and other mammals. This review will describe how these cytokines function as embryokines, with special emphasis being placed on their actions on in vitro produced (IVP) bovine embryos. Embryokines are being explored for their ability to overcome the poor development rates of IVP embryos and to limit post-transfer pregnancy retention efficiencies that exist in IVP embryos. This review will focus on describing two of the best-characterized cytokines, colony-stimulating factor 2 and interleukin 6, for their ability to modify bovine embryo quality and confirmation, promote normal fetal development, and generate healthy calves. Additional cytokines will also be discussed for their potential to serve as embryokines.

Interleukin-6 supplementation improves post-transfer embryonic and fetal development of in vitro-produced bovine embryos

The use of in vitro produced embryos in dairy and beef cattle has increased in recent years, but compromised post-transfer pregnancy success prevents producers from capturing all the benefits this technology can provide. This study explored whether supplementing interleukin-6 (IL6) during in vitro embryo development influences post-transfer development of the embryo-proper, fetus and placenta during early gestation in cattle. Slaughterhouse-derived cumulus oocyte complexes underwent IVM (day -1) and IVF (day 0). On day 5 post-fertilization, embryos were treated with either 0 (CONT) or 100 ng/mL recombinant bovine IL6. No difference in blastocyst formation was detected on day 7.5 post-fertilization, but an increase (P < 0.05) in inner cell mass cell numbers and tendency for increased (P = 0.08) trophectoderm cell numbers were detected in IL6-treated blastocysts. A subset of the blastocysts was loaded individually into transfer straws, and embryo transfer (ET) was completed using estrous cycle stage-matched, nonlactating commercial beef and dairy cows. A subset of cows from each group underwent timed artificial insemination (TAI). Pregnancy rates were similar among all three treatment groups at day 28 and 70. No differences in crown-rump length (CRL), crown nose length (CNL), abdominal diameter (AD), or placental fluid volume (PFV) were detected between TAI and ET-IL6 groups. Reductions (P < 0.05) in CRL and AD were detected at day 56 and a tendency for a reduction (P = 0.08) in PFV was detected on day 35 when comparing the ET-CONT group with the TAI group. Reductions (P < 0.05) in CRL and PFV on day 28 and CNL and AD on day 56 as well as a tendency for a reduction (P = 0.08) in PFV on day 35 were detected when contrasting ET-CONT with ET-IL6. Circulating plasma pregnancy-associated glycoprotein concentrations were similar among all treatment groups. In summary, IL6 treatment to IVP embryos before ET produced pregnancies that more closely resembled TAI-generated pregnancies than pregnancies generated using conventionally cultured embryos. These findings failed to find any adverse effects of IL6 supplementation on early development of the embryo-proper and fetus or on placental activity. Rather, these observations suggest that IL6 treatment may normalize the developmental trajectory of the embryo-proper and fetus for in vitro produced embryos.