Vascularization and VEGF expression altered in bovine yolk sacs from IVF and NT technologies

Human recombinant interleukin-6 improves the morphological quality of cryopreserved in vitro produced bovine blastocysts

This work explored whether a well-characterized recombinant human interleukin-6 (hIL6) protein will influence in vitro produced (IVP) bovine embryo development and survival after cryopreservation. Cumulus oocyte complexes were collected from abattoir derived ovaries, matured for 24 h, and fertilized using pooled semen from Holstein bulls. Embryos were treated with 0, 25, 50, or 100 ng/mL hIL6 on day 5 post-fertilization. An increase in ICM cell numbers was observed in each hIL6 treatment, with the lowest hIL6 treatment having the same magnitude of response as the middle and highest hIL6 concentration. No effects on TE cell numbers were observed. The second study involved cryopreserving (via slow freezing) of hIL6-treated blastocysts, then examining post-thaw blastocyst survival by incubating for 24 h in the absence of hIL6 treatments. Blastocyst re-expansion and hatching rates were unaffected by any of the IL6 treatments, however, increases in both ICM and TE cell numbers were detected at 24 h post-thawing in blastocysts exposed to 100 ng/mL hIL6 but not lower concentrations before freezing. A reduction in the percentage of TUNEL-positive TE cells was observed after thawing in blastocysts exposed to 25, 50 and 100 ng/mL hIL6 before cryopreservation. No treatment-dependent changes in TUNEL-positive ICM cells were observed. In summary, hIL6 supplementation improves ICM cell numbers in bovine blastocysts to a degree that is commensurate with what has been observed when using bovine recombinant IL6. This positive effect of hIL6 on ICM cell numbers is maintained after freezing and thawing, and a novel improvement in post-thaw TE cell numbers occur in hIL6 treated embryos. This positive effect on TE cell numbers is attributed, at least in part, to an hIL6-dependent reduction in TE cell apoptosis.

Identifying Regions of the Genome Associated with Conception Rate to the First Service in Holstein Heifers Bred by Artificial Insemination and as Embryo Transfer Recipients

Heifer conception rate to the first service (HCR1) is defined as the number of heifers that become pregnant to the first breeding service compared to the heifers bred. This study aimed to identify loci associated and gene sets enriched for HCR1 for heifers that were bred by artificial insemination (AI, n = 2829) or were embryo transfer (ET, n = 2086) recipients, by completing a genome-wide association analysis and gene set enrichment analysis using SNP data (GSEA-SNP). Three unique loci, containing four positional candidate genes, were associated (p < 1 × 10-5) with HCR1 for ET recipients, while the GSEA-SNP identified four gene sets (NES ≥ 3) and sixty-two leading edge genes (LEGs) enriched for HCR1. While no loci were associated with HCR1 bred by AI, one gene set and twelve LEGs were enriched (NES ≥ 3) for HCR1 with the GSEA-SNP. This included one gene (PKD2) shared between HCR1 AI and ET services. Identifying loci associated or enriched for HCR1 provides an opportunity to use them as genomic selection tools to facilitate the selection of cattle with higher reproductive efficiency, and to better understand embryonic loss.

Adipokines in pregnancy

Reproductive success consists of a sequential events chronology, starting with the ovum fertilization, implantation of the embryo, placentation, and cellular processes like proliferation, apoptosis, angiogenesis, endocrinology, or metabolic changes, which taken together finally conduct the birth of healthy offspring. Currently, many factors are known that affect the regulation and proper maintenance of pregnancy in humans, domestic animals, or rodents. Among the determinants of reproductive success should be distinguished: the maternal microenvironment, genes, and proteins as well as numerous pregnancy hormones that regulate the most important processes and ensure organism homeostasis. It is well known that white adipose tissue, as the largest endocrine gland in our body, participates in the synthesis and secretion of numerous hormones belonging to the adipokine family, which also may regulate the course of pregnancy. Unfortunately, overweight and obesity lead to the expansion of adipose tissue in the body, and its excess in both women and animals contributes to changes in the synthesis and release of adipokines, which in turn translates into dramatic changes during pregnancy, including those taking place in the organ that is crucial for the proper progress of pregnancy, i.e. the placenta. In this chapter, we are summarizing the current knowledge about levels of adipokines and their role in the placenta, taking into account the physiological and pathological conditions of pregnancy, e.g. gestational diabetes mellitus, preeclampsia, or intrauterine growth restriction in humans, domestic animals, and rodents.

Influences of Supplementing Selective Members of the Interleukin-6 Cytokine Family on Bovine Oocyte Competency

This work explored whether supplementing selective members of the interleukin-6 (IL6) cytokine family during in vitro bovine oocyte maturation affects maturation success, cumulus-oocyte complex (COC) gene expression, fertilization success, and embryo development potential. Human recombinant proteins for IL6, IL11, and leukemia inhibitory factor (LIF) were supplemented to COCs during the maturation period, then fertilization and embryo culture commenced without further cytokine supplementation. The first study determined that none of these cytokines influenced the rate that oocytes achieved arrest at meiosis II. The second study identified that LIF and IL11 supplementation increases AREG transcript abundance. Supplementation with IL6 supplementation did not affect AREG abundance but reduced HAS2 transcript abundance. Several other transcriptional markers of oocyte competency were not affected by any of the cytokines. The third study determined that supplementing these cytokines during maturation did not influence fertilization success, but either LIF or IL11 supplementation increased blastocyst development. No effect of IL6 supplementation on subsequent blastocyst development was detected. The fourth experiment explored whether each cytokine treatment affects the post-thaw survivability of cryopreserved IVP blastocysts. None of the cytokines supplemented during oocyte maturation produced any positive effects on post-thaw blastocyst re-expansion and hatching. In conclusion, these outcomes implicate IL11 and LIF as potentially useful supplements for improving bovine oocyte competency.

Developmental Hurdles That Can Compromise Pregnancy during the First Month of Gestation in Cattle

Several key developmental events are associated with early embryonic pregnancy losses in beef and dairy cows. These developmental problems are observed at a greater frequency in pregnancies generated from in-vitro-produced bovine embryos. This review describes critical problems that arise during oocyte maturation, fertilization, early embryonic development, compaction and blastulation, embryonic cell lineage specification, elongation, gastrulation, and placentation. Additionally, discussed are potential remediation strategies, but unfortunately, corrective actions are not available for several of the problems being discussed. Further research is needed to produce bovine embryos that have a greater likelihood of surviving to term.

Leukemia Inhibitory Factor Stimulates Primitive Endoderm Expansion in the Bovine Inner Cell Mass

Previous work determined that bovine interleukin-6 (IL6) increases inner cell mass (ICM), primitive endoderm (PE), and total cell number in in vitro produced (IVP) bovine blastocysts. Another IL6 family member, leukemia inhibitory factor (LIF), has the potential to produce the same effects of IL6 due to the presence of its receptor in bovine blastocysts. We compared the abilities of LIF and IL6 to increase ICM cell numbers in day 7, 8, and 9 IVP bovine blastocysts. Supplementation with 100 ng/ml LIF from day 5 onward improved blastocyst formation rates on days 7 and 8 similar to what was observed when supplementing 100 ng/ml IL6. However, LIF supplementation did not cause an increase in ICM numbers like was observed after supplementing IL6. On day 9, increases in PE cell numbers were detected after LIF supplementation, but 300 ng/ml LIF was required to achieve the same effect on PE numbers that was observed by providing 100 ng/ml IL6. Collectively, these results show that LIF can mimic at least some of the effects of IL6 in bovine blastocyst.

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.

Pluripotency and Growth Factors in Early Embryonic Development of Mammals: A Comparative Approach

The regulation of early events in mammalian embryonic development is a complex process. In the early stages, pluripotency, cellular differentiation, and growth should occur at specific times and these events are regulated by different genes that are expressed at specific times and locations. The genes related to pluripotency and cellular differentiation, and growth factors that determine successful embryonic development are different (or differentially expressed) among mammalian species. Some genes are fundamental for controlling pluripotency in some species but less fundamental in others, for example, Oct4 is particularly relevant in bovine early embryonic development, whereas Oct4 inhibition does not affect ovine early embryonic development. In addition, some mechanisms that regulate cellular differentiation do not seem to be clear or evolutionarily conserved. After cellular differentiation, growth factors are relevant in early development, and their effects also differ among species, for example, insulin-like growth factor improves the blastocyst development rate in some species but does not have the same effect in mice. Some growth factors influence genes related to pluripotency, and therefore, their role in early embryo development is not limited to cell growth but could also involve the earliest stages of development. In this review, we summarize the differences among mammalian species regarding the regulation of pluripotency, cellular differentiation, and growth factors in the early stages of embryonic development.

Interleukin-6 promotes primitive endoderm development in bovine blastocysts

Background

Interleukin-6 (IL6) was recently identified as an embryotrophic factor in bovine embryos, where it acts primarily to mediate inner cell mass (ICM) size. This work explored whether IL6 affects epiblast (EPI) and primitive endoderm (PE) development, the two embryonic lineages generated from the ICM after its formation. Nuclear markers for EPI (NANOG) and PE (GATA6) were used to differentiate the two cell types.

Results

Increases (P < 0.05) in total ICM cell numbers and PE cell numbers were detected in bovine blastocysts at day 8 and 9 post-fertilization after exposure to 100 ng/ml recombinant bovine IL6. Also, IL6 increased (P < 0.05) the number of undifferentiated ICM cells (cells containing both PE and EPI markers). The effects of IL6 on EPI cell numbers were inconsistent. Studies were also completed to explore the importance of Janus kinase 2 (JAK2)-dependent signaling in bovine PE cells. Definitive activation of STAT3, a downstream target for JAK2, was observed in PE cells. Also, pharmacological inhibition of JAK2 decreased (P < 0.05) PE cell numbers.

Conclusions

To conclude, IL6 manipulates ICM development after EPI/PE cell fates are established. The PE cells are the target for IL6, where a JAK-dependent signal is used to regulate PE numbers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12861-020-00235-z.

Technical note: improving the efficiency of generating bovine extraembryonic endoderm cells

The formation of extraembryonic endoderm (XEN) occurs early in embryonic development. The cell types that develop from the XEN remain poorly studied in ruminant species because of the lack of suitable cell culture model systems. The goal of this work was to establish a protocol for producing XEN cell cultures from bovine blastocysts. Previous work identified fibroblast growth factor 2 (FGF2) as a facilitator of bovine XEN development. Further refinements in culture conditions studied here included exposure to 20% fetal bovine serum and FGF2 replenishment. These modifications yielded an endoderm outgrowth formation incidence of 81.6% ± 5.5% compared with 33.3% ± 5.5% in bovine serum albumin (BSA)-supplemented controls. These cells resembled XEN when examined morphologically and contained XEN transcripts (GATA binding protein 4 [GATA4] and GATA binding protein 6 [GATA6]) as well as transcripts present in visceral (BCL2 interacting protein 1 [BNIP1] and vascular endothelial growth factor A [VEGFA]) and parietal (C-X-C motif chemokine receptor 4 [CXCR4], thrombomodulin [THBD], and hematopoietically expressed homeobox [HHEX]) XEN. Two XEN cell lines were maintained for prolonged culture. Both lines continued to proliferate for approximately 6 wk before becoming senescent. These cultures maintained an XEN-like state and continued to express GATA4 and GATA6 until senescence. An increase in the abundance of visceral and parietal XEN transcripts was observed with continued culture, suggesting that these cells either undergo spontaneous differentiation or retain the ability to form various XEN cell types. Stocks of cultured cells exposed to a freeze-thaw procedure possessed similar phenotypic and genotypic behaviors as nonfrozen cells. To conclude, a procedure for efficient production of primary bovine XEN cell cultures was developed. This new protocol may assist researchers in exploring this overlooked cell type for its roles in nutrient supply during embryogenesis.

Vascular Endothelial Growth Factor A and VEGFR-1 Change during Preimplantation in Heifers

Vascular endothelial growth factor A (VEGFA) plays a critical angiogenic role in the endometrium of placentalia during preimplantation. The role of VEGFA and its receptors is not fully characterised in bovine reproduction. We analysed the mRNA expression of VEGFA isoforms 121, 165 and 189, and VEGF receptors 1 and 2 in three experimental settings (A, B and C). We compared intercaruncular endometrium of cyclic to pregnant heifers at Days 12, 15 and 18 post insemination (Day 0), and between Day 15 and Day 18 conceptuses (A). We further compared caruncular versus intercaruncular endometrium at Day 15 (B), and endometrium of heifers carrying embryos originating from somatic cell nuclear transfer (SCNT) versus in vitro fertilisation (IVF) at Day 18 (C). Endometrial VEGFA protein was localised and quantified. Pregnant heifers displayed lower intercaruncular endometrial mRNA expression of VEGFA-121 (p = 0.045) and VEGFA-189 (p = 0.009) as well as lower VEGFA protein abundance (p < 0.001) at Day 15. The VEGFA protein was localised in intercaruncular luminal, glandular epithelium and in tunica muscularis of blood vessels. At Day 15, caruncular endometrium displayed higher VEGFA mRNA expression than intercaruncular endometrium (p < 0.05). Intercaruncular endometrial VEGFA protein at Day 18 was higher in abundance in SCNT than in IVF (p = 0.038). Therefore, during preimplantation in cattle, there may be a need for timely physiological reduction in intercaruncular endometrial VEGFA expression in favour of the caruncular area to facilitate a gradient towards the implantation sites. A higher expression of VEGFA in SCNT may predispose for later placentation abnormalities frequently observed following SCNT.

BOARD INVITED REVIEW: Post-transfer consequences of in vitro-produced embryos in cattle

In vitro embryo production (IVP) in cattle has gained worldwide interest in recent years, but the efficiency of using IVP embryos for calf production is far from optimal. This review will examine the pregnancy retention rates of IVP embryos and explore causes for pregnancy failures. Based on work completed over the past 25 yr, only 27% of cattle receiving IVP embryos will produce a live calf. Approximately 60% of these pregnancies fail during the first 6 wk of gestation. When compared with embryos generated by superovulation, pregnancy rates are 10% to 40% lower for cattle carrying IVP embryos, exemplifying that IVP embryos are consistently less competent than in vivo-generated embryos. Several abnormalities have been observed in the morphology of IVP conceptuses. After transfer, IVP embryos are less likely to undergo conceptus elongation, have reduced embryonic disk diameter, and have compromised yolk sac development. Marginal binucleate cell development, cotyledon development, and placental vascularization have also been documented, and these abnormalities are associated with altered fetal growth trajectories. Additionally, in vitro culture conditions increase the risk of large offspring syndrome. Further work is needed to decipher how the embryo culture environment alters post-transfer embryo development and survival. The risk of these neonatal disorders has been reduced by the use of serum-free synthetic oviductal fluid media formations and culture in low oxygen tension. However, alterations are still evident in IVP oocyte and embryo transcript abundances, timing of embryonic cleavage events and blastulation, incidence of aneuploidy, and embryonic methylation status. The inclusion of oviductal and uterine-derived embryokines in culture media is being examined as one way to improve the competency of IVP embryos. To conclude, the evidence presented herein clearly shows that bovine IVP systems still must be refined to make it an economical technology in cattle production systems. However, the current shortcomings do not negate its current value for certain embryo production needs and for investigating early embryonic development in cattle.