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

Pressing needs and recent advances to enhance production of embryos in vitro in cattle

Embryo transfer in cattle is an increasingly important technique for cattle production. Full attainment of the benefits of the technology will depend on overcoming hurdles to optimal performance using embryos produced in vitro. Given its importance, embryo technology research should become a global research priority for animal reproduction science. Among the goals of that research should be developing methods to increase the proportion of oocytes becoming embryos through optimization of in vitro oocyte maturation and in vitro fertilization, producing an embryo competent to establish and maintain pregnancy after transfer, and increasing recipient fertility through selection, management and pharmacological manipulation. The embryo produced in vitro is susceptible to epigenetic reprogramming and methods should be found to minimize deleterious epigenetic change while altering the developmental program of the resultant calf to increase its health and productivity. There are widening opportunities to rethink the technological basis for much of the current practices for production and transfer of embryos because of explosive advances in fields of bioengineering such as microfluidics, three-dimensional printing of cell culture materials, organoid culture, live-cell imaging, and cryopreservation.

Comparison of pregnancy outcomes between 4th day morula and 5th day blastocyst after embryo transfer: a retrospective cohort study

BACKGROUND

This study was designed to evaluate pregnancy outcomes between morulae transferred on day 4 (D4) and blastocysts transferred on day 5 (D5).

METHODS

From September 2017 to September 2020, 1963 fresh transfer cycles underwent early follicular phase extra-long protocol for assisted conception in our fertility center were divided into D4 (324 cases) and D5 (1639 cases) groups, and the general situation and other differences of patients in both groups were compared. To compare the differences in pregnancy outcomes, the D4 and D5 groups were further divided into groups A and B based on single and double embryo transfers. Furthermore, the cohort was divided into two groups: those with live births (1116 cases) and those without (847 cases), enabling a deeper evaluation of the effects of D4 or D5 transplantation on assisted reproductive outcomes.

RESULTS

In single embryo transfer, there was no significant difference between groups D4A and D5A (P > 0.05). In double embryo transfer, group D4B had a lower newborn birthweight and a larger proportion of low birthweight infants (P < 0.05). The preterm delivery rate, twin delivery rate, cesarean delivery rate, and percentage of low birthweight infants were lower in the D5A group than in the D5B group (P < 0.05). Analysis of factors influencing live birth outcomes further confirmed the absence of a significant difference between D4 and D5 transplantation in achieving live birth (P > 0.05).

CONCLUSION

When factors such as working life and hospital holidays are being considered, D4 morula transfer may be a good alternative to D5 blastocyst transfer. Given the in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) success rate and risk of twin pregnancy, D4 morula transfer requires an adapted decision between single and double embryo transfer, although a single blastocyst transfer is recommended for the D5 transfer in order to decrease the twin pregnancy rate. In addition, age, endometrial thickness and other factors need to be taken into account to personalize the IVF program and optimize pregnancy outcomes.

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.

Transcriptome changes associated with elongation of bovine conceptuses I: Differentially expressed transcripts in the conceptus on day 17 after insemination

The objective was to characterize transcriptome changes associated with elongation in bovine conceptuses during preimplantation stages. Nonlactating Holstein cows were euthanized 17 d after artificial insemination (AI) and the uterine horn ipsilateral to the CL was flushed with saline solution. Recovered conceptuses were classified as small (1.2 to 6.9 cm; n = 9), medium (10.5 to 16.0 cm; n = 9), or large (18.0 to 26.4 cm; n = 10). Total mRNA was extracted and subjected to transcriptome analyses using the Affymetrix Gene Chip Bovine array. Data were normalized using the GCRMA method and analyzed by robust regression using the Linear Models for Microarray library within Bioconductor in R. Transcripts with P ≤ 0.05 after adjustment for false discovery rate and fold change ≥1.5 were considered differentially expressed. Functional analyses were conducted using the Ingenuity Pathway Analysis platform. Comparisons between large versus small (LvsS), large versus medium (LvsM), and medium versus small (MvsS) conceptuses yielded a total of 634, 240, and 63 differentially expressed transcripts, respectively. Top canonical pathways of known involvement with embryo growth that were upregulated in large conceptuses included actin cytoskeleton (LvsS), integrin signaling (LvsS and LvsM), ephrin receptor (LvsS), mesenchymal transition by growth factor (LvsM), and regulation of calpain protease (LvsS). Transcripts involved with lipid metabolism pathways (LXR/RXR, FXR/RXR, hepatic fibrosis) were associated with the LvsS and LvsM, and some transcripts such as APOC2, APOH, APOM, RARA, RBP4, and PPARGC1A, were involved in these pathways. An overall network summary associated biological downstream effects of invasion of cells, proliferation of embryonic cells, and inhibition of organismal death in the LvsS. In conclusion, differently expressed transcripts in the LvsS comparison were associated with the cell growth, adhesion, and organismal development, although part of these findings could be attributed to differences in circulatory concentrations of progesterone of the cows that bore large and small conceptuses. The large and medium conceptuses developed under similar concentrations of progesterone and presented 240 differently expressed transcripts, associated with cell differentiation, metabolite regulation, and other biological processes.

Transcriptomic profiling of the bovine endosalpinx and endometrium to identify putative embryokines

The objectives of the present study were to characterize the expression of genes encoding for cell signaling ligands in the bovine endosalpinx and endometrium and analyze spatial changes in gene expression. RNA sequencing was performed for the endosalpinx from the ampulla of the oviduct and endometrium from the upper and middle uterine horn and uterine body at day 2 after ovulation from ipsilateral and contralateral sides relative to the ovulatory ovary. Of the 17,827 unique mRNA transcripts mapped, 2,072 were affected by cranial-caudal position in the reproductive tract and 818 were affected by side (false discovery rate < 0.05). There were 334 genes encoding for cell signaling ligands, with 128 genes having greater than two transcripts per million on average. A total of 81 cell signaling ligand genes were affected by position and 24 were affected by side. A data set of the transcriptome of two to four cell embryos was used to identify cell signaling ligand genes that were highly expressed in the ampulla for which there was high expression of the receptor in the embryo. The most expressed ligand-receptor pairs were PSAP/SORT1, MIF/CXCR4, GPI/AMFR, and KITLG/KIT. These cell signaling ligands, as well as others whose gene is expressed in the endosalpinx and endometrium, may influence early embryonic development. Spatial changes throughout the reproductive tract highlight the distinctive expression profile of the oviduct versus the endometrium, including a set of the identified genes encoding for cell signaling ligands, and highlight the local influence of the ovary. The results also show the continuity of expression for large numbers of genes in the reproductive tract.NEW & NOTEWORTHY Examination of the transcriptome of the endosalpinx and endometrium revealed the degree to which gene expression in the reproductive tract varies spatially. The expression of genes encoding cell signaling molecules that could potentially regulate embryonic development was also identified.

Presence of KREMEN receptors for DKK1 in the preimplantation bovine embryo

The WNT inhibitory protein DKK1 has been shown to regulate development of the preimplantation embryo to the blastocyst stage. In cattle, DKK1 increases the number of trophectoderm cells that are the precursor of the placenta. DKK1 can affect cells by blocking WNT signaling through its receptors KREMEN1 and KREMEN2. Here it was shown that the mRNA for KREMEN1 and KREMEN2 decline as the embryo advances in development. Nonetheless, immunoreactive KREMEN1 was identified in blastocysts using Western blotting. DKK1 also decreased amount of immunoreactive CTNNB1 in blastocysts, as would be expected if DKK1 was signaling through a KREMEN-mediated pathway. Thus, it is likely that KREMEN1 functions as a receptor for DKK1 in the preimplantation bovine embryo.

Review: The putative role of Progesterone Receptor membrane Component 1 in bovine oocyte development and competence

Acquisition of developmental competence is a complex process in which many cell types cooperate to support oocyte maturation, fertilisation, and preimplantation embryonic development. In recent years, compelling evidence has shown that Progesterone Receptor Membra Component 1 (PGRMC1) is expressed in many cell types of the mammalian reproductive system where it exerts diverse functions. In the ovary, PGRMC1 affects follicular growth by controlling cell viability and proliferation of granulosa cells. PGRMC1 has also a direct role in promoting a proper completion of bovine oocyte maturation, as altering its function leads to defective chromosome segregation and polar body extrusion. Strikingly, the mechanism by which PGRMC1 controls mitotic and meiotic cell division seems to be conserved, involving an association with the spindle apparatus and the chromosomal passenger complex through Aurora kinase B. Conclusive data on a possible role of PGRMC1 in the preimplantation embryo are lacking and further research is needed to test whether the mechanisms that are set in place in mitotic cells also govern blastomere cleavage and subsequent differentiation. Finally, PGRMC1 is also expressed in oviductal cells and, as such, it might also impact fertilisation and early embryonic development, although this issue is completely unexplored. However, the study of PGRMC1 function in the mammalian reproductive system remains a complex matter, due to its pleiotropic function.

Review: Some challenges and unrealized opportunities toward widespread use of the in vitro-produced embryo in cattle production

The embryo produced by in vitro oocyte maturation, fertilization, and embryonic development is an important resource for genetic improvement and has the potential to improve female fertility and to be programmed to produce offspring with superior ability for health and production. The cultured embryo is also an important component of several realized and potential technologies such as gene editing, somatic cell nuclear cloning, stem cell technologies and gamete generation in vitro. Full realization of the opportunities afforded by the in vitro-produced embryo will require overcoming some technical obstacles to cost-effective implementation of an embryo transfer program. Among the research goals for improving the penetration of embryo transfer in the cattle industry are development of methods to increase the supply of oocytes from genetically elite females, enhance the proportion of oocytes that become transferrable embryos, improve the fraction of embryos that establish pregnancy after transfer, reduce pregnancy wastage after pregnancy diagnosis, and identify culture conditions to optimize postnatal phenotype.

Actions of WNT family member 5A to regulate characteristics of development of the bovine preimplantation embryo†

WNT signaling is important for regulation of embryonic development. The most abundant WNT gene expressed in the bovine endometrium during the preimplantation period is WNT5A. One objective was to determine whether WNT5A regulates competence of the bovine preimplantation embryo to become a blastocyst and alters the number of cells in the inner cell mass and trophectoderm. A second objective was to delineate features of the cell-signaling mechanisms involved in WNT5A actions. WNT5A caused a concentration-dependent increase in the proportion of embryos developing to the blastocyst stage and in the number of inner cell mass cells in the resultant blastocysts. A concentration of 200 ng/mL was most effective, and a higher concentration of 400 ng/mL was not stimulatory. Bovine serum albumin in culture reduced the magnitude of effects of WNT5A on development to the blastocyst stage. WNT5A affected expression of 173 genes at the morula stage; all were upregulated by WNT5A. Many of the upregulated genes were associated with cell signaling. Actions of WNT5A on development to the blastocyst stage were suppressed by a Rho-associated coiled-coil kinase (ROCK) signaling inhibitor, suggesting that WNT5A acts through Ras homology gene family member A (RhoA)/ROCK signaling. Other experiments indicated that actions of WNT5A are independent of the canonical β-catenin signaling pathway and RAC1/c-Jun N-terminal kinase (JNK) signaling. This is the first report outlining the actions of WNT5A to alter the development of the mammalian embryo. These findings provide insights into how embryokines regulate maternal-embryonic communication.

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.