Influence of the preimplantation embryo development (Ped) gene on embryonic platelet-activating factor (PAF) levels

Differential expression of tsRNAs and miRNAs in embryo culture medium: potential impact on embryo implantation

PURPOSE

Can small RNA derived from embryos in conditioned embryo culture medium (ECM) influence embryo implantation?

METHODS

We employed small RNA sequencing to investigate the expression profiles of transfer RNA-derived small RNA (tsRNA) and microRNA (miRNA) in ECM from high-quality and low-quality embryos. Quantitative real-time PCR was employed to validate the findings of small RNA sequencing. Additionally, we conducted bioinformatics analysis to predict the potential functions of these small RNAs in embryo implantation. To establish the role of tiRNA-1:35-Leu-TAG-2 in embryonic trophoblast cell adhesion, we utilized co-culture systems involving JAR and Ishikawa cells.

RESULTS

Our analysis revealed upregulation of nine tsRNAs and four miRNAs in ECM derived from high-quality embryos, whereas 37 tsRNAs and 12 miRNAs exhibited upregulation in ECM from low-quality embryos. The bioinformatics analysis of tsRNA, miRNA, and mRNA pathways indicated that their respective target genes may play pivotal roles in both embryo development and endometrial receptivity. Utilizing tiRNA mimics, we demonstrated that the prominently expressed tiRNA-1:35-Leu-TAG-2 in the low-quality ECM group can be internalized by Ishikawa cells. Notably, transfection of tiRNA-1:35-Leu-TAG-2 into Ishikawa cells reduced the attachment rate of JAR spheroids.

CONCLUSION

Our investigation uncovers significant variation in the expression profiles of tsRNAs and miRNAs between ECM derived from high- and low-quality embryos. Intriguingly, the release of tiRNA-1:35-Leu-TAG-2 by low-quality embryos detrimentally affects embryo implantation and endometrial receptivity. These findings provide fresh insights into understanding the molecular foundations of embryo-endometrial communication.

Genes and pathways associated with pregnancy loss in dairy cattle

Pregnancy loss directly impairs reproductive performance in dairy cattle. Here, we investigated genetic factors associated with pregnancy loss following detection of a viable embryo around 42 days of gestation. The objectives of this study were to perform whole-genome scans and subsequent gene-set analyses for identifying candidate genes, functional gene-sets and gene signaling pathways implicated in pregnancy loss in US Holstein cows. Data consisted of about 58,000 pregnancy/abortion records distributed over nulliparous, primiparous, and multiparous cows. Threshold models were used to assess the binary response of pregnancy loss. Whole‐genome scans identified at least seven genomic regions on BTA2, BTA10, BTA14, BTA16, BTA21, BTA24 and BTA29 associated with pregnancy loss in heifers and lactating cows. These regions harbor several candidate genes that are directly implicated in pregnancy maintenance and fetal growth, such as CHST14, IGF1R, IGF2, PSEN2, SLC2A5 and WNT4. Moreover, the enrichment analysis revealed at least seven significantly enriched processes, containing genes associated with pregnancy loss, including calcium signaling, cell–cell attachment, cellular proliferation, fetal development, immunity, membrane permeability, and steroid metabolism. Additionally, the pathway analysis revealed a number of significant gene signaling pathways that regulate placental development and fetal growth, including Wnt, Hedgehog, Notch, MAPK, Hippo, mTOR and TGFβ pathways. Overall, our findings contribute to a better understanding of the genetic and biological basis of pregnancy loss in dairy cattle and points out novel strategies for improving pregnancy maintenance via marker‐assisted breeding.

Systematic analysis of the factors that adversely affect the rate of cell accumulation in mouse embryos during their culture in vitro

BACKGROUND

Retarded embryo growth is a pervasive effect of culture in vitro.

METHODS

A systematic analysis of the interactions between media design, embryo culture density, oxygen tension, amino acids, trophic ligands and the genetic background of the mouse on embryo growth rates in vitro was performed.

RESULTS

Growth retardation of mouse zygotes was greater in 20% O2 than 5%, a sequential media design was superior to static simple media designs, but the supplementation of simple media with mixed amino acids mitigated this difference. There was a beneficial effect of communal culture in small volumes, and supplementation with a trophic ligand (Paf) further enhanced growth rates. For hybrid strain zygotes (B6CBF1) communal culture in KSOM media supplemented with amino acids, albumin and Paf under 5% O₂ resulted in complete rescue of their rate of accumulation of cells and blastocyst formation. Inbred strain (C57BL6/J) zygotes, however, still showed some retardation of development under these conditions. The additional supplementation of media with another trophic ligand (IGF1) showed a further additive beneficial effect on development of inbred strain embryos but they still showed a growth deficit of ~ 23% cell number. The results show that optimising the interactions between a range of culture conditions and media design can rescue hybrid strain embryos from a retarded rate of cell proliferation caused by culture in vitro, but this was incomplete for the B6 strain.

CONCLUSIONS

The results indicate that the growth requirement of embryos in vitro varies depending upon their genetic background and provide models for the further genetic analysis of embryo growth.

Culture systems: embryo density

Embryo density is defined as the embryo-to-volume ratio achieved during in vitro culture; in other words, it is the number of embryos in a defined volume of culture medium. The same density can be achieved by manipulating either the number of embryos in a given volume of medium, or manipulating the volume of the medium for a given number of embryos: for example, a microdrop with five embryos in a 50 μl volume under oil has the same embryo-to-volume ratio (1:10 μl) as a microdrop with one embryo in a 10 μl volume under oil (1:10 μl). Increased embryo density can improve mammalian embryo development in vitro; however, the mechanism(s) responsible for this effect may be different with respect to which method is used to increase embryo density.Standard, flat sterile plastic petri dishes are the most common, traditional platform for embryo culture. Microdrops under a mineral oil overlay can be prepared to control embryo density, but it is critical that dish preparation is consistent, where appropriate techniques are applied to prevent microdrop dehydration during preparation, and results of any data collection are reliable, and repeatable. There are newer dishes available from several manufacturers that are specifically designed for embryo culture; most are readily available for use with human embryos. The concept behind these newer dishes relies on fabrication of conical and smaller volume wells into the dish design, so that embryos rest at the lowest point in the wells, and where putative embryotrophic factors may concentrate.Embryo density is not usually considered by the embryologist as a technique in and of itself; rather, the decision to culture embryos in groups or individually is protocol-driven, and is based more on convenience or the need to collect data on individual embryos. Embryo density can be controlled, and as such, it can be utilized as a simple, yet effective tool to improve in vitro development of human embryos.

MicroRNA expression in preimplantation mouse embryos from Ped gene positive compared to Ped gene negative mice

PURPOSE

The mouse preimplantation embryo development (Ped) gene product, Qa-2, influences the rate of preimplantation embryonic development and overall reproductive success. Here we investigated the expression pattern of two microRNAs, miR-125a and miR-125b, known to be involved in development in lower organisms, in preimplantation embryos from the two-cell, four-cell, eight-cell, morula, and blastocyst stages of development from the congenic B6.K1 (Ped negative) and B6.K2 (Ped positive) strains of mice.

METHOD

B6.K1 and B6.K2 congenic mice differ only in the absence (B6.K1) or presence (B6.K2) of the genes encoding Qa-2 protein. We analyzed the expression of miR-125a and miR-125b in B6.K1 and B6.K2 preimplantation embryos by using real-time PCR.

RESULT

We found no variability in miR-125b expression at any developmental stage in both strains. However, miR-125a expression increased during development in both strains and was ten times higher in Ped negative (B6.K1) embryos than in Ped positive (B6.K2) embryos by the blastocyst stage of development.

CONCLUSION

Our results show that the absence of the Ped gene profoundly affects the level of a miRNA (miR-125a) known to regulate early development. The implication is that miR-125a is likely involved in the regulation of timing of early development in mice.

Preimplantation embryo development (Ped) gene copy number varies from 0 to 85 in a population of wild mice identified as Mus musculus domesticus

The preimplantation embryo development (Ped) gene regulates the rate of preimplantation embryonic cleavage division and subsequent embryo survival. In the mouse, the Ped gene product is Qa-2 protein, a nonclassical MHC class I molecule encoded by four tandem genes, Q6/Q7/Q8/Q9. Most inbred strains of mice have all four genes on each allelic chromosome, making a total of eight Qa-2 encoding genes, but there are a few strains that are missing all eight genes, defining a null allele. Mouse strains with the presence of the Qa-2 encoding genes express Qa-2 protein and produce embryos with a faster rate of preimplantation embryonic development and a greater chance of embryo survival compared to mouse strains with the null allele. There is extensive evidence that the human homolog of Qa-2 is HLA-G. HLA-G in humans, like Qa-2 in mice, is associated with enhanced reproductive success. The human population is an outbred population. Therefore, for a better comparison to the human population, we undertook an investigation of the presence of the genes encoding Qa-2 in an outbred population of mice. We used Real-Time Quantitative PCR to quantify the number of Qa-2 encoding genes in a population of 32 wild mice identified as Mus musculus domesticus both by morphologic assessment and by PCR analysis of their DNA. We found great variability in the number of Qa-2 encoding genes in the wild mice tested. The wild mouse with the highest number of Qa-2 encoding genes had 85 such genes, whereas we discovered one wild mouse without any Qa-2 encoding genes. Evolutionary implications of a range of Qa-2 encoding gene numbers in the wild mouse population are discussed, as well as the relevance of our findings to humans.

Activation of T cells by cross-linking Qa-2, the ped gene product, requires Fyn

PROBLEM

Qa-2, the product of the Ped (preimplantation development) gene, regulates the rate of cell division of preimplantation mouse embryos by an unknown mechanism. Due to the limited availability of preimplantation embryos, T cells were used as a model system to assess the possible roles of Fyn and Lck, and two downstream effectors, PI-3 kinase and Akt, in Qa-2 induced cell proliferation.

METHOD OF STUDY

Resting T cells were stimulated to proliferate by treating with mouse anti-Qa-2 antibody, cross-linking with anti-mouse immunoglobulin, and adding PMA. The effects of kinase inhibitors on this proliferation were studied. Co-immunoprecipitates of T-cell lysates were analyzed for possible associations between Qa-2 and Fyn or Lck. Fyn knockout mice (Fyn-/-) were used to determine whether Fyn is required for T-cell activation induced by cross-linking Qa-2.

RESULTS

An inhibitor of Src family kinases and inhibitors of PI-3 kinase and Akt suppressed proliferation of resting T cells induced by cross-linking Qa-2. Fyn, but not Lck, co-immunoprecipitated with Qa-2. Fyn-/- T cells failed to proliferate in response to Qa-2 cross-linking.

CONCLUSION

Fyn, PI-3 kinase, and Akt are required for the activation of T cells by cross-linking Qa-2.

Two high-fertility mouse lines show differences in component fertility traits after long-term selection

Two selected high-fertility mouse lines, namely FL1 and FL2, and a non-selected control (Fzt:DU), all derived from the same genetic pool, were analysed as an animal model for polytocous species to elucidate the effects of long-term selection and to identify relevant component traits that may be responsible for fertility performance. The index trait used for breeding selection was largely increased by 104% and 142% in the FL1 and FL2 lines, respectively, resulting in an average litter size of 17.3 pups and 18.7 pups per litter in the FL1 and FL2 lines, respectively, compared with a litter size of 11.0 pups per litter in the control (Fzt:DU). In addition, different component fertility traits were analysed in females of all three lines at different stages of the oestrous cycle and pregnancy. In conclusion: (1) early embryonic development was accelerated in the FL1 and FL2 lines compared with control; (2) plasma progesterone levels were not correlated with fertility performance; (3) a largely increased ovulation number (i.e. number of corpora lutea) was responsible for high prolificacy in both lines; however, (4) the number of ova shed, as well as the rate of loss of ova and pre- and postimplantation conceptuses, was very different in the FL1 and FL2 lines, suggesting that different genetic components may be responsible for the high prolificacy in both high-fertility lines.