Inhibition of FGF Signalling Pathway Augments the Expression of Pluripotency and Trophoblast Lineage Marker Genes in Porcine Parthenogenetic Blastocyst

PS48 promotes in vitro maturation and developmental competence of porcine oocytes through activating PI3K/Akt signalling pathway

Oocyte maturation plays a vitally important role in porcine reproduction. Regrettably, the quality of oocytes matured in vitro is weaker than that of in vivo matured oocytes. We collected and cultivated porcine cumulus oocyte complexes (COCs) in vitro with phosphoinositide-dependent kinase 1 (PDK1) activator 5-(4-chloro-phenyl)-3-phenyl-pent-2-enoic acid (PS48), whose concentrations were 0, 2, 5, 10 and 20 µM to investigate whether the phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) signalling pathway would impact the oocyte quality. The results showed that 10 µM PS48 increased the oocyte proportion of metaphase II (MII) stage and improved the expansion of cumulus cells (CCs). What's more, the activation of PI3K/Akt signalling pathway could regulate the expression of maturation-related genes and proteins. The results of quantitative real-time PCR showed that 10 µM PS48 increased the mRNA and protein levels of Akt and regulated maturation-related genes, including cyclin B1, MOS, BMP15, GDF9, CDC2, mTOR, BAX, BCL2 and caspase-3. The results of Western blot indicated that 10µM PS48 increased the protein abundance of Akt, phosphorylation of Akt Thr308 (p-Akt^Thr308 ) and cyclin B1, but decreased the protein abundance of pro-apoptotic BAX. These results suggested that adding 10 µM PS48 to mature culture medium could promote the maturation of porcine oocytes, potentially through activating the PI3K/Akt signalling pathway.

PI3K inhibitor reduces in vitro maturation and developmental competence of porcine oocytes

The phosphatidylinositol -3- kinase (PI3K) signaling pathway is critical for the cell proliferation, apoptosis, metabolism, DNA repair and protein synthesis. Significant effort has focused on elucidating the relationship between PI3K signaling pathway and other nuclear signal transducers; However, little is known about the connection between PI3K signaling pathway and porcine oocyte meiotic maturation. In this study, we investigated the function of PI3K signaling pathway in porcine oocytes. PI3K signaling pathway was important during oocyte maturation. Furthermore, the PI3K signaling pathway inhibitor LY-294002 blocked porcine oocyte maturation, reducing the percentage of oocytes that first polar body (PBI) extrusion. LY-294002 also decreased the expression of oocyte proliferation-related gene PCNA and reduced the mRNA and protein levels of PI3K. What's more, LY-294002 also decreased other maturation-related genes that are predominantly expressed duringporcine oocyte maturation, including bone morphogenetic protein 15 (BPM15), growth differentiation factor 9 (GDF9), cell division cycle protein 2 (CDC2), phosphatase and tensin homolog (PTEN), CyclinB1, MOS and Akt. LY-294002 treatment decreased the developmental potential of blastocysts following parthenogenetic activation, increased the level of cell apoptosis and reduced the level of cell-cycle. This study revealed that inhibiting the PI3K signaling pathway could reduce in vitro maturation and developmental competence of porcine oocytes, probably by reducing cell cycle arrest and proliferation, promoting the oocyte apoptosis, and altering the expression of other maternal genes.

Early development of porcine parthenogenetic embryos and reduced expression of primed pluripotent marker genes under the effect of lysophosphatidic acid

To further promote the early development of porcine embryos and capture "naïve" pluripotent state within blastocyst, the experiment explored the effects of lysophosphatidic acid (LPA) on the early development of porcine parthenogenetic embryos and the expression of pluripotency relevant genes. The results showed that the addition of 50 μM LPA significantly improved parthenogenetic embryo cleavage rate (82.7% vs. 74.7%, p < 0.05), blastocyst rate (24.5% vs. 11.3%, p < 0.05) and blastocyst cell count (56 ± 7.9 vs. 42 ± 1.0, p < 0.05) than that of the control group. In addition, immunostaining experiment determined that the fluorescence intensity of OCT4 was also significantly higher than that of the control group. The quantitative real-time polymerase chain reaction (qRT-PCR) test revealed that addition of 50 μM LPA could significantly enhance the expression level of pluripotent gene OCT4 and trophoblast marker genes CDX2, however, decrease the expression of primitive hypoblast marker gene GATA4. The results also indicated that LPA might decrease the expression of GATA4 through the ROCK signalling pathway. For further investigating the effect of the addition of LPA on the expression of "primed" and "naïve" genes, we also detected the expression of those pluripotency-related genes by qRT-PCR. The results showed addition of LPA had no significant effect on the expression of "naïve" pluripotent genes, but it was able to significantly decrease the expression of "primed" pluripotent genes, NODAL and Activin-A; furthermore, it also could significantly improve the expression of OCT4 and c-Myc which act as two important ES cell renewal factors. Above all, the addition of LPA can facilitate the early development of porcine parthenogenetic embryos, which may be able to benefit for capturing "naïve" pluripotency in vitro through inhibiting "primed" pluripotency.

Pre-implantation Development of Domestic Animals

During the first days following fertilization, cells of mammalian embryo gradually lose totipotency, acquiring distinct identity. The first three lineages specified in the mammalian embryo are pluripotent epiblast, which later gives rise to the embryo proper, and two extraembryonic lineages, hypoblast (also known as primitive endoderm) and trophectoderm, which form tissues supporting development of the fetus in utero. Most of our knowledge regarding the mechanisms of early lineage specification in mammals comes from studies in the mouse. However, the growing body of evidence points to both similarities and species-specific differences. Understanding molecular and cellular mechanisms of early embryonic development in nonrodent mammals expands our understanding of basic mechanisms of differentiation and is essential for the development of effective protocols for assisted reproduction in agriculture, veterinary medicine, and for biomedical research. This review summarizes the current state of knowledge on key events in epiblast, hypoblast, and trophoblast differentiation in domestic mammals.