Molecular characterization of the follicular development of BMP15-edited pigs.

In brief: The regulatory role of BMP15 on porcine ovarian follicular development still remains unclear. This study reveals that biallelic editing of BMP15 impairs SMAD signaling and inhibits granulosa cell proliferation, resulting in porcine follicular development arrest and ovarian hypoplasia. Abstract: Bone morphogenetic protein 15 (BMP15) is a member of the transforming growth factor beta (TGF-ß) superfamily, which is critical for facilitating ovarian folliculogenesis in mono-ovulatory mammalian species but is not essential in polyovulatory mice. Our previously established BMP15-edited pigs presented varied female reproductive phenotypes, suggesting the important role of BMP15 in ovarian folliculogenesis in polyovulatory pigs. To understand the regulatory mechanism underlying the effect of BMP15 on porcine ovarian follicular development, we molecularly characterized infertile biallelic-BMP15-edited gilts with ovarian hypoplasia. We found that an absence of BMP15 proteins in biallelic-BMP15-edited gilts can lead to premature activation of primordial follicles, possibly through the upregulation of KITLG-KIT-PI3K-AKT signaling pathways. However, this absence severely impaired SMAD (Sma and Mad proteins from Caenorhabditis elegans and Drosophila, respectively) signaling, causing severely reduced granulosa cell proliferation, leading to the arrest of follicular development during the preantral stage and ovarian hypoplasia, resulting in complete infertility. Our study expands the understanding of the molecular functions of BMP15 in nonrodent polyovulatory mammals.

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-AktThr308 ) 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.

The key long non-coding RNA screening and validation between germinal vesicle and metaphase II of porcine oocyte in vitro maturation.

Oocyte maturation plays a vitally important role in the reproduction of pigs. However, the roles of messenger RNAs (mRNAs) and long non-coding RNAs (lncRNAs) in the developmental process of porcine oocyte maturation are still largely unclear. In this study, a transcriptome analysis of germinal vesicle (GV) and metaphase II (MII) of oocytes from Chinese Duroc pigs was performed. A total of 1,753,030 and 2,486 differentially expressed (DE) mRNAs, 22,811 and 9,868 DE lncRNAs were identified between GV and MII stages, respectively. Furthermore, functional enrichment analysis showed that the common DE mRNAs and DE lncRNAs during the process of maturation were mainly involved in biological process and cellular components. Our study provides new insights of the expression changes of mRNAs and lncRNAs during GV and MII stages, which might contribute to the maturation of oocytes. These results greatly improve our understanding of the molecular mechanisms regulating the maturation of oocytes in pigs.

Bone morphogenetic protein 15 gene disruption affects the in vitro maturation of porcine oocytes by impairing spindle assembly and organelle function.

Bone morphogenetic protein 15 (BMP15) plays a crucial role in the porcine follicular development. However, its exact functions in the in vitro maturation (IVM) of porcine oocytes remain largely unknown. Here, through cytoplasmic injection of a preassembled crRNA-tracrRNA-Cas9 ribonucleoprotein complex, we achieved BMP15 disruption in approximately 54 % of the cultured porcine oocytes. Editing BMP15 impaired the IVM of porcine oocytes, as indicated by the significantly increased abnormal spindle assembly and reduced first polar body (PB1) extrusion. The editing also impaired cytoplasmic maturation of porcine oocytes, as reflected by reduced abundant of Golgi apparatus and impaired functions of mitochondria. The impaired IVM of porcine oocytes by editing BMP15 possibly was associated with the attenuated SMAD1/5 and EGFR-ERK1/2 signaling in the cumulus granulosa cells (CGCs) and the inhibited MOS/ERK1/2 signaling in oocytes. The attenuated MOS/ERK1/2 signaling may contribute to the inactivation of maturation promoting factor (MPF) and the increased abnormal spindle assembly, leading to reduced PB1 extrusion. It also may contribute to reduced Golgi apparatus formation, and impaired functions of mitochondria. These findings expand our understanding of the regulatory role of BMP15 in the IVM of porcine oocytes and provide a basis for manipulation of porcine reproductive performance.

Efficient editing BMP15 in porcine oocytes through microinjection of CRISPR ctRNP.

Bone morphogenetic protein 15 (BMP15) is an X-linked gene encoding an oocyte secreted factor, which plays varied functions in the female fertility between mono-ovulatory and poly-ovulatory mammalian species. We previously found that knockout of BMP15 completely blocked porcine follicular development at preantral stages. However, the specific function of BMP15 on porcine oocytes in vitro maturation remains largely unknown. Here, we injected the pre-assembled crRNA + tracrRNA + Cas9 ribonucleoprotein (ctRNP) complex into the cytoplasm of germinal vesicle stage porcine oocytes to disrupt BMP15. The ctRNP composed of Cas9 nuclease and crRNA-tracrRNA complex at 1.2/1 content ratio. The tested crRNA-tracrRNA complex concentration ranging from 50 to 200 ng/µL, all presented effective editing of BMP15 in porcine oocytes, and the 125 ng/µL crRNA-tracrRNA complex presented the highest editing efficiency (39.23 ± 3.33%). Surprisingly, we found approximately 95% edited oocytes presented monoallelic mutations, and only 5% edited oocytes harbored biallelic mutations. Interestingly, the coinjected two crRNAs guided the ctRNP complex to concurrently cut within a 10 bp window of the PAM (protospacer adjacent motif), resulting in a precise deletion within BMP15 in 85.9% edited oocytes, and additional deletion happened in 14.1% edited oocytes, which resulted in large fragment deletions in BMP15. Most deletions caused frameshift and introduced premature stop codon in BMP15, resulting in the disruption of BMP15 protein expression, which was confirmed by the Western blot analysis showing the reduced BMP15 protein expression in ctRNP injected oocytes. The disruption of BMP15 attenuated the activation of SMAD1/5/8 signaling, and impaired cumulus expansion of porcine cumulus cell-oocyte complexes (COCs). Our study proved that delivering CRISPR ctRNP into porcine oocytes by microinjection was able to edit BMP15 efficiently, providing a new strategy to investigate the functions of oocyte-specific secreted factors in oocyte in vitro maturation.

Quercetin protects porcine oocytes from in vitro aging by reducing oxidative stress and maintaining the mitochondrial functions.

Quercetin (QUE) is a component of the flavonoid family that shows various therapeutic properties, such as antioxidant effects. However, whether QUE affects porcine oocyte in vitro aging has not yet been investigated. Therefore, in this study, we applied various doses of QUE to freshly isolated porcine oocytes and found that 10 µM QUE improved the oocyte maturation rate in vitro, as reflected by the increased degree of cumulus cell expansion and first polar body extrusion. More importantly, we found that QUE reduced in vitro aging and improved the maturity level of porcine oocytes after another 24 h of culturing, accompanied by the upregulated expression levels of bone morphogenetic protein 15, growth differentiation factor 9, Moloney sarcoma oncogene, and cyclin-dependent kinase 2. In addition, we found that QUE treatment significantly reduced the intracellular reactive oxygen species levels, apoptosis, and autophagy and upregulated the expression levels of superoxide dismutase 2 and catalase in aged porcine oocytes. In addition, QUE restored impaired mitochondrial membrane potential and spindle assembly in aged porcine oocytes. Our findings demonstrate that QUE can protect porcine oocytes from in vitro aging by reducing oxidative stress and maintaining mitochondrial function.

Restoring mammary gland structures and functions with autogenous cell therapy.

In somatic cell reprogramming, cells must escape the somatic cell-specific gene expression program to adopt other cell fates. Here, in vitro chemical induction with RepSox generated chemically induced mammary epithelial cells (CiMECs) with milk secreting functions from goat ear fibroblasts (GEFs). Transplanted CiMECs regenerated the normal mammary gland structure with milk-secreting functions in nude mice. Single-cell RNA sequencing revealed that during the reprogramming process, GEFs may sequentially undergo embryonic ectoderm (EE)-like and different MEC developmental states and finally achieve milk secreting functions, bypassing the pluripotent state. Mechanistically, Smad3 upregulation induced by transforming growth factor ß (TGFß) receptor 1 (TGFßR1) downregulation led to GEF reprogramming into CiMECs without other reprogramming factors. The TGFßR1-Smad3 regulatory effects will provide new insight into the TGFß signaling pathway regulation of somatic cell reprogramming. These findings suggest an innovative strategy for autogenous cell therapy for mammary gland defects and the production of transgenic mammary gland bioreactors.

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.