Effect of sex differences in donor foetal fibroblast on the early development and DNA methylation status of buffalo (Bubalus bubalis) nuclear transfer embryos

Perspectives in Genome-Editing Techniques for Livestock

Genome editing of farm animals has undeniable practical applications. It helps to improve production traits, enhances the economic value of livestock, and increases disease resistance. Gene-modified animals are also used for biomedical research and drug production and demonstrate the potential to be used as xenograft donors for humans. The recent discovery of site-specific nucleases that allow precision genome editing of a single-cell embryo (or embryonic stem cells) and the development of new embryological delivery manipulations have revolutionized the transgenesis field. These relatively new approaches have already proven to be efficient and reliable for genome engineering and have wide potential for use in agriculture. A number of advanced methodologies have been tested in laboratory models and might be considered for application in livestock animals. At the same time, these methods must meet the requirements of safety, efficiency and availability of their application for a wide range of farm animals. This review aims at covering a brief history of livestock animal genome engineering and outlines possible future directions to design optimal and cost-effective tools for transgenesis in farm species.

Insufficient pyruvate in culture medium arrests mouse embryos at the first cleavage stage associated with abnormal epigenetic modifications

Energy is essential for early embryogenesis, and fertilized eggs can successfully develop to blastocyst in in vitro culture medium with an appropriate energy supply. Conversely, embryonic development is negatively affected by a suboptimal energy supply. We previously observed that a low level of pyruvate greatly arrests mouse embryos at the 2-cell stage. However, how methylation modifications are affected at this specific stage remains unknown. In this study, we found that mouse embryos could timely develop to the 4-cell stage in K⁺simplex optimized medium (KSOM) with control level of pyruvate, but embryos were significantly arrested at the 2-cell stage when pyruvate was reduced to 0.2-fold of the control level. Moreover, the fluorescence intensities of 5 mC, H3K4me2, H3K9me2 and H3K27me2 in the 2-cell stage embryos of the 0.2-fold pyruvate group were notedly lower than those of the control group, but N6-methyladenosine (m⁶A) fluorescence intensity was higher, suggesting that global genomic DNA, histone and m⁶A methylation modifications are disrupted with low levels of pyruvate. Consistently, the mRNA levels of genes related to DNA methylation, histone methylation and m⁶A modifications were also disturbed in the 2-cell stage embryos cultured with low levels of pyruvate. In summary, our findings demonstrate that insufficient pyruvate in culture medium results in mouse embryonic developmental arrest, at least in part due to defects in methylation modifications.

Establishment and characterization of fibroblast cultures derived from a female common hippopotamus (Hippopotamus amphibius) skin biopsy

The population decline of the common hippopotamus (Hippopotamus amphibius) has necessitated the preservation of their genetic resources for species conservation and research. Of all actions, cryopreservation of fibroblast cell cultures derived from an animal biopsy is considered a simple but efficient means. Nevertheless, preserving viable cell cultures of the common hippopotamus has not been achieved to our knowledge. To this end, we established and characterized fibroblast cell cultures from the skin sample of a newborn common hippopotamus in this study. By combining the tissue explant direct culture and enzymatic digestion methods, we isolated a great number of cells with typical fibroblastic morphology and high viability. Neither bacteria/fungi nor mycoplasma was detectable in the cell cultures throughout the study. The population doubling time was 34 h according to the growth curve. Karyotyping based on Giemsa staining showed that the cultured cells were diploid with 36 chromosomes in all, one pair of which was sex chromosomes. The amplified mitochondrial cytochrome C oxidase subunit I gene sequence of the cultured cells was 99.26% identical with that of the registered H. amphibius complete mitochondrial DNA, confirming the species of origin of the cells. Flow cytometry and immunofluorescence staining results revealed that the detected cells were positive for fibroblast markers, S100A4, and vimentin. In conclusion, we generated the fibroblast cell cultures from a common hippopotamus and identified their characteristics using multiple techniques. We believe the cryopreserved cells could be useful genetic materials for future research.

Histone Demethylase KDM4D Could Improve the Developmental Competence of Buffalo (Bubalus Bubalis) Somatic Cell Nuclear Transfer (SCNT) Embryos

Somatic cell nuclear transfer (SCNT) holds vast potential in agriculture. However, its applications are still limited by its low efficiency. Histone 3 lysine 9 trimethylation (H3K9me3) was identified as an epigenetic barrier for this. Histone demethylase KDM4D could regulate the level of H3K9me3. However, its effects on buffalo SCNT embryos are still unclear. Thus, we performed this study to explore the effects and underlying mechanism of KDM4D on buffalo SCNT embryos. The results revealed that compared with the IVF embryos, the expression level of KDM4D in SCNT embryos was significantly lower at 8- and 16-cell stage, while the level of H3K9me3 in SCNT embryos was significantly higher at 2-cell, 8-cell, and blastocyst stage. Microinjection of KDM4D mRNA could promote the developmental ability of buffalo SCNT embryos. Furthermore, the expression level of ZGA-related genes such as ZSCAN5B, SNAI1, eIF-3a, and TRC at the 8-cell stage was significantly increased. Meanwhile, the pluripotency-related genes like POU5F1, SOX2, and NANOG were also significantly promoted at the blastocyst stage. The results were reversed after KDM4D was inhibited. Altogether, these results revealed that KDM4D could correct the H3K9me3 level, increase the expression level of ZGA and pluripotency-related genes, and finally, promote the developmental competence of buffalo SCNT embryos.