cDNA Cloning of Goat DNA Methyltransferase 1, Screening of shRNA Vectors and Influences to Development of Nuclear Transfer Embryos

Sheep and Goat Genome Engineering: From Random Transgenesis to the CRISPR Era

Sheep and goats are valuable livestock species that have been raised for their production of meat, milk, fiber, and other by-products. Due to their suitable size, short gestation period, and abundant secretion of milk, sheep and goats have become important model animals in agricultural, pharmaceutical, and biomedical research. Genome engineering has been widely applied to sheep and goat research. Pronuclear injection and somatic cell nuclear transfer represent the two primary procedures for the generation of genetically modified sheep and goats. Further assisted tools have emerged to enhance the efficiency of genetic modification and to simplify the generation of genetically modified founders. These tools include sperm-mediated gene transfer, viral vectors, RNA interference, recombinases, transposons, and endonucleases. Of these tools, the four classes of site-specific endonucleases (meganucleases, ZFNs, TALENs, and CRISPRs) have attracted wide attention due to their DNA double-strand break-inducing role, which enable desired DNA modifications based on the stimulation of native cellular DNA repair mechanisms. Currently, CRISPR systems dominate the field of genome editing. Gene-edited sheep and goats, generated using these tools, provide valuable models for investigations on gene functions, improving animal breeding, producing pharmaceuticals in milk, improving animal disease resistance, recapitulating human diseases, and providing hosts for the growth of human organs. In addition, more promising derivative tools of CRISPR systems have emerged such as base editors which enable the induction of single-base alterations without any requirements for homology-directed repair or DNA donor. These precise editors are helpful for revealing desirable phenotypes and correcting genetic diseases controlled by single bases. This review highlights the advances of genome engineering in sheep and goats over the past four decades with particular emphasis on the application of CRISPR/Cas9 systems.

Combination of S-adenosylhomocysteine and scriptaid, a non-toxic epigenetic modifying reagent, modulates the reprogramming of bovine somatic-cell nuclear transfer embryos

The goal of this study was to improve the development of bovine somatic-cell nuclear transfer (SCNT) embryos by optimizing the combination of DNA methyltransferases inhibitor S-adenosylhomocysteine (SAH) and histone deacetylase inhibitor Scriptaid (SPD). A. 4 × 4-factor design of different drug combinations (0, 0.75, 1.0, and 1.5 mM SAH and 0, 5, 250, and 500 nM SPD) was used to identify an optimal combination of 0.75 mM SAH and 250 nM SPD that improved the developmental competence of bovine SCNT embryos. Further experiments using this combination revealed that methylation levels of CpG islands near exon 1 of the pluripotent gene SOX2; the epigenetic-related gene HDAC3 and DNMT3a; imprinted genes XIST and PEG3; as well as apoptosis-related genes BCL2 and BAX were returned to levels similar to those of in vitro fertilized (IVF) embryo after treatment, which also normalized transcript levels for these genes. This combination also returned global DNA methylation to a normal level, correcting H4K12ac levels while enhancing H3K9ac levels. Thus, the combined application of 0.75 mM SAH and 250 nM SPD can significantly improve the reprogramming of bovine SCNT embryos by stabilizing how embryos utilize their genomes.