[Effects of RNA interference on the porcine NHEJ pathway repair factors on HR efficiency].

Non-homologous end-joining (NHEJ) is the predominant DNA double-strand break (DSB) repair pathway in mammalian cells. It inhibits the efficiency of homologous recombination (HR) by competing for DSB targets. To improve the efficiency of HR in porcine fetal fibroblasts (PFFs), several RNA interference (RNAi) systems were designed to knockdown NHEJ key molecules, such as polynucleotide kinase/phosphatase (PNKP), DNA ligase IV (LIG4) and NHEJ1. The results show that siRNA significantly knocked down LIG4, PNKP and NHEJ1 expression. Suppression of PNKP dramatically increased the efficiency of single-strand annealing (SSA), double-strand DNA (dsDNA) and single-strand DNA (ssODN) mediated homology-directed repair (HDR) by 55.7%, 37.4% and 73.1% after transfected with the SSA-GFP reporter, HDR-GFP system or ssODN-GFP system, respectively; whereas knockdown of LIG4 and NHEJ1 repair factors significantly increased dsDNA or ssODN-mediated HDR efficiency by 37.5% and 76.9%, respectively.

Effects of parameters, plasmid dosages and topological structures on transfection efficiency of porcine fetal fibroblasts using different electroporators.

To obtain an ideal transfection efficiency of porcine fetal fibroblasts, fluorescence activated cell sorting (FACS) was used to optimize parameters for transfection of porcine fetal fibroblasts (PFFs) with ECM? 830, NEPA 21 and Nucleofector? 2b in different conditions such as electroporation parameters, plasmid dosages and topological structures. The results show that the optimum poring pulse parameter of NEPA 21 is voltage 200 V, continuous 3 ms, interval 50 ms, 3 times, voltage attenuation range of 10%; and the transfection efficiency of Nucleofector? 2b is highest under U-023 program. Under the optimum conditions, FACS analysis demonstrates that Nucleofector? 2b and ECM? 830 have the highest transfection efficiency when transfecting 10 µg supercoiled plasmids into PFFs, and 8 µg for NEPA 21. Supercoiled plasmids show higher transfection efficiencies than linearized plasmids. Moreover, Nucleofector? 2b has the highest transfection efficiency among the three electroporation instruments. This study paves the way to generate transgenic or gene editing pigs with high efficiency.

Advances in site-specific integration of transgene in animal genome.

The traditional transgenic technologies, such as embryo microinjection, transposon-mediated integration, or lentiviral transfection, usually result in random insertions of the foreign DNA into the host genome, which could have various disadvantages in the establishment of transgenic animals. Therefore, a strategy for site-specific integration of a transgene is needed to generate genetically modified animals with accurate and identical genotypes. However, the efficiency for site-specific integration of transgene is very low, which is mainly caused by two issues. The first one is the low efficiency of inducing double-strand break (DSB) at the target site of host genome in the initial process. The second one is the low efficiency of homologous recombination repair (HDR) between the target site and the donor plasmid carrying homologous arm and foreign genes. HDR is the most common mechanism for site-specific integration of a transgene. DSBs can stimulate DNA repair mainly by two competitive mechanisms, HDR and nonhomologous end joining (NHEJ). Hence, activation of HDR or inhibition of NHEJ can promote the HDR in the integration processes, thereby optimizing a specific targeting of the transgene. In this review, we summarize the recent advances in strategies for improving the site-specific integration of foreign transgene in transgenic technologies.

Establishment of porcine Xist knockout model using CRISPR/Cas9 system.

Somatic cell nuclear transfer technique has great applications in livestock breeding, production of genetically modified animals, rescue of endangered species and treatment of human diseases. However, the currently low efficiency in animals cloning, an average of less than 5%, greatly hindered the rapid development of this technique. Among many factors which affect the efficiency of cloning pigs, X chromosome inactivation is an important one. Moreover, Xist gene is closely related to X chromosome inactivation, suggesting that it may directly or indirectly affects cloning efficiency. In this study, multiple sgRNAs were designed based on the CRISPR/Cas system, and two sites (Target 3 and Target 4) whose mutation efficiency were 1% and 3% at the cellular level were selected. We successfully knocked out Xist with 100% efficiency by microinjecting sgRNAs for Target 3 and Target 4 in embryo. Finally, 6 cloning piglets were born including two Xist-fully-knockout piglets. The follow-up studies on increasing cloning efficiency can be carried out based on the Xist-knockout model.