The length of guide RNA and target DNA heteroduplex effects on CRISPR/Cas9 mediated genome editing efficiency in porcine cells

The clustered regularly interspaced short palindrome repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system is a versatile genome editing tool with high efficiency. A guide sequence of 20 nucleotides (nt) is commonly used in application of CRISPR/Cas9; however, the relationship between the length of the guide sequence and the efficiency of CRISPR/Cas9 in porcine cells is still not clear. To illustrate this issue, guide RNAs of different lengths targeting the EGFP gene were designed. Specifically, guide RNAs of 17 nt or longer were sufficient to direct the Cas9 protein to cleave target DNA sequences, while 15 nt or shorter guide RNAs had loss-of-function. Full-length guide RNAs complemented with mismatches also showed loss-of-function. When the shortened guide RNA and target DNA heteroduplex (gRNA:DNA heteroduplex) was blocked by mismatch, the CRISPR/Cas9 would be interfered with. These results suggested the length of the gRNA:DNA heteroduplex was a key factor for maintaining high efficiency of the CRISPR/Cas9 system rather than weak bonding between shortened guide RNA and Cas9 in porcine cells.

Porcine VHL gene cloning and construction of VHL knockdown cloned embryos / 生物工程学报

Von Hippel-Lindau (VHL) disease is an autosomal dominant disorder and its clinical manifestation including haemangioblastomas of the central nervous system, renal cell carcinoma, haeochromocytomas, and pancreatic cyst. The deletion, mutation and promoter methylation of VHL gene can cause VHL disease. Swine is considered as an ideal model for human disease because of its physiological and anatomical similarity to human. We cloned pig VHL gene that is 2 725 bp in length. VHL highly expressed in adrenal gland, liver, pancreas, heart and testis. We designed 5 shRNAs and screened the most effective interference RNA fragment with a knockdown efficiency of 72%. Porcine embryonic fibroblasts stably transfected with pGenesil-shRNA vector were used as donor cells for nuclear transfer and there was no significant difference of embryo development compared with the control group. Moreover, VHL was efficiently knocked-down with efficiency of 71% in porcine cloned blastocyst, these results lay a solid foundation for constructing the VHL knock-down model of pig.

Cloning and gene expression of sall4b gene in pig / 生物工程学报

Sall4, a member of sall4 gene family, plays important roles in embryo development; organogenesis as well as pluripotency maintenance and re-establishment. There are two isoforms of Sall4, Sall4A and Sall4B. The sequence of porcine sall4 gene is still not reported. Because of its distinct role in maintaining the pluripotent state of stem cells, we cloned and sequenced porcine sall4 gene and assessed its expression in pig tissues and embryos. One 2 372 bp nucleotide sequence representing the full-length cDNA of pig sall4 was obtained by 5'and 3'RACE. Analyses of putative protein sequence showed a 70% to 80% identity with isoform Sall4B of human and mouse. Comparing with Sall4A, the identity reduced to 30% to 55% because of the loss of a zinc-finger domain-rich fragment. Assessment of sall4b expression in porcine tissues by Real-time PCR showed that it expressed most strongly in ovary and stronger in spleen, lung, heart and testis. For preimplantation embryos, the expression level was lower in 4-cell embryos compared with other stages. Immuno-fluorescence analysis of Sall4 on porcine preimplantation embryos indicated that it expressed in all the preimplantation embryos and located in nucleus, in blastocyst it preferentially limited in ICM cells. Expression pattern in early embryos suggest that pig sall4b is associated with pluripotency and might be a new and useful reprogramming factor for establishing pig induced pluripotent stem cell lines.