Production of a Cloned Offspring and CRISPR/Cas9 Genome Editing of Embryonic Fibroblasts in Cattle

Somatic Cell Nuclear Transfer (SCNT) technique was used to produce the first viable cloned cattle offspring in Russia. Whole-genome SNP genotyping confirmed that the cloned calf was identical to the fibroblast cell line that was used for SCNT. CRISPR/Cas9 approach was subsequently used to knock out genes for beta-lactoglobulin gene (PAEP) and the beta-lactoglobulin-like protein gene (LOC100848610) in the fibroblast cells. Gene editing (GE) efficiency was 4.4% for each of these genes. We successfully obtained single-cell-derived fibroblast colonies containing PAEP and LOC100848610 knockouts, which will be used to produce beta-lactoglobulin-deficient cattle.

Testes of DAZL null neonatal sheep lack prospermatogonia but maintain normal somatic cell morphology and marker expression

Multiplying the germline would increase the number of offspring that can be produced from selected animals, accelerating genetic improvement for livestock breeding. This could be achieved by producing multiple chimaeric animals, each carrying a mix of donor and host germ cells in their gonads. However, such chimaeric germlines would produce offspring from both donor and host genotypes, limiting the rate of genetic improvement. To resolve this problem, we disrupted the RNA-binding protein DAZL and generated germ cell-deficient host animals. Using Cas9-mediated homology-directed repair (HDR), we introduced a DAZL loss-of-function mutation in male ovine fetal fibroblasts. Following manual single cell isolation, 4/48 (8.3%) of donor cell strains were homozygously HDR-edited. Sequence-validated strains were used as nuclear donors for somatic cell cloning to generate three lambs, which died at birth. All DAZL null male neonatal sheep lacked germ cells on histological sections and showed greatly reduced germ cell markers. Somatic cells within their testes were morphologically intact and expressed normal levels of lineage-specific markers, suggesting that the germ cell niche remained intact. This extends the DAZL mutant phenotype beyond mice into agriculturally relevant ruminants, providing a pathway for using absolute germline transmitters in rapid livestock improvement.

Whole-Genome Methylation Analysis Reveals Epigenetic Variation in Cloned and Donor Pigs

Somatic cloning has had a significant impact on the life sciences and is important in a variety of processes, including medical research and animal production. However, the application of somatic cloning has been limited due to its low success rate. Therefore, potential epigenetic variations between cloned and donor animals are still unclear. DNA methylation, one of the factors which is responsible for phenotypic differences in animals, is a commonly researched topic in epigenetic studies of mammals. To investigate the epigenetic variations between cloned and donor animals, we selected blood and ear fibroblasts of a donor pig and a cloned pig to perform whole-genome bisulfite sequencing (WGBS). A total of 215 and 707 differential methylation genes (DMGs) were identified in blood and ear fibroblasts, respectively. Functional annotation revealed that DMGs are enriched in many pathways, including T/B or natural killer (NK) cell differentiation, oocyte maturation, embryonic development, and reproductive hormone secretion. Moreover, 22 DMGs in the blood and 75 in the ear were associated with immune responses (e.g., CD244, CDK6, CD5, CD2, CD83, and CDC7). We also found that 18 DMGs in blood and 53 in ear fibroblasts were involved in reproduction. Understanding the expression patterns of DMGs, especially in relation to immune responses and reproduction, will reveal insights that will aid the advancement of future somatic cloning techniques in swine.