Phenotypic features of dystrophin gene knockout pigs harboring a human artificial chromosome containing the entire dystrophin gene

Mammalian artificial chromosomes have enabled the introduction of extremely large amounts of genetic information into animal cells in an autonomously replicating, nonintegrating format. However, the evaluation of human artificial chromosomes (HACs) as novel tools for curing intractable hereditary disorders has been hindered by the limited efficacy of the delivery system. We generated dystrophin gene knockout (DMD-KO) pigs harboring the HAC bearing the entire human DMD via a somatic cell cloning procedure (DYS-HAC-cloned pig). Restored human dystrophin expression was confirmed by immunofluorescence staining in the skeletal muscle of the DYS-HAC-cloned pigs. Viability at the first month postpartum of the DYS-HAC-cloned pigs, including motor function in the hind leg and serum creatinine kinase level, was improved significantly when compared with that in the original DMD-KO pigs. However, decrease in systemic retention of the DYS-HAC vector and limited production of the DMD protein might have caused severe respiratory impairment with general prostration by 3 months postpartum. The results demonstrate that the use of transchromosomic cloned pigs permitted a straightforward estimation of the efficacy of the DYS-HAC carried in affected tissues/organs in a large-animal disease model, providing novel insights into the therapeutic application of exogenous mammalian artificial chromosomes.

Application of Enzyme-Linked Fluorescence Assay (ELFA) to Obtain In Vivo Matured Dog Oocytes through the Assessment of Progesterone Level

Successful dog cloning requires a sufficient number of in vivo matured oocytes as recipient oocytes for reconstructing embryos. The accurate prediction of the ovulation day in estrus bitches is critical for collecting mature oocytes. Traditionally, a specific serum progesterone (P4) range in the radioimmunoassay (RIA) system has been used for the prediction of ovulation. In this study, we investigated the use of an enzyme-linked fluorescence assay (ELFA) system for the measurement of P4. Serum samples of estrus bitches were analyzed using both RIA and ELFA, and the measured P4 values of ELFA were sorted into 11 groups based on the standard concentration measured in RIA and compared. In addition, to examine the tendency of changes in the P4 values in each system, the P4 values on ovulation day (from D - 6 to D + 1) in both systems were compared. The ELFA range of 5.0-12.0 ng/mL was derived from the RIA standard range of 4.0-8.0 ng/mL. The rates of acquired matured oocytes in RIA and ELFA were 55.47% and 65.19%, respectively. The ELFA system successfully produced cloned puppies after the transfer of the reconstructed cloned oocytes. Our findings suggest that the ELFA system is suitable for obtaining in vivo matured oocytes for dog cloning.

Generating Cloned Goats by Somatic Cell Nuclear Transfer-Molecular Determinants and Application to Transgenics and Biomedicine

The domestic goat (Capra aegagrus hircus), a mammalian species with high genetic merit for production of milk and meat, can be a tremendously valuable tool for transgenic research. This research is focused on the production and multiplication of genetically engineered or genome-edited cloned specimens by applying somatic cell nuclear transfer (SCNT), which is a dynamically developing assisted reproductive technology (ART). The efficiency of generating the SCNT-derived embryos, conceptuses, and progeny in goats was found to be determined by a variety of factors controlling the biological, molecular, and epigenetic events. On the one hand, the pivotal objective of our paper was to demonstrate the progress and the state-of-the-art achievements related to the innovative and highly efficient solutions used for the creation of transgenic cloned does and bucks. On the other hand, this review seeks to highlight not only current goals and obstacles but also future challenges to be faced by the approaches applied to propagate genetically modified SCNT-derived goats for the purposes of pharmacology, biomedicine, nutritional biotechnology, the agri-food industry, and modern livestock breeding.

CRISPR/Cas9-mediated MSTN disruption accelerates the growth of Chinese Bama pigs

CRISPR/Cas9-mediated genome editing technology is a simple and highly efficient and specific genome modification approach with wide applications in the animal industry. CRISPR/Cas9-mediated genome editing combined with somatic cell nuclear transfer rapidly constructs gene-edited somatic cell-cloned pigs for the genetic improvement of traits or simulation of human diseases. Chinese Bama pigs are an excellent indigenous minipig breed from Bama County of China. Research on genome editing of Chinese Bama pigs is of great significance in protecting its genetic resource, improving genetic traits and in creating disease models. This study aimed to address the disadvantages of slow growth and low percentage of lean meat in Chinese Bama pigs and to knock out the myostatin gene (MSTN) by genome editing to promote growth and increase lean meat production. We first used CRISPR/Cas9-mediated genome editing to conduct biallelic knockout of the MSTN, followed by somatic cell nuclear transfer to successfully generate MSTN biallelic knockout Chinese Bama pigs, which was confirmed to have significantly faster growth rate and showed myofibre hyperplasia when they reached sexual maturity. This study lays the foundation for the rapid improvement of production traits of Chinese Bama pigs and the generation of gene-edited disease models in this breed.

CRISPR/Cas9-Mediated Biallelic Knockout of IRX3 Reduces the Production and Survival of Somatic Cell-Cloned Bama Minipigs

Bama minipigs are a local pig breed that is unique to China and has a high development and utilization value. However, its high fat content, low feed utilization rate, and slow growth rate have limited its popularity and utilization. Compared with the long breeding cycle and high cost of traditional genetic breeding of pigs, clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) endonuclease 9 system (CRISPR/Cas9)-mediated gene editing can cost-effectively implement targeted mutations in animal genomes, thereby providing a powerful tool for rapid improvement of the economic traits of Bama minipigs. The iroquois homeobox 3 (IRX3) gene has been implicated in human obesity. Mouse experiments have shown that knocking out IRX3 significantly enhances basal metabolism, reduces fat content, and controls body mass and composition. This study aimed to knock out IRX3 using the CRISPR/Cas9 gene editing method to breed Bama minipigs with significantly reduced fat content. First, the CRISPR/Cas9 gene editing method was used to efficiently obtain IRX3-/- cells. Then, the gene-edited cells were used as donor cells to produce surviving IRX3-/- Bama minipigs using somatic cell cloning. The results show that the use of IRX3-/- cells as donor cells for the production of somatic cell-cloned pigs results in a significant decrease in the average live litter size and a significant increase in the average number of stillbirths. Moreover, the birth weight of surviving IRX3-/- somatic cell-cloned pigs is significantly lower, and viability is poor such that all piglets die shortly after birth. Therefore, the preliminary results of this study suggest that IRX3 may have important biological functions in pigs, and IRX3 should not be used as a gene editing target to reduce fat content in Bama minipigs. Moreover, this study shows that knocking out IRX3 does not favor the survival of pigs, and whether targeted regulation of IRX3 in the treatment of human obesity will also induce severe adverse consequences requires further investigation.

Generation of transgenic-cloned Huanjiang Xiang pigs systemically expressing enhanced green fluorescent protein

Huanjiang Xiang pig is a unique native minipig breed originating in Guangxi, China, and has great utility value in agriculture and biomedicine. Reproductive biotechnologies such as somatic cell nuclear transfer (SCNT) and SCNT-mediated genetic modification show great potential value in genetic preservation and utilization of Huanjiang Xiang pigs. Our previous work has successfully produced cloned and transgenic-cloned embryos using somatic cells from a Huanjiang Xiang pig. In this study, we firstly report the generation of transgenic-cloned Huanjiang Xiang pigs carrying an enhanced green fluorescent protein (eGFP) gene. A total of 504 SCNT-derived embryos were transferred to two surrogate recipients, one of which became pregnant and gave birth to three live piglets. Exogenous eGFP transgene had integrated in all of the three Huanjiang Xiang piglets identified by genotyping. Furthermore, expression of eGFP was also detected from in vitro cultured skin fibroblast cells and various organs or tissues from positive transgenic-cloned Huanjiang Xiang pigs. The present work provides a practical method to preserve this unique genetic resource and also lays a foundation for genetic modification of Huanjiang Xiang pigs with improved values in agriculture and biomedicine.

Modeling lethal X-linked genetic disorders in pigs with ensured fertility

The development of therapies for rare and intractable genetic disorders represents a significant unmet medical need. Disease model pigs characterized by physiological, anatomical, and pathogenetic similarities to humans allow translational studies to be performed, yielding valuable data that can be extrapolated to patients. The establishment of an efficient reproduction system is a key element in the practical application of disease model pigs, which often suffer from reproductive inability due to severe symptoms. Here, we showed that the valuable trait of genetically modified disease model pigs can be maximized by generating unique chimeric boars composed of mutant and normal cells.

Genetically engineered pigs play an indispensable role in the study of rare monogenic diseases. Pigs harboring a gene responsible for a specific disease can be efficiently generated via somatic cell cloning. The generation of somatic cell-cloned pigs from male cells with mutation(s) in an X chromosomal gene is a reliable and straightforward method for reproducing X-linked genetic diseases (XLGDs) in pigs. However, the severe symptoms of XLGDs are often accompanied by impaired growth and reproductive disorders, which hinder the reproduction of these valuable model animals. Here, we generated unique chimeric boars composed of mutant cells harboring a lethal XLGD and normal cells. The chimeric boars exhibited the cured phenotype with fertility while carrying and transmitting the genotype of the XLGD. This unique reproduction system permits routine production of XLGD model pigs through the male-based breeding, thereby opening an avenue for translational research using disease model pigs.