Progress on abnormal development of cloned pigs generated by somatic cell transfer nuclear

Cloning, also known as somatic cell nuclear transfer (SCNT), is an asexual reproduction technique that reprograms differentiated cells to the totipotent state, and generates offspring with a genotype identical to the donor cells. Pig cloning technique holds great promise for propagating excellent breeding boars, generating genetically modified pigs, protecting rare and endangered pigs and studying the mechanisms of somatic cell nucleus reprogramming. However, cloned pigs suffer from various developmental defects, including low birth rate, low birth weight, and high stillbirth occurrence, neonatal mortality and congenital malformations, which severely hamper their applications. Errors in epigenetic reprogramming of donor nucleus are considered as the main causes of low cloning efficiency and abnormal embryonic development in cloned embryos and animals. However, most studies to correct the errors in epigenetic reprogramming of cloned pig embryos have not substantially improved the birth and survival rates of cloned pigs. In this review, we summarize the abnormal phenotypes, causes of abnormal development of cloned pigs and effective methods for improving pig cloning efficiency, thereby providing a reference for the future research to improve the development and survival rates of cloned pig embryos and cloned pigs.