Follistatin (FST) is an important regulator of skeletal muscle growth and adipose deposition through its ability to bind to several members of the transforming growth factor-β (TGF-β) superfamily, and thus may be a good candidate for future animal breeding programs.  However, the molecular mechanisms underlying the phenotypic changes have yet to be clarified in pig.  We generated transgenic (TG) pigs that express human FST specifically in skeletal muscle tissues and characterized the phenotypic changes compared with the same tissues in wild-type pigs.  The TG pigs showed increased skeletal muscle growth, decreased adipose deposition, and improved metabolism status (P<0.05).  Transcriptome analysis detected important roles of the PIK3–AKT signaling pathway, calcium-mediated signaling pathway, and amino acid metabolism pathway in FST-induced skeletal muscle hypertrophy, and depot-specific oxidative metabolism changes in psoas major muscle.  Furthermore, the lipid metabolism-related process was changed in adipose tissue in the TG pigs.  Gene set enrichment analysis revealed that genes related to lipid synthesis, lipid catabolism, and lipid storage were down-regulated (P<0.01) in the TG pigs for subcutaneous fat, whereas genes related to lipid catabolism were significantly up-regulated (P<0.05) in the TG pigs for retroperitoneal fat compared with their expression levels in wild-type pigs.  In liver, genes related to the TGF-β signaling pathway were over-represented in the TG pigs, which is consistent with the inhibitory role of FST in regulating TGF-β signaling.  Together, these results provide new insights into the molecular mechanisms underlying the phenotypic changes in pig.

    The transcription activator-like effector nuclease (TALEN) technique combined with the somatic cell nuclear transfer (SCNT) method has been successfully applied for creating genetically modified pigs. However, methods for isolating cells with biallelic indels requires further improvement because of the relatively low enrichment efficiency of mutated somatic cells. Moreover, little is known regarding the off-target effects of the TALEN system and the heredity of TALEN-modified pigs. In this study, an efficient method to increase the enrichment efficiency of TALEN-mediated biallelic knockout (KO) cells was established, and corresponding genetically modified pigs with the expected genotype were generated whose off-target effect, fertility and heredity characteristics were aslo evaluated. Two TALEN pairs were constructed to target the porcine α-1,3-galactosyltransferase (GGTA1) gene locus. TALEN mRNA was transfected into the ear ?broblasts followed by the enrichment of α-Gal null cells of minipigs using isolectin B4 (IB4) lectin and magnetic beads. A total of 115 cell colonies were formed and validated to be GGTA1 KO cells by sequencing and 10 biallelic KO cell colonies were used as nuclear donors for SCNT. Thirty GGTA1 biallelic KO piglets were successfully delivered and grew normally. Seventeen potential off-target sites were investigated, and no off-target events were detected in the live piglets. To determine the fertility and heredity characteristics of TALEN-modified pigs, 10 mature founders were mated with each other and the mutations were determined to be transmitted to the F1 piglets. We established a robust and safe technology for developing genetically modified pig lines with expected genotypes for agricultural breeding and biomedical application.