Temporal Expression Patterns of Twelve Genes during Fetal and Postnatal Skeletal Muscle Development in Pigs

Characterizing the temporal expression patterns of genes throughout fetal myogenesis and postnatal skeletal muscle hypertrophy in pigs is critical to obtain a better understanding of the genes involved in these important processes. Previous transcriptome-wide expression profiling studies utilizing the 70-mer Pigoligoarray microarray revealed many genes exhibiting dynamic expression during fetal and postnatal development. The objective of this study was to confirm expression profiles for 12 genes in pig Longissimus dorsi (LD) skeletal muscle at seven developmental stages: 57, 70, and 105 days of gestation (dg), birth, and 1, 3, and 5 weeks postnatal. Total RNA was extracted from LD samples of male and female fetuses (n≈3 per sex per stage) obtained from Yorkshire x Landrace gilts. Expression profiles for each gene at each stage were determined using real-time RT-qPCR assays with TaqMan chemistry. Target genes were ATF4, ATXN10, BTC, CACYBP, CYTH2, DCN, DLK1, FST, MYOZ1, NRAP, USP13, and WRAP73, along with PPIA, HPRT1, and RPS18 for normalization. The relative expression of each gene (∆Cts) was used as the response variable in a linear model including fixed effects of sex, age, and sex by age interaction. Results of this linear model were analyzed with ANOVA to assess the significance of each effect. Tukey-Kramer adjustments were used to conduct pairwise comparisons between developmental stages for each gene. A significant effect of age was observed on the expression of all target genes except for ATXN10 (p-value range: 5.89e-14 to 0.007). Six genes (ATF4, BTC, CACYBP, MYOZ1, NRAP, and USP13) increased in expression from 57 dg to 5 wk postnatal, while DLK1 decreased over time. Four genes (CYTH2, DCN, FST, and WRAP73) exhibited variable expression throughout development. These expression patterns were consistent with previously observed patterns of expression obtained from microarray experiments. These genes have been shown in other species to be involved in multiple biological processes including: metabolic disease, lipid metabolism, and molecular transport (CACYBP, DLK1, USP13, and WRAP73); organ morphology, skeletal and muscular system development and function, and skeletal and muscular disorders (BTC, DCN, MYOZ1, and NRAP); and cell signaling, DNA replication, recombination and repair, and nucleic acid metabolism (CYTH2 and FST). Further research into temporal gene expression patterns will enhance our understanding of the regulation of muscle development in pigs.