Examining the Genetic Background of Porcine Muscle Growth and Development Based on Transcriptome and miRNAome Data.

Recently, selection in pigs has been focused on improving the lean meat content in carcasses; this focus has been most evident in breeds constituting a paternal component in breeding. Such sire-breeds are used to improve the meat quantity of cross-breed pig lines. However, even in one breed, a significant variation in the meatiness level can be observed. In the present study, the comprehensive analysis of genes and microRNA expression profiles in porcine muscle tissue was applied to identify the genetic background of meat content. The comparison was performed between whole gene expression and miRNA profiles of muscle tissue collected from two sire-line pig breeds (Pietrain, Hampshire). The RNA-seq approach allowed the identification of 627 and 416 differentially expressed genes (DEGs) between pig groups differing in terms of loin weight between Pietrain and Hampshire breeds, respectively. The comparison of miRNA profiles showed differential expression of 57 microRNAs for Hampshire and 34 miRNAs for Pietrain pigs. Next, 43 genes and 18 miRNAs were selected as differentially expressed in both breeds and potentially related to muscle development. According to Gene Ontology analysis, identified DEGs and microRNAs were involved in the regulation of the cell cycle, fatty acid biosynthesis and regulation of the actin cytoskeleton. The most deregulated pathways dependent on muscle mass were the Hippo signalling pathway connected with the TGF-ß signalling pathway and controlling organ size via the regulation of ubiquitin-mediated proteolysis, cell proliferation and apoptosis. The identified target genes were also involved in pathways such as the FoxO signalling pathway, signalling pathways regulating pluripotency of stem cells and the PI3K-Akt signalling pathway. The obtained results indicate molecular mechanisms controlling porcine muscle growth and development. Identified genes (SOX2, SIRT1, KLF4, PAX6 and genes belonging to the transforming growth factor beta superfamily) could be considered candidate genes for determining muscle mass in pigs.

Screening for candidate genes related with histological microstructure, meat quality and carcass characteristic in pig based on RNA-seq data.

OBJECTIVE: The aim of the present study was to identify genetic variants based on RNA-seq data, obtained via transcriptome sequencing of muscle tissue of pigs differing in muscle histological structure, and to verify the variants' effect on histological microstructure and production traits in a larger pig population. METHODS: RNA-seq data was used to identify the panel of single nucleotide polymorphisms (SNPs) significantly related with percentage and diameter of each fiber type (I, IIA, IIB). Detected polymorphisms were mapped to quantitative trait loci (QTLs) regions. Next, the association study was performed on 944 animals representing five breeds (Landrace, Large White, Pietrain, Duroc, and native Pulawska breed) in order to evaluate the relationship of selected SNPs and histological characteristics, meat quality and carcasses traits. RESULTS: Mapping of detected genetic variants to QTL regions showed that chromosome 14 was the most overrepresented with the identification of four QTLs related to percentage of fiber types I and IIA. The association study performed on a 293 longissimus muscle samples confirmed a significant positive effect of transforming acidic coiled-coil-containing protein 2 (TACC2) polymorphisms on fiber diameter, while SNP within forkhead box O1 (FOXO1) locus was associated with decrease of diameter of fiber types IIA and IIB. Moreover, subsequent general linear model analysis showed significant relationship of FOXO1, delta 4-desaturase, sphingolipid 1 (DEGS1), and troponin T2 (TNNT2) genes with loin 'eye' area, FOXO1 with loin weight, as well as FOXO1 and TACC2 with lean meat percentage. Furthermore, the intramuscular fat content was positively associated (p<0.01) with occurrence of polymorphisms within DEGS1, TNNT2 genes and negatively with occurrence of TACC2 polymorphism. CONCLUSION: This study's results indicate that the SNP calling analysis based on RNA-seq data can be used to search candidate genes and establish the genetic basis of phenotypic traits. The presented results can be used for future studies evaluating the use of selected SNPs as genetic markers related to muscle histological profile and production traits in pig breeding.

Transcriptomic gene profiling of porcine muscle tissue depending on histological properties.

In pig, the histological profile of muscle tissue, especially the proportion of individual fiber types, is one of the main factors affecting meat quality properties. In the present research, RNA sequencing (RNA-seq) by using next generation sequencing method was applied to estimate the whole gene expression profile of Longissimus lumborum muscle of pigs (Large White breed) differing in the percentage of two fiber types (slow-twitch (type I) fibers and fast-twitch glycolytic (type IIB) fibers). The RNA-seq approach allowed us to identify 355 differentially expressed genes (DEGs) indicated as significant (false discovery rate-adjusted P < 0.05) using three types of software: DESeq2, edgeR and baySeq. Detected genes and pathways deregulated in muscle depending on tissue microstructure were associated with: metabolic processes - 158 genes; cellular processes - 122; biological regulation - 62; localization - 51; and 35 genes with developmental processes. The DEGs were included in: PI3K-Akt; FoxO and MAPK signaling pathways, regulation of actin cytoskeleton, lysine degradation and insulin signaling pathway as well as mTOR and Hippo signaling pathways. These results highlight the mainly metabolic pathways related to glucose metabolism and contraction processes of muscle cells. Detection of genes involved in variation of fiber-type distribution will be useful in understanding of the genetic factors affecting muscle structure, metabolic process and indirectly, meat quality traits.