The objective of the present study was to analyze the level of intramuscular fat (IMF) in loin (musculus longissimus dorsi) and ham (musculus semimembranosus) and the level of subcutaneous fat in these cuts depending on breed, age and the expression level of FABP3 and LEPR genes. The results obtained showed that only the breed influenced on the level of both intramuscular and subcutaneous fat to the same extent (P ≤ 0.001). The age of animals had an effect on fat content of the cuts (P ≤ 0.001) and to a lower extent on the level of IMF in both muscles (P ≤ 0.05). We confirmed highly significant effect of breed and age on the LEPR mRNA abundance—the expression of the this gene increased significantly (P ≤ 0.01) with age and the highest expression was found for the Puławska breed in m. longissimus dorsi and for the Polish Landrace breed in m. semimembranosus. We observed the high correlations between the transcript level of the LEPR gene and the fat content of individual cuts (P ≤ 0.01). The expression level of FABP3 gene influenced the level of IMF (P ≤ 0.01), but not the level of subcutaneous fat in loin and ham.
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.
ObjectiveThe 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.MethodsRNA-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 Puławska breed) in order to evaluate the relationship of selected SNPs and histological characteristics, meat quality and carcasses traits.ResultsMapping 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.ConclusionThis 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.
The objective of this study was to analyse differences in individual fibre types in the histological profile of the longissimus dorsi muscle and their effect on pork carcass lean content and level of intramuscular fat (IMF) content, which determines palatability of meat and meat products. Analysis showed that the amount of type IIB fibres had a statistically significant (P<0.05) effect on the imf content of the longissimus dorsi muscle. Animals with more than 70% of type IIB fibres in this muscle were also characterized by larger loin eye area (P<0.01) and loin eye height (P<0.05). Analogous relationships were noted when the analysed group of animals was divided according to the diameter of type IIA fibres. IMF was negatively correlated to the percentage of type IIB fibres (r p = -0.162). Relationships with the other two fibre types were positive (IIA -r p = 0.097; I -r p = 0.187). It was found that increased percentage of type IIB fibres resulted in a slightly greater loin weight (r p = 0.176), higher loin eye height (r p = 0.136), larger loin eye area (r p = 0.265) and higher carcass lean content (r p = 0.204). Likewise, the increase in the number of type IIA and type I fibres decreased these parameters. Key words: pigs, histological profile, intramuscular fatThe skeletal muscles of humans and vertebrates are formed from different types of muscle fibres. These fibres can be classified according to their biochemical, functional and metabolic properties, among others. One of the classifications refers to myosin ATPase studies and distinguishes three major types of fibres: I, IIA and IIB. Phenotypic diversity of these fibres is determined by the presence of various myosin *The study was supported by the National Science Centre (grant no. N R12 0059 10). Unauthenticated 956heavy chain isoforms, which determines myosin ATPase activity and contractility (Majerczak et al., 2001).The observed profile of individual fibres in skeletal muscles, and thus the expression of different myosin isoforms is stable and genetically determined (Simoneau and Bouchard, 1995). Nevertheless, under certain conditions, e.g. the effect of hormonal factors, physical effort or electrical stimuli it may respond at the mRNA level, leading to degradation of existing proteins and formation of new microfilaments. However, these changes occur in a longer time period and largely depend on the duration of the stimulus (Majerczak et al., 2001; Spangenburg and Booth, 2003). This is why muscle fibre profile can be assumed to be stable when animals are kept under constant environmental conditions and are not exposed to stress and physical effort. Given such an assumption, considerable species, breed but also individual variation is observed in the amount and diameter of individual fibre types. Fibre types and their proportions in muscle determine muscle motility and its predisposition to physical effort. On the other hand, they may indirectly affect other physicochemical properties of muscle tissue. From the consumer's perspective, the propor...
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