Hepatic Transcriptome Analysis Reveals Genes, Polymorphisms, and Molecules Related to Lamb Tenderness.

Tenderness is a key meat quality trait that determines the public acceptance of lamb consumption, so genetic improvement toward lamb with higher tenderness is pivotal for a sustainable sheep industry. However, unravelling the genomics controlling the tenderness is the first step. Therefore, this study aimed to identify the transcriptome signatures and polymorphisms related to divergent lamb tenderness using RNA deep sequencing. Since the molecules and enzymes that control muscle growth and tenderness are metabolized and synthesized in the liver, hepatic tissues of ten sheep with divergent phenotypes: five high- and five low-lamb tenderness samples were applied for deep sequencing. Sequence analysis identified the number of reads ranged from 21.37 to 25.37 million bases with a mean value of 22.90 million bases. In total, 328 genes are detected as differentially expressed (DEGs) including 110 and 218 genes that were up- and down-regulated, respectively. Pathway analysis showed steroid hormone biosynthesis as the dominant pathway behind the lamb tenderness. Gene expression analysis identified the top high (such as TP53INP1, CYP2E1, HSD17B13, ADH1C, and LPIN1) and low (such as ANGPTL2, IGFBP7, FABP5, OLFML3, and THOC5) expressed candidate genes. Polymorphism and association analysis revealed that mutation in OLFML3, ANGPTL2, and THOC5 genes could be potential candidate markers for tenderness in sheep. The genes and pathways identified in this study cause variation in tenderness, thus could be potential genetic markers to improve meat quality in sheep. However, further validation is needed to confirm the effect of these markers in different sheep populations so that these could be used in a selection program for lamb with high tenderness.

Association study and expression analysis of olfactomedin like 3 gene related to meat quality, carcass characteristics, retail meat cut, and fatty acid composition in sheep.

OBJECTIVE: The objective of this study was to identify polymorphism in olfactomedin like 3 (OLFML3) gene, and association analysis with meat quality, carcass characteristics, retail meat cut, and fatty acid composition in sheep, and expression quantification of OLFML3 gene in phenotypically divergent sheep. METHODS: A total of 328 rams at the age of 10 to 12 months with an average body weight of 26.13 kg were used. A novel polymorphism was identified using high-throughput sequencing in sheep and genotyping of OLFML3 polymorphism was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Among 328 rams, 100 rams representing various sheep genotypes were used for association study and proc general linear model was used to analyse association between genotypes and phenotypic traits. Quantitative real-time polymerase chain reaction (qRT-PCR) was used for the expression analysis of OLFML3 mRNA in phenotypically divergent sheep population. RESULTS: The findings revealed a novel polymorphism in the OLFML3 gene (g.90317673 C>T). The OLFML3 gene revealed three genotypes: CC, CT, and TT. The single nucleotide polymorphism (SNP) was found to be significantly (p<0.05) associated with meat quality traits such as tenderness and cooking loss; carcass characteristics such as carcass length; retail meat cut such as pelvic fat in leg, intramuscular fat in loin and tenderloin, muscle in flank and shank; fatty acids composition such as tridecanoic acid (C13:0), palmitoleic acid (C16:1), heptadecanoic acid (C17:0), ginkgolic acid (C17:1), linolenic acid (C18:3n3), arachidic acid (C20:0), eicosenoic acid (C20:1), arachidonic acid (C20:4n6), heneicosylic acid (C21:0), and nervonic acid (C24:1). The TT genotype was associated with higher level of meat quality, carcass characteristics, retail meat cut, and some fatty acids composition. However, the mRNA expression analysis was not different among genotypes. CONCLUSION: The OLFML3 gene could be a potential putative candidate for selecting higher quality sheep meat, carcass characteristics, retail meat cuts, and fatty acid composition in sheep.

Hepatic transcriptome analysis identifies genes, polymorphisms and pathways involved in the fatty acids metabolism in sheep.

Fatty acids (FA) in ruminants, especially unsaturated FA (USFA) have important impact in meat quality, nutritional value, and flavour quality of meat, and on consumer's health. Identification of the genetic factors controlling the FA composition and metabolism is pivotal to select sheep that produce higher USFA and lower saturated (SFA) for the benefit of sheep industry and consumers. Therefore, this study was aimed to investigate the transcriptome profiling in the liver tissues collected from sheep with divergent USFA content in longissimus muscle using RNA deep-sequencing. From sheep (n = 100) population, liver tissues with higher (n = 3) and lower (n = 3) USFA content were analysed using Illumina HiSeq 2500. The total number of reads produced for each liver sample were ranged from 21.28 to 28.51 million with a median of 23.90 million. Approximately, 198 genes were differentially regulated with significance level of p-adjusted value <0.05. Among them, 100 genes were up-regulated, and 98 were down-regulated (p<0.01, FC>1.5) in the higher USFA group. A large proportion of key genes involved in FA biosynthesis, adipogenesis, fat deposition, and lipid metabolism were identified, such as APOA5, SLC25A30, GFPT1, LEPR, TGFBR2, FABP7, GSTCD, and CYP17A. Pathway analysis revealed that glycosaminoglycan biosynthesis- keratan sulfate, adipokine signaling, galactose metabolism, endocrine and other factors-regulating calcium metabolism, mineral metabolism, and PPAR signaling pathway were playing important regulatory roles in FA metabolism. Importantly, polymorphism and association analyses showed that mutation in APOA5, CFHR5, TGFBR2 and LEPR genes could be potential markers for the FA composition in sheep. These polymorphisms and transcriptome networks controlling the FA variation could be used as genetic markers for FA composition-related traits improvement. However, functional validation is required to confirm the effect of these SNPs in other sheep population in order to incorporate them in the sheep breeding program.

Transcriptome signature of liver tissue with divergent mutton odour and flavour using RNA deep sequencing.

Mutton consumption is less popular in many Asian countries including Indonesia, whose consumers often complain about the unpleasant flavour and odour of the meat. The main causes of mutton odour are the two compounds of branched chain fatty acid (BCFA): methylnonanoic (MNA), phenol, 3-methyl (MP), 4-methylnonanoic (MNA) and 4-ethyloctanoic (EOA) present in all the adipose tissue; and the 3-methylindole (MI) or skatole and indole, which are originated from pastoral diets. It is crucial to understand the genetic mechanism of mutton odour and flavour (MOF) to select sheep for lower BCFA and indole thus reduce the unpleasant flavour of meat. The aim of the present study was to investigate transcriptome profiling in liver tissue with divergent MOF using RNA deep sequencing. Liver tissues from higher (n = 3) and lower (n = 3) MOF sheep were analysed using Illumina HiSeq 2500. The total number of reads produced for each liver sample ranged from 21.37 to 25.37 million. Approximately 103 genes were differentially expressed (DEGs) with significance level of p-adjusted value <0.05. Among them, 60 genes were up-regulated, and 43 were down-regulated (p < 0.01, FC > 1.5) in higher MOF group. Differentially regulated genes in high MOF liver samples were enriched in biological processes such as cellular response to chemical stimulus and endogenous stimulus; cellular components such as such as basement membrane and extracellular matrix; and molecular functions such as haeme binding and oxidoreductase activity. Among the DEGs, metabolic phase I related genes belonging to the cytochrome P450 CYP2A6 were dominantly expressed. Additionally, phase II conjugation genes including UDP glucuronosyltransferases UGT2B18, sulfotransferase SULT1C1, and glutathione S-transferase GSTM1 were identified. The dominant candidate genes for SOF could be cytochrome P450, sodium-channel protein, transmembrane protein, glutathione transferase, UDP glucuronosyltransferases and sulfotransferase. Pathway analysis identified steroid hormone biosynthesis and chemical carcinogenesis by cytochrome P450 pathways which may play important roles in MOF-related molecules metabolism. This work highlighted potential genes and gene-networks that may affect meat off flavour and odour in sheep.