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Introduction: In Northeast China, Dorper and Australian White rams are commonly crossbred with small-tailed Han (STH) ewes to improve the offspring's meat yield and quality. However, the differences in traits and the flavor between the crossbred sheep and STH sheep remain unclear. In addition, the candidate genes potentially influencing the meat quality in the three sheep breeds require further verification. Methods: A total of 18 2-month-old healthy rams were raised over a period of 5 months, which included 6 STH, 6 Dorper and small-tailed Han crossbred (Do × STH), and 6 Australian white and small-tailed Han crossbred (Au × STH) offspring. The differences in slaughter, meat quality traits, fatty acid and amino acid composition in the muscular longissimus dorsi (MLD), and volatile compounds in the semitendinosus muscle were compared between the sheep breeds. The candidate genes related to intramuscular fat (IMF) content and fatty acids were validated. Results: The results of this study revealed that the crossbred sheep had higher body weight, carcass weight, bone weight, net meat weight, and IMF content than the STH sheep (p < 0.05). The Do × STH offspring had a higher pH value (24 h), moisture content, and cooking percentage; they also had redder and brighter meat color. The content of myristate, palmitic, and margaric acids in the crossbred sheep was higher than that in the STH sheep (p < 0.05). The Do × STH offspring had the highest saturated fatty acid content (p < 0.05). The Au × STH offspring had the highest protein content (p < 0.05). The arachidonic acid and amino acid (Asp, Ala, Ile, Leu, Lys, Thr, and essential amino acid) contents were higher in the STH sheep than in the crossbred sheep (p < 0.05). The odor activity value (OAV) analysis showed that most of the aldehydes in the Au × STH offspring had higher values. The PDK4 gene expression was positively associated with the IMF content and was negatively correlated with the linoleic acid content in the Do × STH sheep (p < 0.05). The TMEM273 gene expression was positively associated with linoleic and arachidonic acid contents and was negatively correlated with oleic and palmitic acid contents in the Do × STH sheep (p < 0.05). Discussion: The results showed the differences between the crossbred sheep and STH sheep and provided the candidate genes related to meat quality in sheep.

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Introduction: Northeast Merino (NMS) is a breed developed in Northeast China during the 1960s for wool and meat production. It exhibits excellent traits such as high wool yield, superior meat quality, rapid growth rate, robust disease resistance, and adaptability to cold climates. However, no studies have used whole-genome sequencing data to investigate the superior traits of NMS. Methods: In this study, we investigated the population structure, genetic diversity, and selection signals of NMS using whole-genome sequencing data from 20 individuals. Two methods (integrated haplotype score and composite likelihood ratio) were used for selection signal analysis, and the Fixation Index was used to explore the selection signals of NMS and the other two breeds, Mongolian sheep and South African meat Merino. Results: The results showed that NMS had low inbreeding levels, high genomic diversity, and a pedigree of both Merino breeds and Chinese local breeds. A total length of 14.09 Mb genomic region containing 287 genes was detected using the two methods. Further exploration of the functions of these genes revealed that they are mainly concentrated in wool production performance (IRF2BP2, MAP3K7, and WNT3), meat production performance (NDUFA9, SETBP1, ZBTB38, and FTO), cold resistance (DNAJC13, LPGAT1, and PRDM16), and immune response (PRDM2, GALNT8, and HCAR2). The selection signals of NMS and the other two breeds annotated 87 and 23 genes, respectively. These genes were also mainly focused on wool and meat production performance. Conclusion: These results provide a basis for further breeding improvement, comprehensive use of this breed, and a reference for research on other breeds.

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Melatonin is not only a highly effective active oxygen scavenger but also an important reproductive hormone. Melatonin has a regulatory effect on animal reproduction, especially on the ovaries. It can affect the proliferation and apoptosis of cells in follicles. However, the mechanisms of the dual antioxidation and anti-apoptosis effects of melatonin on granulosa cells are still not clear, especially in sheep. Therefore, we investigated the mechanisms of the protective effect of melatonin against oxidative damage in granulosa cells. At a concentration of 250 µmol/L, H2O2 promoted granulosa cell apoptosis; however, 10 ng/mL melatonin effectively alleviated the pro-apoptotic effect of H2O2. Furthermore, through the application of high-throughput sequencing technology, we identified 109 significantly differentially expressed genes (35 upregulated and 74 downregulated genes) involved in the protective effect of melatonin against apoptosis. The expression levels of nine related genes, i.e., ATF3, FIBIN, FOS, HSPA6, MAP3K8, FOSB, PET117, DLX2, and TRIB1, changed significantly. MAP3K8 and FOS gene overexpression impacted the protective effect of melatonin in granulosa cells; the two genes exhibited an upstream and downstream regulatory relationship. Our findings indicated that melatonin alleviated H2O2-induced apoptosis in sheep granulosa cells through the MAP3K8-FOS pathway.

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It is well known that Dorper (DP) is a full-bodied, fast-growing and high dressing percentage breed, while the production performance of Small-tailed Han sheep (STH) is not so excellent, in contrast to DP. Therefore, in this study, a comparative transcriptomic analysis of liver and muscle tissues from DP and STH breeds was carried out to find differentially expressed genes (DEGs) that affect their growth and meat quality traits. The results showed that the total number of DEGs was 2,188 in the two tissues. There were 950, 160 up-regulated and 1,007, 71 down-regulated genes in the liver and muscle, respectively. Several DEGs such as TGFB1, TGFB3, FABP3, LPL may be associated with growth and development in DP. Also, several GO terms were found to be associated with muscle growth and development, such as developmental growth (GO:0048589), and myofibril (GO:0030016). Further validation of eight genes (6 up-regulated, and 2 down-regulated) was performed using quantitative RT-PCR. These findings will provide valuable information for studying growth and development as well as meat quality traits in sheep.

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The South African Mutton Merino (SAMM), a dual-purpose (meat and wool) sheep breed, is characterized by its excellent performance on growth, carcass traits and meat quality compared to other fine-wool Merino breeds. Nowadays, the SAMM breed has been widely used to cross with commercial and indigenous fine-wool or coarse-wool breeds to improve the growth and meat performance in many countries. To date, however, little is known about the genetic basis for its prominent characteristics. In this study, whole-genome sequences of 10 SAMM were sequenced and the selection signatures were analyzed together with those of 39 Australian Merino and Chinese Merino (wool-type Merino) by FST , iHS, and XP-EHH methods. In total, 313 genes in 277 regions were identified by at least 2 methods with the signal of selection and 21 of them were identified by all three methods. We highlighted a list of interesting genes, including GHR, LCORL, SMO, NCAPG, DCC, IBSP, PPARGC1A, PACRGL, PRDM5, XYLB, AHCYL2, TEFM, AFG1L, and FAM184B, which have been shown to be involved in growth, carcass traits, and meat quality by previous studies. Herein, GHR, encoding a transmembrane receptor for growth hormone, is the most notable one. We report the first study on selection signatures analysis of SAMM at whole-genome sequence level. These results provide new insights into the genetic mechanisms underlying the growth and carcass traits in SAMM.

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Long-chain fatty acyl-CoA synthetase (ACSLs) is an essential enzyme for the synthesis of fatty acyl-CoA. ACSL1 plays a key role in the synthesis of triglycerides, phospholipids, and cholesterol esters. BACKGROUND: In the current study, triglyceride content did not increase after overexpression of the ACSL1 gene. METHODS: RNA-seq and lipid metabolome profiling were performed to determine why triglyceride levels did not change with ACSL1 overexpression. RESULTS: Fatty acyl-CoA produced by ACSL1 was determined to be involved in the diglyceride synthesis pathway, and diglyceride content significantly increased when ACSL1 was overexpressed. Moreover, the arachidonic acid (AA) content in sheep adipocytes significantly increased, and the level of cyclooxygenase 2 (COX2) expression, the downstream metabolic gene, was significantly downregulated. Knocking down the ACSL1 gene was associated with an increase in COX2 mRNA expression, as well as an increase in prostaglandin content, which is the downstream metabolite of AA. CONCLUSIONS: The overexpression of the ACSL1 gene promotes the production of AA via downregulation of COX2 gene expression.

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OBJECTIVE: The objective of this study was to compare the DNA methylation profile in the longissimus dorsi muscle between Small Tailed Han and Dorper×Small Tailed Han crossbred sheep which were known to exhibit significant difference in meat-production. METHODS: Six samples (three in each group) were subjected to the methylated DNA immunoprecipitation sequencing (MeDIP-seq) and subsequent bioinformatics analyses to detect differentially methylated regions (DMRs) between the two groups. RESULTS: 23.08 Gb clean data from six samples were generated and 808 DMRs were identified in gene body or their neighboring up/downstream regions. Compared with Small Tailed Han sheep, we observed a tendency toward a global loss of DNA methylation in these DMRs in the crossbred group. Gene ontology enrichment analysis found several gene sets which were hypo-methylated in gene-body region, including nucleoside binding, motor activity, phospholipid binding and cell junction. Numerous genes were found to be differentially methylated between the two groups with several genes significantly differentially methylated, including transforming growth factor beta 3 (TGFB3), acyl-CoA synthetase long chain family member 1 (ACSL1), ryanodine receptor 1 (RYR1), acyl-CoA oxidase 2 (ACOX2), peroxisome proliferator activated receptor-gamma2 (PPARG2), netrin 1 (NTN1), ras and rab interactor 2 (RIN2), microtubule associated protein RP/EB family member 1 (MAPRE1), ADAM metallopeptidase with thrombospondin type 1 motif 2 (ADAMTS2), myomesin 1 (MYOM1), zinc finger, DHHC type containing 13 (ZDHHC13), and SH3 and PX domains 2B (SH3PXD2B). The real-time quantitative polymerase chain reaction validation showed that the 12 genes are differentially expressed between the two groups. CONCLUSION: In the current study, a tendency to a global loss of DNA methylation in these DMRs in the crossbred group was found. Twelve genes, TGFB3, ACSL1, RYR1, ACOX2, PPARG2, NTN1, RIN2, MAPRE1, ADAMTS2, MYOM1, ZDHHC13, and SH3PXD2B, were found to be differentially methylated between the two groups by gene ontology enrichment analysis. There are differences in the expression of 12 genes, of which ACSL1, RIN2, and ADAMTS2 have a negative correlation with methylation levels and the data suggest that DNA methylation levels in DMRs of the 3 genes may have an influence on the expression. These results will serve as a valuable resource for DNA methylation investigations on screening candidate genes which might be related to meat production in sheep.