| At present, excessive fat deposition is one of the main problems encountered by the duck industry, which makes feed utilization decrease and carcass quality decline. More importantly, that the diseases caused by excessive intake of fat-related has aroused widespread interest, and to some extent, it restricted the duck industry. Fat deposition, as a quantitative trait, is regulated by multi-gene. However, the current reported studies are still lacking in duck fat deposition related to candidate genes, and further research is very necessary. In this study, 4 populations, Cherry Valley duck, Jinding duck, White Muscovy, and Sumu Sheldrake (10w) were used. The fatty acid content of breast muscle and 9 Serum biochemical parameters, including triglyceride (TG), total cholesterol (TC), albumin (Alb), total protein (TP), cholinesterase (ChE), alkaline phosphatase (ALP), immunoglobulin A (IgA), globulin (GLO) and Alb/GLO ratio were determined and evaluated by GC-MS and Blood Automatic Biochemical Analyzer. LXRαgene was cloned from Cherry Valley and White Muscovy by using RT-PCR method, and it's structure and function were further predicted by bioinformatics. Genetic variation of LXRα, Adiponectin, and ApoVLDL-II genes and its relationship with meat quality traits in 4 populations were studied by using PCR-SSCP and DNA sequencing. Real fluorescent quantitative PCR was conducted to investigate expression pattern of LXRα, Adiponectin, and ApoVLDL-II genes in 12 tissues (heart, liver, chest muscle, small intestine, large intestine, cerebellum, brain, hypothalamus, kidney, lung, spleen and proventriculus) of 10-week-old Jinding duck and the developmental expression pattern in liver of White Muscovy and Jinding duck at different developmental stages (0d, 2w, 4w, 6w, 8w and 10w). Probably, the achievement of this study will contribute to duck breeding or genetic improvement and provide reasonable scientific ground. The main results were showed as following:1. Analysis of fatty acid content in breast muscle of duck 16 fatty acids were detected in each duck population, among which oleic acid (C18: 1), palmitic acid (C16:0), stearic acid (C18:0) and linoleic acid (C18:2) were the main composition, accounted for 95% or so. Fatty acids content were distinct from each other among populations, and all fatty acids except C14:1 (P>0.05) exhibited population effect, and C15: 0 was significant (P<0.05) and the rest showed extremely significant population effect (P<0.01). No fatty acid existed sex effect, and the population and sex interaction effect existed (P>0.05). UFA of Cherry Valley duck was the highest, whereas PUFA and EFA were the lowest, however, White Muscovy just the opposite.2. Analysis of serum biochemical parameters The 9 serum biochemical parameters of all populations exhibited a very significant population effect (P<0.01), among which TG showed a significant sex effect (P<0.05), and TC and ALP presented significant sex effect (P<0.01), and TG, TC, and ALP of the male was significantly higher than the female (P<0.05); The interaction effect for TG and TC between population and sex was significant (P<0.01).3. LXRαgene cloning and bioinformatics LXRαgene cDNA was cloned, whose size was 1626 bp, in Cherry Valley Duck and White Muscovy for the first time, and GenBank accession number were FJ966078 and GU132847 respectively. It embraces 5'-UTR sequence of 73 bp, CDS all sequence of 1230 bp and 3'-UTR sequence of 323 bp, and encoded 409 amino acids. There were 14 nucleotides (9 CDS and 5 UTR) and 3 amino acids (Ser163Gly, Gln171Glu and Asn361Lys), which were different between these 2 populations. LXRαprotein in duck had 74-78% homology with mammals and fish, and up to 97% with chicken. Cluster analysis revealed that probably mammals, birds and fishes, each of these belonged to different categories separately. Bioinformatics analysis indicated that duck LXRαprotein contained 17 phosphorylation sites, two low compositional complexity region, a ZnF-C4 and a HOLI domain, without signal peptide and transmembrane helix; The diversity of CDS and the structure of amino acids in 2 LXRαgenes resulted in the RNA folding, protein secondary structure and O-glycosylation sites differences.4. Associations of genetic variations of LXRαgene with meat quality traits in duck It was the first time that silent mutation 277(C/G) was identified in LXR-E5 locus, and 1396(G/C) mutation and 44(C/T) mutation were found in LXR-E12 locus and LXR-I6 locus of duck LXRαgene respectively. Other 6 loci (LXR-E4, LXR-E6, LXR-E7, LXR-E8, LXR-E10 and LXR-E11) had no polymorphism. Correlation analysis showed that LXR-E5 locus of LXRαgene significantly associated with tenderness (P<0.05), and LXR-E12 and LXR-I6 loci were significantly related to pH, water loss rate, IMF, TC, TG, UFA , PUFA and EFA (P<0.05). Interaction between LXR-E5 and LXR-I6 loci had a significant impact on UFA (P<0.05), and that BBCC genotype was the highest. Interaction between LXR-E12 and LXR-I6 loci had an extremely significant effect on tenderness, pH, and TC (P<0.05), and that ABCC, BBDD, and BBDD were the highest respectively.5. Associations of genetic variations of LXRαgene with meat quality traits in White Muscovy There were 53(G/A) and 1483(-/T) mutations first found in LXR-E4 and LXR-E12 loci of White Muscovy LXRαgene respecticely. There were no polymorphism in other 7 loci(LXR-E5,LXR-E6,LXR-E7,LXR-E8,LXR-E10, LXR-E11 and LXR-I6). Correlation analysis suggested that LXR-E4 locus had a significant genetic effect on IMF, UFA and meat color (P<0.05). Interaction between LXR-E4 and LXR-E12 loci had a significant effect on UFA (P <0.05), and that BBCC was the highest.6. Associations of genetic variations of adiponectin gene with meat quality traits in duck 15 SNPs were discovered in 4 loci of ADP1, ADP2, ADP3 and ADP4 of duck adiponectin gene, of which G887A of 3'-UTR, 12 SNPs (C86T, C104T, C146T, C155T, C456T, A574G, C651T, C684T, T768C, G784A, A801C and C807T) of CDS, C273T and C295T of intron 2. A574G, G784A, and A801C were missense mutations, resulting in amino acid sequence altered, that were 144 of Thr(T) into Ala(A), 214 of Ile(I) into a Val(V), and 219 of Asp(D) into Glu(E). Association results showed that ADP1 locus of duck adiponectin gene presented significant genetic effects on IMF, UFA, PUFA and EFA (P<0.05). ADP2 locus showed significant genetic effects on water loss rate, IMF, TC, and UFA (P<0.05). ADP4 locus conducted significant genetic effect on water loss rate, TC, UFA and PUFA (P<0.05). Interactions between ADP1 and ADP3, and ADP2 and ADP3 had a significant influence on UFA (P<0.05), and genotypes of AACC and CDBC were the highest respectively. Interactions between ADP1 and ADP4, and ADP3 and ADP4 on water loss rate and IMF appeared a significant effect (P<0.05), and genotypes of CDAC and CCBB for water loss rate, and DDAA and CCAA for IMF were the highest, respectively.7. Associations of genetic variations of adiponectin gene with meat quality traits in White Muscovy 3 SNPs were first found in White Muscovy adiponectin gene, including A167G and G711A of CDS, and C290T of intron, which were nonsense mutations. ADP1 and ADP2 loci of adiponectin gene conducted significant effect on water loss rate and IMF (P<0.05). Interactions between ADP1 and ADP4, and ADP2 and ADP4 on UFA appeared a significant influence (P<0.05), and genotypes of BBFF and TTFF showed the highest respectively. 8. Associations of genetic variation of ApoVLDL-II gene with meat quality traits in duck Genomic DNA sequence(GQ 180104) of duck ApoVLDL-II were first cloned, and 5 loci of Exon1, Exon2, Exon3, Exon4 and Intron1 were detected by PCR-SSCP. There were no polymorphism in Exon1 and Exon2, whereas 12 SNPs (T667C, C669G, T673C, G674A, G683A, G688A, C708G, T715G, G2106A, T2723C, C2743T, and A2944C), and insertion/deletion TG and CC after the 764 bp and 1910 bp respectively were discovered in another 3 loci. In addition to A2944C mutation located in exon 4 UTR, others were in introns, and the complete coding region mutation was not detected. Correlation analysis showed that Exon3 and Exon4 loci had significant genetic effects on water loss rate, tenderness, IMF, UFA, PUFA and EFA (P<0.05), and Intron1 locus had a significant genotype effect on the pH, water loss rate, IMF, TC, TG and UFA (P<0.05). Interactions between Exon3 and Exon4 had a significant impact on TC (P<0.05), and the genotype of CCBB presented the highest. Interactions between Exon3 and Intron1 had a significant influence on UFA (P<0.05), and the genotype of DDBB was the highest.9. Associations of genetic variation of ApoVLDL-II gene with meat quality traits in White Muscovy Genomic DNA sequence (GQ 180103) of White Muscovy ApoVLDL-II gene was first discovered. Only Exon3, Exon4 and Intron1 of 5 loci exhibited polymorphism, while exon 3 occured T1986C was silent mutation, C2901T mutation was detected in UTR of exon 4, and A720G mutation and insertion/deletion 13bp sequence AAAATCTTGTTTA after the 687bp was discovered in intron1. Association analysis suggested that Intron1 had a significant genetic effect on IMF and the TG in White Muscovy (P<0.05). Interactions between Exon3/Exon4 and Intron1 exhibited no significant impact on all traits detected (P>0.05).10. Tissue expression pattern analysis of LXRα, Adiponectin, and ApoVLDL-II genes By real-time fluorescent quantitative PCR, the results revealed that LXRαgene in Jinding duck given the performance of highly specific expression of liver, and then lung, spleen, kidney, heart and hypothalamus showed moderate expression, and last chest muscle, cerebellum, brain, proventriculus, small intestine and large intestine presented low expression. Developmental expression pattern of LXRαgene in liver of Jinding duck was in agreement with White Muscovy, performing that the level from 0-day-old dropped to 2 weeks, and then gradually increased, and male was lower than female. Regardless of male or female, levels of expression of White Muscovy were lower than Jinding duck during various periods. Adiponectin gene performed highly specific expression in Jinding duck breast muscle, intestine and heart, and showed moderate expression in lung, liver, small intestine, spleen and kidneys, presented low expression in proventriculus, hypothalamus, cerebellum and brain. With age increasing, level of Adiponectin gene expression decreased in male and female. However, male showed higher than female at different phases. 0-day-old to 4-week-old male and female Jinding duck was higher than White Muscovy, whereas 6-10 weeks lower. The sharpest decline for Jinding duck was the 4-6 weeks, while the 6-8 weeks for White Muscovy. ApoVLDL-II gene expression level in liver of the male had shown a slow decline, whereas a slowly rising for the female, indicating that sex affects ApoVLDL-II gene expression, and may play a special biological role in diferent genders.11. Associations of LXRα, Adiponectin and ApoVLDL-II genes expression and regulation Analysis of gene expression and regulation of 3 genes in Jinding duck and White Muscovy reveled that they positively regulated with each other in liver tissue of male during 0 day to 2 weeks, but in female, ApoVLDL-II negatively regulated by LXRαand Adiponectin, and LXRαand Adiponectin presented a positive control. During 4-10 weeks of age, LXRαwas negatively regulated by ApoVLDL-II and Adiponectin, while ApoVLDL-II and Adiponectin gene was up-regulated relationship in male; Adiponectin gene was negatively controlled by ApoVLDL-II and LXRα, while there was the up-regulated relationship between ApoVLDL-II and LXRαgene in female. Results of synergistic expression analysis showed that: There were sex differences in gene expression and regulation of 3 genes.
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