| With the increasing growth rate and feed conversion efficiency,the quality problems of chicken meat have become increasingly prominent,which is difficult to meet the growing demand of consumers for high-quality livestock products.Because of the important contribution of intramuscular fat(IMF)in improving meat quality,the regulation of IMF deposition has always been a hot topic in poultry research field.Limited by physiological characteristics and poor phenotypic accuracy,data on mechanism of IMF deposition in chicken is still limited.To further elucidate the metabolic and molecular mechanism of IMF deposition in chicken,the differences in lipid metabolism were explored between IMF selection line and control line.At the same time,highthroughput sequencing is used to identify key genes associated with IMF content.The experimental results will provide a theoretical mechanism for the quality chicken production.A total of 520 female chickens from the sixteenth generation IMF selection line(n = 256)and control line(n = 264)were randomly selected to measure the IMF content,lipid composition and fatty acid composition in breast muscle tissue.Results showed that: among the principal components of IMF,only triglyceride(TG)content was significantly higher in the IMF selection line than that in the control line(P < 0.01)and positively correlated with the IMF content.In addition,the increased proportion of long chain fatty acids,including C14:0,C16:1,C18:1n9c,may be beneficial to the synthesis of TG,which may lead to an increased IMF content in the breast muscle tissue of the IMF selection line.The population structure and selection signal were analyzed based on 60 chickens(n=30 per line)using chicken 55 K SNP chip data to confirm genetic differentiation between two lines.Then,a whole-genome resequencing work was performed in 520 female chickens from the sixteenth generation IMF selection line and control line.Whole genome association analysis(GWAS)was performed on TG trait,and a 1.657 Mb QTL were identified on chromosomes 1,including 24 SNPs significantly associated with TG content and all of which are beneficial to increase the TG content.Combing the results of GWAS and selection signals analysis,a QTL that affecting TG content was mapped in 424 Kb region(chr1:31,826,000-32,250,000)on chromosome 1.Considering the gene annotation and breast muscle developmental transcriptome data,SLC16A7 and LRIG3 was identified as a key candidate gene for the regulation of TG synthesis in chicken breast muscle tissue.Comparing the transcriptome data of breast muscle tissue from the high and low TG content chickens,the expression of SLC16A7 and genes related to fatty acid metabolism and TG esterification(ACLY、ACSL5、CD36、CITED4、ELOVL5、 ELOVL7、FABP4、FABP5、FADS2、SCD5、LPL、PLIN1、PPARG and RXRG)were significantly increased in high TG group(P < 0.05),while the genes involved in lipolysis showed significantly decreased in high TG group(P < 0.05)or no difference between two groups(P > 0.05).Based on weighted gene co-expression network analysis,SLC16A7 was co-expressed with ACSL5,CITED4,ELOVL5,ELOVL7,FABP5,FADS2,PLIN1,PPARG and RXRG.All of those genes presented a significant positive correlation with TG content,IMF content and fatty acid content(C14:0,C14:1,C16:0,C16:1 and C18:1n9c).However,there was no significant difference in the expression level of LRIG3 between the high and low TG groups,and no significant relationship was found between LRIG3 and lipid content,including TG,IMF,C14:0,C14:1,C16:1 and C18:1n9c.These results indicated that SLC16A7 was involved in regulating TG synthesis in chicken breast muscle tissue.In conclusion,SLC16A7 was identified a key regulatory gene for TG synthesis in breast muscle tissue of IMF selection line and a novel potential IMF metabolism pathway of breast muscle tissue in chickens was found in this study: SLC16A7 is co-expressed with genes related to fatty acid metabolism and lipid deposition,which may regulate the fatty acids metabolism(C14:0,C14:1,C16:0,C16:1,and C18:1n9c)to promote TG deposition. |
