解析猪12号染色体上影响肌肉脂肪酸C14:0和C16:0含量主效位点的分子机理

Fatty acid compositions have profound influences on nutrition, taste and process of pork. Dietary C14:0 and C16:0 contents have been reported to be associated with risk of cardiovascular disease in humans. Through genome wide association study (GWAS), we have identified significant loci (P < 1e-10) for longissimus muscle C14:0 and C16:0 contents in a 0-2 Mb region on chromosome 12 in both of two Chinese indigenous pig breeds: Erhualian (N=331) and Laiwu (N=305) pig populations. Based on these results, we planned to genotype ~240 SNPs in the 0-2 Mb regions and measure muscle gene expression profiles with RNA-seq for 100 pigs with extreme C14:0 and C16:0 phenotypes from the two Chinese indigenous breeds. We aim to fine map the loci by examining the common significant associations in the two Chinese indigenous pig breeds, prioritize causal genes by integrating the eQTL mapping results, and characterize the key genes and gene networks associated with C14:0 and C16:0 contents using gene coexpression network analysis. The findings would provide important insights into genetic loci influencing C14:0 and C16:0 contents in pork, and facilitate utilization of Chinese indigenous pig breeds to improve pork nutrition.

脂肪酸组成是影响猪肉营养、风味和加工的重要指标。食物中饱和脂肪酸C14:0和C16:0含量高会增加人心脑血管疾病风险。通过全基因组关联分析，申请人同时在二花脸（N=331）和莱芜（N=305）两个中国地方猪群体中，发现12号染色体0-2 Mb区间内存在显著影响（P < 1e-10）背最长肌C14:0和C16:0含量的位点。基于这些结果，项目组拟在12号染色体0-2 Mb关键区域内开发240个SNP标记，检测两个地方猪群体中共100个表型极端个体240个SNPs基因型和肌肉RNA-seq转录组。通过搜寻两个地方猪群体共有显著信号来精细定位，结合基因表达QTL分析，确定因果基因。通过基因表达网络分析，揭示与C14:0和C16:0含量相关联的关键基因和基因网络。预期结果将进一步加深人们对猪肌肉脂肪酸代谢分子机理的理解，并为中国地方猪种健康猪肉的开发利用提供重要基因位点。

本研究在原有数据基础上，进一步检测了巴马香猪（个体数315）和嵌合家系群体（个体数1500）共2300份肌肉或脂肪组织的脂肪酸组成表型。将实验室的研究资源扩充到7个群体，5000余份样本。通过高密度SNP芯片和全基因组序列填充技术，增加了相关群体的遗传标记密度。整合六个群体的表型和基因型数据，开展了全基因关联分析和荟萃分析。进一步精细定位了ELOVL6，SCD和FASN位点，将FASN位点的置信区间定位在300kb以内。通过单倍型分析结果表明FASN位点虽然在莱芜和二花脸猪群体均检测到信号，但是两个群体可能不共享因果突变。通过遗传相关分析，发现FASN位点对胴体，背膘厚和肌内脂肪含量的影响效应均不显著，说明该位点用于标记辅助育种不会影响其他经济性状。转录组数据显示FASN主要是在脂肪组织中高量表达，FASN肝脏，肌肉和脂肪表达水平与C14:0含量都不显著相关，表明该位点可能通过转录后的调控机制发挥作用。虽然没有鉴定到因果突变，但是本研究的结果具有育种价值。后续计划继续对二花脸群体进行重测序，并对FASN基因进行转录后修饰和翻译水平的验证工作。