脂肪酸合成酶基因(FASN)的研究进展

在哺乳动物中,脂肪酸合成酶在脂肪酸合成中起着至关重要的作用。它含有7个活性位点,在还原型辅酶Ⅱ的存在下,FASN负责乙酰辅酶A(acetyl-CoA)和丙二酰辅酶A(malonyl-CoA)从头合成一种长链软脂酸(棕榈酸酯)的所有催化步骤。脂肪酸合成酶是脂肪合成的关键酶,并且在腹脂肪组织重变异及相关性状变异中起着重要作用。综述了FASN及其基因在生命活动中的地位、作用、定位、结构及FASN基因的遗传变异与生产性状关系的研究进展。     

Hepatic Lipogenesis Associated with Biochemical Changes in Overfed Landaise Geese and China Xupu Geese

This experiment studied hepatic lipogenesis associated with biochemical changes in overfed Landaise Geese and China Xupu geese. Twenty healthy male Landaise geese and 20 healthy male Xupu geese, hatched on the same day under the same feeding conditions, were selected as experimental animals. The animals were divided into two groups and each breed served as an experimental group. Per goose of per experimental group served for a repeat. Brown rice was selected as test diet. After overfeeding for 21 d and then slaughtering, the biochemical changes of hepatic lipogenesis in the genetic susceptibility to fatty liver were evaluated. These results showed that （1） the weight of fatty liver of the two breeds of geese were 801 and 375 g （P〈0.05）, respectively. There were no differences on the abdominal fat pat, filet total and filet pectoralis major in the two breeds experimental of the geese group （P〈0.05） and no difference on body and filet skin plus subcutaneous adipose tissue （P〉0.05） was found; （2） in these two breeds of geese, there were no differences on very-lowdensity lipoprotein （VLDL）, cholesteryl esters （CE） （P〈0.05）, free cholesterol （FC）, triglycerides （TG）, phospholipids （PL） and protein （P 〈 0.05）; （3） there were no differences on activities of malic enzyme （ME）, glucose-6-phosphatedehydrogenase （G6PDH）, acetyl-CoA-carboxylas （ACX）, fatty acid synthase （FAS）, and mRNA level of ME in the two experimental breeds of geese groups （P 〈0.05）; （4） test in Landaise geese group showed that there was no significant correlation with the specific enzymatic activities, while in Xupu geese group, the liver weight was negatively correlated to the specific activity of ACX and positively to that of ME; （5） in these overfed geese, ME activity appeared to be a major factor involved in the genetic susceptibility to hepatic steatosis and it determined the hepatic lipogenesis capacity.     

投喂蚕豆对草鱼肝脏脂肪蓄积及脂肪代谢的影响

为了研究摄食蚕豆后草鱼(Ctenopharyngodon idellus)肝脏脂肪蓄积情况以及形成原因,采集了摄食蚕豆的草鱼(试验组)和摄食配合饲料的草鱼(对照组)的肝脏样本后,通过HE染色、油红O染色和透射电镜分别对两组草鱼肝脏进行病理学特征、脂质蓄积情况和肝细胞的超显微结构观察,同时检测与脂肪代谢相关的生理生化指标,并分析与脂肪酸合成相关的基因表达情况。结果发现:与对照组草鱼相比,试验组草鱼肝脏发生明显的脂肪变性,线粒体形态异常且数量减少;试验组草鱼血清中甘油三脂(TG)、总胆固醇(TC)、低密度脂蛋白胆固醇(LDL-C)、谷丙转氨酶(ALT)和谷草转氨酶(AST)含量显著升高(P0.05);试验组草鱼肝脏中TG、TC和过氧化氢(H_2O_2)含量显著增加,但过氧化氢酶(CAT)和谷胱甘肽(GSH)显著降低(P0.01);试验组草鱼肝脏脂肪酸合成相关基因(acc和fas)的mRNA表达量极显著高于对照组(P0.01)。研究表明,长期摄食蚕豆的草鱼肝脏会发生脂肪变性,其可能与脂肪酸从头合成(DNL)增加、氧化应激增强及线粒体结构破坏等有关。研究结果将为脆肉鲩营养调控和预防鱼类肝脏脂肪变性提供一定的理论依据。     

坦布苏病毒感染诱导雏鸭体内未折叠蛋白反应

[目的]检测坦布苏病毒在雏鸭体内诱导未折叠蛋白反应的信号通路(PERK、IRE1和ATF6),为揭示坦布苏病毒致病机制提供理论基础.[方法]取1日龄SPF雏鸭,腹腔接种坦布苏病毒(JS804株),于接种后12、24、36和48 h从对照组和攻毒组各取5只剖杀,分别取肝脏、心脏和脑组织,利用组织总RNA提取试剂盒提取各个...     

Effective Application of Nutritional Practices in Preventing Dairy Cow Fatty Liver

Fatty liver in dairy cows, which is associated with decreased metabolic function of the liver, develops during times of elevated non-esterified fatty acid （NEFA） concentrations in the blood when the hepatic uptake of lipids exceeds the oxidation and secretion of lipids by the liver and then it will cause hepatic accumulation of triglyceride （TG）. The condition is often related to decreased health status, well-being, productivity, and reproductive performance of cows. Prevention of fatty liver in the transition period is always better than any treatments. The nutritional preventative strategies mainly focus either on decreasing the supply of NEFA to liver, and it aims to improve liver function or optimize the capacity then to dispose of NEFA by exporting them as triglycerides in lipoproteins （VLDL）. Good dry cow nutritional programs, combined with excellent feeding management to achieve high levels of dry matter intake throughout the transition period should be the first priority for management. Several different compounds can promote these metabolic actions. The addition of glucose precursors such as glycerol, propyelene glycol, or propionate salts to the feed in the transition diet can modify metabolism in a manner to decrease fatty acid mobilization from adipose tissue and reduce the likelihood of liver TG accumulation. Supplying some other specific nutrients to dairy cows during the transition period may increase rates of NEFA disposal, with resulting effects on performance, though the hepatic capacities for export as triglycerides within VLDL are relatively limited in ruminants. Further studies examining nutritional and management strategies are required to develop new preventive or treatment options that are more practical to reduce the occurrence of fatty liver and its adverse metabolic effects.     

FGF19 as a postprandial, insulin-independent activator of hepatic protein and glycogen synthesis

Fibroblast growth factor (FGF) 19 is an enterokine synthesized and released when bile acids are taken up into the ileum. We show that FGF19 stimulates hepatic protein and glycogen synthesis but does not induce lipogenesis. The effects of FGF19 are independent of the activity of either insulin or the protein kinase Akt and, instead, are mediated through a mitogen-activated protein kinase signaling pathway that activates components of the protein translation machinery and stimulates glycogen synthase activity. Mice lacking FGF15 (the mouse FGF19 ortholog) fail to properly maintain blood concentrations of glucose and normal postprandial amounts of liver glycogen. FGF19 treatment restored the loss of glycogen in diabetic animals lacking insulin. Thus, FGF19 activates a physiologically important, insulin-independent endocrine pathway that regulates hepatic protein and glycogen metabolism.     

植物油脂合成调控与遗传改良研究进展

植物种子油脂储存的主要形式是三酰甘油。在植物生长发育中,脂肪酸和三酰甘油具有重要功能。分析了植物种子油脂合成代谢过程调控研究进展,总结了改良植物种子油脂策略：①调节碳源分配,抑制碳源流入蛋白质合成路径的关键酶编码基因的表达、增强碳源流入脂肪酸合成路径的关键酶编码基因的表达;②干预油脂合成,促进脂肪酸生物合成,提高三酰甘油组装过程的关键酶编码基因的表达水平;③提高种子油脂的品质：改变植物脂肪酸组成,调节脂肪酸脱氢酶基因的表达,引入外源超长链多不饱和脂肪酸合成途径;④调控油脂合成代谢途径的转录因子表达,提高种子油脂含量。还讨论了植物油脂合成的三酰甘油前体转运机制及合成途径多基因共同调节合成途径等。     

ITGB1基因表达与鹅肥肝形成的关系

为探究ITGB1基因与鹅肥肝形成的关系,选取30只70日龄健康朗德公鹅,随机分为填饲组与对照组并进行24 d填饲.运用ITGB1基因序列进行生物信息学分析,采用RT-qPCR技术检测不同填饲阶段(填饲12d与24d)鹅肝脏中ITGB1基因的表达水平,同时,使用不同剂量的脂肪肝形成相关因子(胰岛素、葡萄糖、油酸、亚油酸和棕榈酸)处理鹅原代肝细胞,检测ITGB1基因的表达水平.结果 发现:全长CDS共2418 bp,编码805个氨基酸,与鸭的同源性高于98％,可编码1种亲水性蛋白;与对照相比,填饲12d与24 d时,鹅肝脏中ITGB1基因的表达均显著上调(P＜0.05);0.5 mmol·L-1油酸、亚油酸和棕榈酸均能显著地诱导鹅原代肝细胞中ITGB1基因上调(P＜0.05);200mmol·L-1葡萄糖能极显著地诱导鹅原代肝细胞中ITGB1基因上调(P＜0.01);此外,0.2 mmol·L-1胰岛素也能在一定程度上有诱导其表达上调的趋势(P=0.098).结果 表明,ITGB1基因表达上调与鹅肥肝形成密切相关,受脂肪肝形成相关因子诱导,提示ITGB1基因表达上调可能会促进鹅肥肝的形成.     

植物脂肪酸合成及其在基础抗性和生物固氮中的作用研究进展

综述了植物脂肪酸合成、酰基载体蛋白在脂肪酸合成中的作用、脂肪酸在基础抗性和生物固氮中的作用,旨在为植物遗传育种及脂肪酸合成及功能相关分子机制研究提供参考。     

乌金猪与长白猪肝脏脂肪代谢相关基因mRNA表达水平的比较研究

 为探讨不同品种猪体内脂肪代谢的差异,本文选用云南本土的脂肪型猪种乌金猪与外源性的瘦肉型猪种长白猪为研究对象,通过实时荧光定量PCR比较研究了9个脂肪代谢相关基因mRNA在二者之间肝脏表达的差异,结果显示：乌金猪肝脏组织脂肪酸合成酶（FAS）基因的mRNA表达水平极显著高于长白猪（P<0.01）,乙酰辅酶A羧化酶（ACC）、固醇元件结合蛋白（SREBP）、苹果酸酶（ME）和载脂蛋白B（ApoB）基因的mRNA表达水平显著高于长白猪（P<0.05）,肉碱脂酰转移酶-1（CPT1）基因的mRNA表达水平极显著低于长白猪（P<0.01）,酰基辅酶A氧化酶(ACOX)基因的mRNA表达水平显著低于长白猪（P<0.05）,二酰基甘油酰基转移酶1（DGAT1）和过氧化物酶体增殖物激活型受体α（PPARα）基因的mRNA表达水平与长白猪无显著差异（P>0.05）。本研究结果表明,乌金猪肝脏脂肪合成和脂肪酸转运相关基因的表达水平高于长白猪,而脂肪分解相关基因的表达水平低于长白猪,乌金猪肝脏的脂肪合成能力较长白猪强。     

TRB3 links the E3 ubiquitin ligase COP1 to lipid metabolism

During fasting, increased concentrations of circulating catecholamines promote the mobilization of lipid stores from adipose tissue in part by phosphorylating and inactivating acetyl-coenzyme A carboxylase (ACC), the rate-limiting enzyme in fatty acid synthesis. Here, we describe a parallel pathway, in which the pseudokinase Tribbles 3 (TRB3), whose abundance is increased during fasting, stimulates lipolysis by triggering the degradation of ACC in adipose tissue. TRB3 promoted ACC ubiquitination through an association with the E3 ubiquitin ligase constitutive photomorphogenic protein 1 (COP1). Indeed, adipocytes deficient in TRB3 accumulated larger amounts of ACC protein than did wild-type cells. Because transgenic mice expressing TRB3 in adipose tissue are protected from diet-induced obesity due to enhanced fatty acid oxidation, these results demonstrate how phosphorylation and ubiquitination pathways converge on a key regulator of lipid metabolism to maintain energy homeostasis.     

丙型肝炎病毒NS4B蛋白调控Hep3B细胞非折叠蛋白质反应研究

研究表达的丙型肝炎病毒(HCV)NS4B对Hep3B细胞非折叠蛋白质反应的影响。NS4B重组真核表达质粒pcDNA3.1(-)NS4B通过脂质体转染Hep3B细胞,G418筛选和Western blot鉴定稳定转染细胞;RT-PCR检测稳定转染细胞内XBP1 mRNA剪接,Western blot鉴定ATF6蛋白切割,荧光素酶试验检测稳定转染细胞内GRP78和XBP1启动子活性。G418筛选和Western Blot鉴定证实获得稳定表达NS4B的Hep3B细胞;在该细胞内,XBP1 mRNA剪接、ATF6切割、XBP1和Grp78启动子激活均被检测到。NS4B在Hep3B的稳定表达诱导了非折叠蛋白质反应。     

缺刻缘绿藻Δ15脂肪酸去饱和酶的功能分析

缺刻缘绿藻（Myrmecia incisa Reisigl）是一种富含多不饱和脂肪酸的球形单细胞淡水绿藻。在脂肪酸合成途径中,脂肪酸去饱和酶与脂肪酸酰基结合载体结合进行脂肪酸去饱和反应。为探究与缺刻缘绿藻中?15脂肪酸去饱和酶（fatty acid desaturase,FAD）结合的脂肪酸酰基结合载体,选用酿酒酵母（Saccharomyces cerevisiae）INVSc1和聚球藻（Synechococcus sp.）PCC7942分别验证?15 FAD与酰基辅酶A（酰基-CoA）或酰基载体蛋白（酰基-ACP）结合的脂肪酸去饱和过程。根据缺刻缘绿藻的?15 FAD基因构建双源表达载体pYES2-?15 FAD和pCAMBIA1300-?15 FAD,通过电穿孔法将重组表达质粒分别转入酿酒酵母INVSc1和聚球藻PCC7942中,筛选得到转基因菌株。取相同细胞数的转基因酵母和转基因聚球藻,培养时分别添加等量的底物亚油酸（linoleic acid,18:2?9,12,LA）,以LA作为酰基受体,使其进入转基因酵母和转基因聚球藻的生物合成途径中,培养36-72 h。利用气相色谱-质谱联用系统对总脂肪酸的各组分进行分析,结果显示,在转基因实验组中检测到LA和?-亚麻酸（?-linolenic acid,18:3?9,12,15 ,ALA）的存在,空白实验则未检测出相应的产物。通过计算,转基因酵母催化LA生成ALA的效率29.31%,转基因聚球藻催化底物LA生成ALA的效率为30.86%。根据结果证明无论是酰基-ACP还是酰基-CoA,与缺刻缘绿藻中的?15 FAD结合进行反应的效率相近,不存在偏好性,由于?15 FAD是特异性蛋白,因此证明缺刻缘绿藻中的?15 FAD属于脂酰基结合蛋白。     

The Later Effects of DHA in Diet on Regulating Transcription of Lipid Genes of Broiler

The effect of docosahexaenoic acid (DHA) on lipid metabolism in broiler were studied in order to p rovide test results for polyunsaturated fatty acids (PUFA) regulating fatty deposition, 1-wk-old Arbor Acres (AA) broiler were fed with DHA microalgae and slaughtered after 2 wk. The tissues were stored for isolating total RNA. RT-PCR was used to analyze the expression changes of genes. DHA microalgae significantly increased average body gain and feed conversion rates, reduced the levels of total cholesterol (TC), total glycerin (TG), and low-density lipoprotein cholesterol (LDL-C) in serum and increased the content of high-density lipoprotein cholesterol. 1 wk later, the effects were still remained. In liver tissue, DHA microalgae increased the expression of PPARα and carnitine palmitoyltransferase-1 (CPT-1). 1 wk later, it was observed that DHA up-regulated the expression of fatty acid synthase (FAS), acetyl CoA carboxylase (ACC), lipoprotein lipase (LPL) and carnitine palmitoyltransferase-1 (CPT-1). 2 wk later, it still increased the expressions of FAS and CPT-1, but a converse result was observed for ACC and LPL. In adipose tissue, DHA microalgae suppressed the expression of PPARα and LPL, up-regulated the expression of ACC, FAS, and CPT-1. After withdrawal, the expression of genes in test group was significantly lower than that in control group (P＜0.01). In the muscle of chest, DHA microalgae significantly inhibited the gene expression (P＜0.01). 1 wk later, the expressions of FAS, LPL and CPT-1 in test group were significantly higher than that in control group (P＜0.05). 2 wk later, it was shown that DHA significantly inhibited fat synthesis and decomposition. In the leg, there was not any PPARα expression being detected, probably because of the less expression in muscle tissues or the regulation of PPARα had no relation to the case. DHA microalgae promote fat synthesis in the liver and inhibit in adipose and muscle tissues. It still has effects after 1 wk of withdrawal.     

腺苷甲硫氨酸对成肌细胞成脂分化及脂肪沉积的影响

【目的】以小鼠成肌细胞（C2C12）为模型探讨蛋氨酸代谢产物腺苷甲硫氨酸（S-adenosylmethionine,SAM）对肌肉来源的多能干细胞成脂分化及脂肪沉积的影响。【方法】分别用含有0、0.25、1.0和2.0 mmol•L-1 SAM的培养基处理细胞,在处理后的0、24、36和48 h分别对各处理组细胞进行油红O染色观察细胞形态并测定光密度（OD）值;在处理后第2天收集细胞总RNA与总蛋白,分别用RT-PCR和western blotting方法检测细胞成脂相关基因的mRNA与蛋白表达水平。【结果】经SAM处理后,细胞表现出脂肪细胞的形态特征;细胞内脂肪沉积水平上升,并且随SAM处理浓度的升高呈现出剂量依赖效应;细胞的脂肪特异性基因PPARγ、C/EBPα的mRNA及蛋白表达水平显著升高（P＜0.05）;其它特异性基因aP2、FAS及SREBP-1的表达在经SAM处理后呈剂量依赖性升高（P＜0.05）,其中2.0 mmol•L-1 SAM处理组升高最为显著,三者mRNA表达水平分别上升了6.86（P＜0.01）、3.45（P＜0.05）和3.48（P＜0.01）倍。【结论】SAM可以促进C2C12细胞成脂分化及细胞内脂肪的沉积。     

饲料中胆汁酸对红鳍东方鲀脂肪酸组成及抗氧化能力的影响

为研究饲料中添加胆汁酸对红鳍东方鲀脂肪酸组成及抗氧化能力的影响,以鱼油为主要脂肪源,配制五种等氮饲料,以初始体重14g的红鳍东方鲀进行为期56天的投喂养殖实验。设置适宜脂肪含量(8%)的对照组,并在对照组添加0.02%及0.10%的胆汁酸,分别获得低胆汁酸添加组(BA)和高胆汁酸组(HBA)。另设一高脂组(脂肪含量12.5%,HL组)及高脂+0.02%胆汁酸组(HLBA组)。结果表明,添加胆汁酸的处理组肌肉和肝脏MUFA均低于对照组,其中HBA组显著低于对照组(P<0.05)。肌肉中n-6PUFA含量在HLBA和HL组显著低于其他组(P<0.05)。在适宜脂肪含量的三个处理组间,肝脏中的C20:0、C16:1n-7、C18:1n-9、C18:2n-6、C20:4n-6、C18:3n-3、C18:4n-3、C20:5n-3和C22:6n-3都呈现随着胆汁酸添加量增加而降低的趋势。血清超氧化物歧化酶活性和谷胱甘肽过氧化物酶活性都有随着胆汁酸添加而升高的趋势,且在高脂组显著高于对照组(P<0.05);血清谷胱甘肽还原酶则呈现相反的趋势。肝脏中谷胱甘肽过氧化物酶1的mRNA相对表达量在对照组显著高于其他组,而BA组氧化还原酶1的基因表达量显著高于对照组;在高脂组添加胆汁酸显著升高了过氧化氢酶的基因表达量。综上所述,饲料中胆汁酸的添加降低了饲料及鱼体组织中一系列长链脂肪酸的含量;胆汁酸对血清抗氧化蛋白活性的影响与其对肝脏抗氧化相关基因表达的影响结果不一致。     

小鼠肝再生过程中脂质代谢相关通路中基因的表达谱变化

[目的]研究肝再生过程中肝脏内脂质代谢通路相关基因的表达谱变化。[方法]建立CC l4诱导肝再生小鼠模型,从小鼠肝组织中提取总RNA,通过微阵列基因芯片技术检测在不同肝再生期间脂质代谢通路相关基因的表达变化,并进行具体功能分析。[结果]肝再生过程中,有98个脂质代谢相关基因的表达水平发生了变化,根据这些基因表达的变化趋势可以分为8组。整体上看,基因表达前期表现为抑制,后期表现为上调。其中,脂肪酸的合成通路基因表达以上调为主,分解代谢通路变化并不明显;大多数胆汁酸合成通路基因在4.5天之前表现为抑制,在4.5天和7天时表现为上调。[结论]肝再生过程中,脂质代谢相关通路间的基因表达变化并不一致,这些数据为进一步研究脂质代谢相关通路对肝再生的调控作用提供了明确的基因范围。     

胆碱对鹅体内脂质代谢及肝脏FAS基因mRNA表达的影响

【目的】探讨胆碱对青农灰鹅体内脂质转运、代谢的作用及脂肪酸合成酶FAS（fatty acid synthase）基因表达的影响,确定鹅日粮中胆碱的最适添加量。【方法】将180只1日龄青农灰鹅随机分为6个处理组,每处理组3个重复,每个重复10只。试验在玉米-豆粕型饲粮的基础上各组的胆碱添加量分别为0、600、1 200、1 800、2 400和3 000 mg•kg-1,试验期15周。屠宰后测定肝脏和血清总胆固醇、甘油三酯,血清低密度脂蛋白胆固醇、高密度脂蛋白胆固醇、葡萄糖、胰岛素、胰高血糖素水平,肝脏脂蛋白酯酶、肝脂酶及血清胆碱酯酶活性和肝脏脂肪酸合成酶（FAS）基因表达量。【结果】①4周龄时,饲粮中添加胆碱显著降低肝脏和血清总胆固醇、甘油三酯、血清低密度脂蛋白胆固醇、胰岛素水平和血清胆碱酯酶活性（P＜0.05或P＜0.01）;显著提高肝脏脂蛋白酯酶、肝脂酶活性和血清胰高血糖素水平（P＜0.05）;但对血清高密度脂蛋白胆固醇、葡萄糖含量影响不显著（P＞0.05）。15周龄时,饲粮中添加胆碱显著降低肝脏和血清总胆固醇、甘油三酯、低密度脂蛋白胆固醇含量与胰岛素水平及血清胆碱酯酶活性（P＜0.05或P＜0.01）;显著提高肝脏脂蛋白酯酶、肝脂酶活性和血清高密度脂蛋白胆固醇、胰高血糖素水平（P＜0.05）;但对血清葡萄糖含量影响不显著（P＞0.05）。②饲粮中添加胆碱显著提高肝脏FAS基因的表达量（P＜0.01）,且肝脏脂肪酸合成酶基因表达量随胆碱添加水平呈先下降后上升趋势。【结论】综合考虑胆碱对鹅肝脏脂质代谢的影响,1—4和5—15周龄鹅饲粮中胆碱适宜添加量分别为1 200—1 800和1 200 mg•kg-1。     

奶山羊SCD基因CDS区的克隆、序列分析及过表达

【目的】研究奶山羊硬脂酰辅酶A去饱和酶基因（stearoyl-CoA desaturase,SCD）在乳腺上皮细胞中对不饱和脂肪酸合成过程相关基因的调控及对细胞脂肪酸组成的影响。【方法】用RT-PCR方法从西农萨能羊乳腺组织中扩增SCD基因,进行序列分析和组织表达谱分析;构建重组腺病毒质粒,进行包装和扩增后,感染体外培养的奶山羊原代乳腺上皮细胞,实时定量检测相关基因的表达,western blotting检测蛋白变化,气相色谱-质谱联用分析细胞内脂肪酸组成变化。【结果】①获得了全长1 080 bp的山羊乳腺SCD基因CDS（GenBank登录号：GU947654）并对其进行了生物信息学分析;②奶山羊SCD基因在乳腺、肺和皮下脂肪组织中高表达,而在心脏、瘤胃和卵巢组织中的表达量较低;③成功构建了奶山羊SCD基因的重组腺病毒载体并制备出高滴度的重组病毒液,重组腺病毒感染原代乳腺上皮细胞后,检测结果表明细胞中SCD基因过表达极显著,FASN、H-FABP、LEPR和LXRα等基因表达下调,而PPARγ和LPL基因的表达量显著性增加;④棕榈酸和硬脂酸的含量下降,不饱和脂肪酸含量上升。【结论】SCD基因在奶山羊乳腺中发挥着重要作用,FASN、H-FABP、LEPR、LXRα、PPARγ和LPL基因的表达与其相关,这些基因共同影响乳脂中脂肪酸的组成。