中国科学院昆明动物研究所机构知识库

不饱和脂肪酸（Unsaturated Fatty Acids, UFAs）作为一种基本的营养成分，对于维持生命体的正常生理功能具有非常重要的作用。不饱和脂肪酸可以参与调控细胞膜的流动性以及韧性，此外其还可以作为前体来合成一些重要的信号分子如前列腺素、白细胞三烯等。其次，不饱和脂肪酸对于调控生长发育，能量代谢以及应激反应也具有非常重要的作用。 不饱和脂肪酸包括单不饱和脂肪酸(Monounsaturated Fatty Acids, MUFAs)以及多不饱和脂肪酸(Polyunsaturated Fatty Acids, PUFAs)，单不饱和脂肪酸的生物合成是通过硬质酰辅酶A去饱和酶（Stearoyl-CoA desaturase，SCD）在饱和脂肪酸的碳骨架上的特定位置引入一个不饱和双键形成的，而单不饱和脂肪酸再经由其它特异性的去饱和酶在特定位置继续引入一个或多个双键进而形成多不饱和脂肪酸。秀丽线虫拥有三个编码SCD的基因，分别编码FAT-5、FAT-6和FAT-7，其中FAT-5主要催化C16：0转变为C16：1(n-7)，而FAT-6和FAT-7主要催化C18：0转变为C18：1(n-9)。此前已有文献报道去饱和作用需要去饱和酶、细胞色素b5还原酶以及细胞色素b5协同发挥作用，然而这个多酶系统如何发挥功能还不是很清楚。模式生物秀丽隐杆线虫生长周期短，具有完整的不饱和脂肪酸合成体系，并且此合成体系与哺乳动物高度保守。因此我们选用秀丽隐杆线虫来对去饱和酶作用体系进行研究。 在本研究中，我们通过使用人和小鼠编码细胞色素b5基因的氨基酸序列进行比对预测确定cytb-5.1和cytb-5.2可能在线虫中编码细胞色素b5蛋白。我们利用气象色谱分别检测了cytb-5.1和cytb-5.2干扰株线虫以及突变株线虫的脂肪酸成分，其中cytb-5.1干扰株线虫以及突变株线虫的C18：0脂肪酸均出现了明显的上调，而C18：1(n-9)则均出现了明显的下降，向线虫的食物中添加C18：1(n-9)和C18：2(n-6)发现C18：1(n-9)和C18：2(n-6)以及下游的不饱和脂肪酸的含量获得了一定程度的恢复，最终确定CYTB-5.1特异性的调控FAT-6和FAT-7的活性。然而cytb-5.2干扰株线虫仅在F1代出现了C16:0和C18：0的升高，但是其突变株cytb-5.2（VC20530）却表现出明显的C16：0升高，C16:1（n-7）含量降低，在对cytb-5.2（VC20530）进行C16：1(n-7)，C18：1(n-9)添加实验以后确定CYTB-5.2特异性的调控FAT-5的活性。

Unsaturated fatty acids (UFAs)，as a basic nutritional ingredient, play an important role in maintaining normal physiological functions in living organism.Unsaturated fatty acids not only can regulate the fluidity and flexibility of the cell membrane, it can also as the precursor to synthesize some important signal molecules like prostaglandin and leukotrienes. In addition, it is also important to regulate the growth and development, energy metabolism and stress response. Unsaturated fatty acids are comprise of monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs), The biosynthesis of UFAs starts from the introduction of the first double bond to the carbon skeleton by Stearoyl-CoA desaturase (SCD) that converts saturated fatty acids (SFAs) to monounsaturated fatty acids (MUFAs), then other specific desaturases continue to introduce one or more double bond to the carbon skeleton of MUFAs to synthesize the PUFAs. C. elegans possess three SCD genes that encode FAT-5, FAT-6 and FAT-7 respectively, among which the FAT-5 catalyzes the conversion of C16:0 to C16:1(n-7), and FAT-6 and FAT-7 catalyze the conversion of C18:0 to C18:1(n-9).This desaturation has been considered as an aerobic process requiring cytochrome b5 reductase, cytochrome b5 and SCD. However, this enzyme system has not been well characterized so far. The model organism C. elegans has a short growth cycle, and has a conservative synthetic system of UFAs. Therefore, we choose C. elegans as a model organism to research the system of desaturation. Here, we use the amino acid sequences of mice (mCYB5A and mCYB5B) as well as human (hCYB5A and hCYB5B) cytochrome b5 to search for orthologues in C. elegans. BLAST results showed that C31E10.7 (CYTB-5.1) and W02D3.1 (CYTB-5.2) might be cytochrome b5. Then we detect the fatty acid profiles of cytb-5.1 and cytb-5.2 RNAi worms and mutant worms respectively by GC. RNAi knockdown or mutant of cytb-5.1 led to increased level of saturated fatty acid C18:0,but decreased levels of C18:1(n-9) in model organism C. elegans. Dietary supplementation with C18:1(n-9) and C18:2(n-6) demonstrated that CYTB-5.1 affect the activity of FAT-6 and FAT-7 desaturases exclusively. However, the cytb-5.2 RNAi worms only show an increased level of C16:0 and C18:0, but the mutant cytb-5.2（VC20530）show an increased level of C16:0, but decreased levels of C16:1(n-7). Dietary supplementation with C16:1(n-7) and C18:1(n-9) demonstrated that CYTB-5.2 affect the activity of FAT-5 desaturase.