Selective expression of the mitochondrial genes from Ascaris suum

我们一直在研究猪蛔虫对氧分压适应的分子机制。成体猪链霉菌居住在宿主小肠，那里的氧气张力较低，并利用独特的厌氧线粒体呼吸链来适应其微氧栖息地。在这个厌氧呼吸链中，NADH的还原当量通过罗丹酚(NADH-富马酸还原酶)转移到富马酸。与成虫线虫相比，幼虫发育需要氧气，幼虫线粒体的呼吸链与哺乳动物宿主的呼吸链相似。需要强调的是，与哺乳动物的酶不同，成虫的复合体II的功能是相反的，作为富马酸核酸酶(FRD)，而不是琥珀酸脱氢酶(SDH)。在本研究中，我们第一个令人兴奋的结果是在猪链霉菌线粒体中发现了阶段特异性的复合体II亚型。幼虫复合体II不同于成虫酶a…更多的ND更类似于富马酸还原酶活性较低的有氧哺乳动物宿主酶。对黄素蛋白亚基(FP)的序列分析表明，猪链霉菌成虫复合体II是由线虫等自由生活线虫的复合体II进化而来的。猪链霉菌成虫复合体II的富马酸还原酶活性可能是在其向寄生生活型转变的过程中适应微氧生境而获得的。通过比较研究和对丝虫复合体II的cDNA序列分析，证实了这一观点。除FP外，还克隆了成体复合体II小亚基(CybS)的基因。最近，我们在克隆幼虫线粒体中表达的主要细胞色素c(类型1细胞色素c)的过程中发现了成虫特有的细胞色素c(类型2细胞色素c)亚型。因此，我们通过线粒体呼吸链的动态变化，揭示了猪乳菇在生活周期中在不同环境中生存的策略。较少

We have been studying about the molecular mechanism of adaptaion to oxygen tensions by using parasitic nematode, Ascaris suum. The adult A.suum resides in the host small intestine, Where oxygen tensions are low, and has exploited a unique anaerobic mitochondrial respiratory chain as an adaptation to its microaerobic habitat. In this anaerobic respiratory chain, the reducing equivalents from NADH are transferred to fumaarate via rhodoquinone (NADH-fumarate reductase). In contrast to the adult nematode, oxygen is required for larval development, and the respiratory chain of larval mitochondria is similar to that of mammalian host. It should be stressed that unlike the mammalian enzyme, complex II of adult A.suum functions in the reverse direction, as a fumarate reuctase (FRD) rather than as a succinate dehydrogenase (SDH).In this study, our first exciting result is the discovery of stage-specific isoforms of complex II in A.suum mitochondria. Larval complex II differs from adult enzyme a … More nd is more similar to aerobic mammalian host enzyme with low fumarate reductase activity. Sequence analysis of flavoprotein subunits (Fp) suggests that A.suum adult complex II evolved from complex II of free-living nematodes, such as Caenorhabditis elegans. The fumarate reductase activity of the A.suum adult complex II probably was acquired during its adaptation to microaerobic habitats during the transition to a parasitic life style. Comparative study and cDNA sequence of complex II from Dirofilaria immitis confirms this idea. In addition to Fp, cDNA for small subunit of adult complex II (cybS) was cloned and sequenced. This is the first sequcnce information on the mitochondrial cybS.Recently, we found adult-specific isoform of cytochrome c (type-2 cytochrome c) during the cDNA cloning of major cytochrome c (type-1 cytochrome c) expressed in larval mitochondria. Thus, we showed the strategy of A.suum to survive in the various environment during their life cycle by the dynamic change of mitochondrial respiratory chain. Less