Selective expression of the mitochondrial genes from Ascaris suum

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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