Characterization of a microsomal retinol dehydrogenase gene from amphioxus: retinoid metabolism before vertebrates

Amphioxus, a member of the subphylum Cephalochordata, is thought to be the closest living relative to vertebrates. Although these animals have a verte brate-like response to retinoic acid, the pathway of retinoid metabolism re mains unknown. Two different enzyme systems - the short chain dehydrogenase /reductases and the cytosolic medium-chain alcohol dehydrogenases (ADHs) - have been postulated in vertebrates. Nevertheless, recent data show that th e vertebrate-ADH1 and ADH4 retinol-active forms originated after the diverg ence of cephalochordates and vertebrates. Moreover, no data has been gather ed in support of medium-chain retinol active forms in amphioxus. Then, if t he cytosolic ADH system is absent and these animals use retinol, the micros omal retinol dehydrogenases could be involved in retinol oxidation. We have identified the genomic region and cDNA of an amphioxus Rdh gene as a preli minary step for functional characterization. Besides, phylogenetic analysis supports the ancestral position of amphioxus Rdh in relation to the verteb rate forms. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.