Two Zebrafish Alcohol Dehydrogenases Share Common Ancestry with Mammalian Class I, II, IV, and V Alcohol Dehydrogenase Genes but Have Distinct Functional Characteristics

Abstract

Ethanol is teratogenic to many vertebrates. We are utilizing zebrafish as a model system to determine whether there is an association between ethanol metabolism and ethanol-mediated developmental toxicity. Here we report the isolation and characterization of two cDNAs encoding zebrafish alcohol dehydrogenases (ADHs). Phylogenetic analysis of these zebrafish ADHs indicates that they share a common ancestor with mammalian class I, II, IV, and V ADHs. The genes encoding these zebrafish ADHs have been named Adh8a and Adh8b by the nomenclature committee. Both genes were genetically mapped to chromosome 13. The 1450-bp Adh8a is 82, 73, 72, and 72% similar at the amino acid level to the Baltic cod ADH8 (previously named ADH1), the human ADH1B2, the mouse ADH1, and the rat ADH1, respectively. Also, the 1484-bp Adh8b is 77, 68, 67, and 66% similar at the amino acid level to the Baltic cod ADH8, the human ADH1B2, the mouse ADH1, and the rat ADH1, respectively. ADH8A and ADH8B share 86% amino acid similarity. To characterize the functional properties of ADH8A and ADH8B, recombinant proteins were purified from SF-9 insect cells. Kinetic studies demonstrate that ADH8A metabolizes ethanol, with a V max of 13.4 nmol/min/mg protein, whereas ADH8B does not metabolize ethanol. The ADH8A K m for ethanol as a substrate is 0.7 mM. 4-Methyl pyrazole, a classical competitive inhibitor of class I ADH, failed to inhibit ADH8A. ADH8B has the capacity to efficiently biotransform longer chain primary alcohols (>5 carbons) and S-hydroxymethlyglutathione, whereas ADH8A does not efficiently metabolize these substrates. Finally, mRNA expression studies indicate that both ADH8A and ADH8B mRNA are expressed during early development and in the adult brain, fin, gill, heart, kidney, muscle, and liver. Together these results indicate that class Ilike ADH is conserved in zebrafish, albeit with mixed functional properties.Fetal alcohol syndrome in children born to women who consumed alcohol during pregnancy was first described by Jones and colleagues in 1973 (1). Fetal alcohol syndrome is characterized by a delay in development, cardiac abnormalities (1), central nervous abnormalities, abnormal craniofacial features, and intellectual delays (1, 2). The teratogenic properties of ethanol have been firmly established; however, the underlying mechanism(s) of toxicity remain unclear. Two molecular mechanisms have been proposed: direct ethanol effects and the indirect effects associated with acetaldehyde formation and oxidative stress (3). The ability of ethanol to cause developmental anomalies has been demonstrated in mice, rats, Drosophila melanogaster, and chickens (4 -7). Zebrafish are well suited for genetic studies (reviewed in Ref. 8). Zebrafish embryos exposed to ethanol display craniofacial abnormalities, cardiac and structural malformations, and development delay (9 -11). Visual function was affected in embryos exposed to 1.5% ethanol during development (12). Recent studies indicate that three adult strains of zebrafish display different behavior...

Fetal alcohol exposure impairs hedgehog cholesterol modification and signaling

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