Malate dehydrogenase in subtropical fish belonging to the orders characiformes, siluriformes and perciformes I. Duplicate gene expression and polymorphism

Abstract

1. 1. Electrophoretic analysis of the soluble malate dehydrogenase (sMDH) from 22 subtropical fish belonging to the orders Characiformes, Siluriformes and Perciformes, collected in 10 reservoirs of São Paulo State and in two lakes of Minas Gerais State, Brazil, indicates that at least two sMDH loci, MDH-A ∗ and MDH-B ∗, are active. In addition to this latter locus, in Hoplias malabaricus (Erythrinidae, Characiformes), a MDH-A 1,3 ∗ isoloci is proposed in order to explain the six-banded pattern detected in all the individuals screened. 2. 2. In attempting to explain the multiplicity of compounds detected in 87% of the Geophagus brasiliensis (Cichlidae, Perciformes) specimens analyzed, three hypotheses are proposed: the event of duplication in processing the presence of three loci with a null allele within the MDH-B ∗, and overdominance. 3. 3. In 87% of the species here studied, a bidirectionally divergent pattern of expression of the sMDH loci was observed, in which the least anodal isozyme A 2 predominated in liver, and the most anodal isozyme B 2 predominated in skeletal muscle. In two siluriform species, Pimelodela gracilis and Hypostomus regani, and in one perciform, Tilapia rendalli, a unidirectionally divergent pattern, in which the isozyme A 2 predominated in every tissue analyzed, was observed. 4. 4. Polymorphism in at least one of the sMDH loci was detected in 9% of the species studied here: Leporinus friderici (Characiformes) at the MDH-A ∗ and P. gracilis at both sMDH loci. In L. friderici and Pimelodus maculatus (Siluriformes), rare alleles at the MDH-B ∗ locus were detected. Polymorphism at the mitochondrial locus was detected in Tilapia rendalli.