Linkage conservation of homologous esterase loci in fish (Cyprinodontoidei: Poeciliidae)

Differential expression for tissue-specific isozymes in three species of Hypostomus Lacépède, 1803 (Teleostei: Loricariidae)

The expression patterns of 14 enzymatic systems in skeletal muscle, liver and heart tissues of three species of Hypostomus from the Iguaçu River basin (Brazil) were investigated. Although the patterns were similar for the three species, different tissues showed differential expressions, and the data showed that differential tissue expressions of isoperoxidases may be due to preferential combination or association of polypeptide subunits. The detected patterns for SOD isozymes showed that the quaternary structures of these enzymes were in disagreement with the subunit number reported for the majority of other vertebrate groups. Tissue-specific restriction on heterotetramer formation also were described in LDH and MDHP isozymes. Thus, these tissue-specific gene expression character in the species of Hypostomus have the greatest potential to be recognized and applied in systematic studies among species of Hypostomus.

Analysis of an esterase linked to a locus involved in the regulation of the melanoma oncogene and isolation of polymorphic marker sequences in Xiphophorus

Melanoma formation in Xiphophorus hybrids is mediated by a growth factor receptor tyrosine kinase oncogene encoded by the Tu locus. In the wild-type parental fish no tumors occur due to the activity of a locus that regulates the activity of the melanoma oncogene. Molecular identification of this regulatory locus (R) requires a precise physical map of the chromosomal region. Therefore we studied esterase isozymes in Xiphophorus, two of which have been previously reported to be linked to locus R. We confirm that ES1 is a distant marker for R (approx. 30cM), and contrary to earlier studies, we show that this isozyme is present in all species of the genus and at similar activity levels in all organs tested. ES4, which has also been reported to be linked to R, was found to be a misclassification of liver ES1. In an attempt to identify markers that bridge the large distance between ES1 and R, we have generated DNA probes which are highly polymorphic. They will be useful in finding landmarks on a physical map of the R-containing chromosomal region.

Assignment of six enzyme loci to multipoint linkage groups in fishes of the genus Poeciliopsis (Poeciliidae): designation of linkage groups III-V

Three new linkage groups of enzyme loci are described using Poeciliopsis monacha x P. viriosa-derived interspecific backcross hybrids. Comparison to known linkage groups of the confamilial genus Xiphophorus shows homology between Xiphophorus linkage group I and Poeciliopsis linkage group III, Xiphophorus linkage group II and Poeciliopsis linkage group I, and Xiphophorus linkage group IV and Poeciliopsis linkage group IV. Comparison of the gene content of other fish, amphibians, and mammal syntenic groups suggests retention of plesiomorphic vertebrate gene arrangements in at least two poeciliid linkage groups. Expansion of the Poeciliopsis gene map should be of utility in the identification of tumor regulatory genes through demonstration of linkage to biochemical markers.

An analysis of esterase activities from surgeonfish tissues yields evidence of an atypical pseudocholinesterase

1. Esterases from tissues of the surgeonfish (Teleostei, Perciformes, Acanthuridae) are characterized electrophoretically and include several carboxylesterases, an acetylesterase, and an atypical pseudocholinesterase (pseudo-ChE). 2. The pseudo-ChE occurs in several isozymic forms including sialated and asialated slightly-anodal forms found principally in liver, and a larger, asialated asymmetric form that barely penetrates the 10% PAGE gel matrix found together with true AChE in epaxial muscle, brain, and eye. 3. Characterization of these three pseudo-ChE activities suggest that they are decidedly atypical in the intermediacy of their substrate and inhibitor specificities relative to classically-defined AChE and pseudo-ChE activities.

An esterase duplication in Drosophila: differences in expression of duplicate loci within and among related species

An esterase duplication is described in the sibling species pair Drosophila mojavensis and Drosophila arizonensis. We present evidence for two separate structural loci mapping at a distance of less than 0.16 recombination units from each other. Alleles at the two loci have the same substrate specificities and form small amounts of interlocus heterodimers. One locus (Est-5) is functioning throughout the insect's life cycle and appears at high concentrations in the hemolymph and the fat body. Its duplicate (Est-4) functions only during the late larval stage and is concentrated mainly in the carcass. No null alleles at either locus were observed in population surveys. An examination of 12 other species from the repleta group, to which D. mojavensis and D. arizonesis belong, suggests that Est-5 is universally present, but the activity levels of Est-4 vary among species and may be totally absent in some species. Variation in the level of Est-4 activity does not closely follow the phylogenetic relationship.