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Glutamine synthetase as a biological marker for fish phylogenetics : some new insights Laberge Macdonald, Tammy

Abstract

Glutamine synthetase is a key enzyme for nitrogen metabolism. It occurs in all organisms and is one of the oldest functioning genes. Many vertebrates have only one functional copy of this gene, while many plants have been shown to be multicopy for this gene. Pseudogenes for glutamine synthetase have also been reported in mammals. Until recently only a single copy of glutamine synthetase had been described in fish. However, six copies of this gene are expressed in rainbow trout Oncorhynchus myklss and two copies of this gene are expressed in the gulf toadfish Opsanus beta. We investigated a variety of intertidal fishes from British Columbia, Canada using PCR amplification of genomic DNA product and reverse transcriptase PCR to explore the diversity of glutamine synthetase in fish. We recovered two isoforms of glutamine synthetase in fourteen out of twenty-one fish. We describe the partial sequences for the two copies of this gene that differed in nucleotide composition by 8 to 22 percent. Phylogenetic analysis was performed using the different glutamine synthetase isoforms to generate trees for intertidal fishes collected in this study. Fish from the following orders were represented in this study: Myxiniformes, Lepisosteiformes, Salmoniformes, Gasterosteiformes, Syngnathiformes, Scorpaeniformes, Perciformes and Pleuronectiformes. Most species adhered to the traditional taxonomic classification although some representative fish did not.

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