Submitted to: Animal Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2002
Publication Date: 12/31/2003
Citation: Mitra, A., Foster-Frey, J. A., Wells,K. D., Rexroad,C. E. III, Wells,K. D. and Wall,R. J. (2003) Molecular Characterization lysozyme type II gene in rainbow trout (Oncorhynchus mykiss): Evidence of Gene Duplication. Animal Biotechnology 14:7-12. Interpretive Summary: Fish are becoming an economically important farmed species. However, fish farming often suffers serious financial losses due to outbreak of diseases, particularly bacterial infection. Fish, unlike mammalian species, lack a sophisticated immunological system. Their ability to fight infections mostly depends on innate immunity. Antibacterial proteins like lysozyme appear to play an important role in the defense of fish against bacterial infections. Lysozyme is a bactericidal enzyme that catalyzes the cleavage of linkages in bacterial cell walls, thereby killing bacteria. Lysozyme is ubiquitously found in a wide variety of animals, including fish. In rainbow trout, two types of lysozyme have been isolated. Although type II lysozyme differs from type I by only one amino acid, type II lysozyme has three times more bacterial killing power than type I. Because we want to examine the properties of type II rainbow trout lysozyme further, we isolated the gene. Surprisingly in the process of cloning the gene we discovered that there are actually two genes that encode type II lysozyme, a long form and a short form. The two genes are identical except for about 550 extra nucleotide bases inserted into the long form. The location of the insertion, is in a "spacer region" (intron) and therefore does not alter protein for which the gene codes. The purpose of this manuscript is to report this unexpected observation.
Technical Abstract: Rainbow trout (Oncorhynchus mykiss) has two types of lysozyme. Type II lysozyme differs from type I by only one amino acid, but only type II lysozyme has significant bactericidal activity. Due to this novel antibacterial property, lysozyme II appears to be a candidate gene for potentially enhancing disease resistance in fish as well as livestock species. Using polymerase chain reaction the lysozyme II gene was amplified from genomic DNA isolated from rainbow trout. Two amplified bands of 2041 and 2589 bp were observed. Sequencing of these amplicons revealed that both amplicons were lysozyme gene having the same nucleotide sequence, except the longer fragment has 548 base pairs inserted in intron 2 at nucleotide position 513 and a few point mutations in intron 2. Both versions of trout lysozyme II gene were comprised of four exons and three introns. We also demonstrated that trout lysozyme is most likely coded for by these two different genes, and type I and II variants are the result of allelic variation in those genes.