Mannose binding lectin (MBL) copy number polymorphism in Zebrafish (D. rerio) and identification of haplotypes resistant to L. anguillarum
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We describe a novel extension of the Genomic Matching Technique (GMT) that defines haplotypes of the mannose binding lectin (MBL) region in Zebrafish (D. rerio). Four ancestral haplotypes have been identified to date, with at least one of these demonstrating a significant increase in resistance to L. anguillarum. MBL activates the lectin pathway of the complement system and stimulates the development of the complement cascade and the Membrane Attack Complex. Polymorphisms in humans have been associated with increased susceptibility and severity to a number of pathogenic organisms. As teleosts have a relatively immature acquired immune system, polymorphisms within MBL and other innate defence genes are likely to be critical in defining their susceptibility/resistance to various pathogenic organisms. We report multiple copies of MBL-like genes in D. rerio, with up to three copies tightly linked within a cluster spanning ∼15 kb on chromosome 2. Genomic analysis suggests that duplication, retroviral insertion and possibly gene mutation and/or deletion have been key factors in the evolution of this cluster. Molecular analysis has revealed extensive polymorphism, including at least five distinct amplicons and haplospecific gene copy number variation. This study demonstrates polymorphism within a critical component of the teleost innate immune system. The polymorphisms and the haplotypes encoding the unique variants are likely to be informative in defining susceptibility/resistance to infectious agents commonly encountered within aquatic environments. Future investigations will define other important haplotypes and transfer the knowledge to other finfish species, thereby enabling selection of broodstock for the aquaculture industry.
KeywordsZebrafish Lectin pathway MBL Ancestral haplotypes Genomic matching technique L. anguillarum
The authors thank Nicki Buller and Brian Jones of the Animal Health Laboratories (Department of Agriculture and Food, Western Australia) for supplying bacterial pathogens and advice on pathogen culturing. This study is supported by Genetic Technologies Ltd., Fitzroy, Victoria, 3065, Australia and the C.Y. O’Connor ERADE Village Foundation. Collectively, the authors associated with the C.Y. O’Connor ERADE Village Foundation have an interest in Genetic Technologies.
The project was vetted then approved by the Murdoch University Animal Ethics Committee. All fish used were maintained and treated humanely and euthanased at the completion of work.
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