Shining light on a dark mystery: melanoma in bullhead benthic fish in Lake Memphremagog

Abstract

Malignant melanoma occurs in 30% of the brown bullhead (Ameiurus nebulosus) fish population in Lake Memphremagog, a 40-square-mile lake shared by Vermont (USA) and Quebec (Canada). Despite the broad geographic distribution of brown bullhead, the prevalence and pathology of melanistic growths are unique to this population. Histopathology characteristics of the lesions suggest tumorigenesis is associated with genetic and environmental factors. Preliminary comparative expression analysis confirms that tumor tissue samples have differential gene expression and pathway enrichment consistent with melanoma; however, these sequences lack mutational signatures for UV damage or exposure to a mutagenic agent. We are currently applying a population genomics approach to explore a possible genetic and epigenetic predisposition for tumorigeneses. We assembled and annotated eight high-quality bullhead genomes (built from long nanopore sequencing reads and Illumina short reads) from four geographically distinct and lesion-free populations across Vermont. Using these references, we generated low-coverage genomes using long-read sequencing data from brain tissue of 92 Lake Memphramagog brown bullhead individuals (46 healthy and 46 afflicted) collected from eight sites across the lake. For four afflicted fish, we generated low-coverage genomes for the tumor tissue as well. Here, we will present population genomics results, including population variant analysis, germline vs somatic variation in tumor matched individuals, and methylation differences between populations, as well as between healthy and normal fish.

Biography

Dr. Julie Dragon received her PhD in Plant Biology from the University of Vermont, studying the evolution of an arctic-subarctic section of marsh sedges. For postdoctoral research, she studied the evolution of salt tolerance through hybridization at McGill University, before joining the Department of Microbiology and Molecular Genetics, in 2010, as a bioinformatician, and director of a genomics and bioinformatics core facility. Dr. Dragon focuses her efforts on cataloguing diversity, including reference genome building, variant analysis and metagenomics.