A field-study of inducible molecular defenses, ultraviolet radiation, and melanomagenesis in natural Xiphophorus hybrids

Ultraviolet radiation-the primary natural pollutant affecting melanomagenesis-may represent a widespread ecological stressor for many fishes, and yet the relationship between UV-exposure and stress has not been investigated in natural fish populations. Recent lab-based studies have sought to characterize the relationship between tumorigenesis and the induction of molecular defenses, such as heat shock proteins. Here we show that ultraviolet radiation and heat shock protein gene expression explain a significant amount of the variation in hyper-melanization-the phenotypic precursor to melanoma-in wild hybrids of Xiphophorus, laboratory models in cancer research. Our results suggest exposure to UV radiation causes stress which induces molecular defense mechanisms, which in turn may facilitate tumorigenesis in natural fish populations. Studies of laboratory-based model organisms in natural settings, like this one, may provide important insights into ecological and evolutionary relationships obscured in controlled laboratory environments. We hope that ours is only the first of many studies to investigate the such relationships between environmental stress, stress-induced molecular defenses, and cancer in fishes. © Springer Science + Business Media B.V. 2009