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Albinism and the Conservation of Pigment cells in Cave Animals

The loss of body pigmentation has evolved independently in multiple animal taxa that have successfully colonized subterranean habitats. By using the melanogenic substrate assay, we have gained two insights into the mechanisms underlying albinism in a diverse variety of cave-dwelling animals. The first insight is that pigment cells capable of using L-DOPA to synthesize melanin are conserved in a variety of cave animals in spite of the absence of melanin synthesis, suggesting that these cells may have roles other than pigment formation. Studies of wound healing in arthropods have provided a clue for one of these roles: melanization of wound sites is a widespread feature that is conserved even in cave-dwelling arthropod species that have lost body melanin body pigmentation. Furthermore, we have found that melanophores or colorless cells capable of melanin synthesis congregate near wound sites in Astyanax embryos. These studies suggest that pigment cells may be important in innate immunity, which would explain their conservation during troglomorphic evolution. The second insight is that melanin synthesis is blocked at its first step in a wide variety of cave-dwelling animals. This first step could be a frequent target of disruption because: i) it is energetically most efficient to block melanin synthesis at its beginning, ii) the disruption of other steps in the pathway would generate reactive oxygen species and other toxic intermediaries, and/or iii) L-tyrosine, the initial substrate can be used to enhance other metabolic pathways, such as the catecholamine synthesis pathway. We are testing these possibilities and have demonstrated a link between the catecholamine and melanin synthesis pathways via oca2 loss of expression in Astyanax. Preliminary evidence also suggests that catecholamines are increased in albino cave invertebrates.

cave-dwelling animals, albinism, melanophores, catecholamines

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