Evolutionary Fates of Hemoglobin and Heme Scavengers in White-blooded Antarctic Icefishes

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This work will broaden our knowledge and insights into genetic trait loss or change accompanying species evolution in general as well as within the uniquely isolated and frigid Southern Ocean. The system of oxygen-carrying and related proteins being studied is very important to human health and the two proteins being specifically studied in this work (haptoglobin and hemopexin) have crucial roles in preventing excess iron loading in the kidneys. As such, the project has the potential to contribute novel insights that could be valuable to medical science. The project will also further the NSF goals of training new generations of scientists and of making scientific discoveries available to the general public. The lead principal investigator on the project is an early career scientist whose career development will be enhanced by this project. It will also support the training of several undergraduate students in molecular biology, protein biochemistry, and appreciation of the unique Antarctic fish fauna and environment. The project will contribute to a content-rich web site that will bring to the public the history of biological discoveries and sciences on fishes of the Southern Ocean and through this project the investigators will contribute to an annual polar event at a children's science museum. The Antarctic icefishes have thrived despite the striking evolutionary loss of the normally indispensable respiratory protein hemoglobin in all species and myoglobin in some. Studies over the past decades have predominately focused on the mechanisms behind hemoprotein losses and the resulting compensatory adaptations in these fish, while evolutionary impact of such losses on the supporting protein genes and functions has remained unaddressed. This project investigates the evolutionary fate of two important partner proteins, the hemoglobin scavenger haptoglobin and the heme scavenger hemopexin (heme groups are the iron-containing functional group of proteins such as hemoglobin and myoglobin). With the permanent hemoglobin-null state in Antarctic icefishes, and particularly in dual hemoglobin- and myoglobin-null species, the preservation of a functional haptoglobin would seem unessential and the role of hemopexin likely diminished. This project seeks to resolve whether co-evolutionary loss or reduction of these supporting proteins occurred with the extinction of the hemoglobin trait in the icefishes, and the molecular mechanisms underlying such changes. The investigators envisage the cold and oxygen rich marine environment as the start of a cascade of relaxation of selection pressures. Initially this would have obviated the need for maintaining functional oxygen carrying proteins, ultimately leading to their permanent loss. These events in turn would have relaxed the maintenance of the network of supporting systems, leading to additional trait loss or change.