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R. Kelleher Davis, D. A. Sullivan, P. Argueso; Characteristics of Mucin-Type O-Glycans in Marine Mammal Tears. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4163.
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© ARVO (1962-2015); The Authors (2016-present)
Marine mammals experience varying degrees of desiccation stress of the ocular surface depending on the phylogeny. For example, pinnipeds spend considerable time on land and ice, but cetaceans are almost entirely aquatic. We hypothesize that mucin-type glycoproteins and their carbohydrates (O-glycans) are protective components of the marine mammal tear film and that different species have unique compositions depending on the degree of exposure to air.
Tear secretions from cetaceans (Atlantic bottlenose dolphins), pinnipeds (California sea lions), and humans, were collected via capillary suction or absorption onto cellulose sponges, and analyzed by bicinchoninic acid assay to determine protein concentration. Tear samples normalized for protein content were electrophoresed on 1% SDS-agarose gels, and proteins were transferred to nitrocellulose membranes by vacuum blotting. To detect mucin-type O-glycans, membranes were probed for the T-antigen carbohydrate using Arachis hypogaea agglutinin (PNA), followed by chemiluminiscence detection.
The tear protein concentration of cetaceans (.05-.60 mg/ml, n=6) was lower than that of pinnipeds (.20-1.2 mg/ml, n=3), and both were lower than reported values for human tears (4.21-9.40 mg/ml; Invest Ophthalmol Vis Sci 32:2290-2301,1991). PNA binding to proteins of high molecular weight (>250 kDa), consistent with the molecular weight of mucins, was detected in the tear fluid of marine mammals and humans. The size distribution of the PNA-positive bands was different for each species analyzed, with cetaceans having the largest molecular weights and humans the smallest.
These results indicate that, similar to humans, mucin-type O-glycans are present in the tears of cetaceans and pinnipeds. These findings support our hypothesis that levels of exposure to air or water correlate with the different biochemical properties of mucin glycoproteins in the tear film.Acknowledgments:We thank Aquarium of Niagara, Niagara Falls, NY and Dolphin Quest Oahu, Oahu, HI for contributions of marine mammal tears.
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