Abstract

In terrestrial mammals, the tear film plays an essential role in maintaining the health of the ocular surface as it protects against toxic challenges in the external environment, thereby preserving visual acuity. These protective functions are critically dependent upon the integrity of the tear film structure, which is comprised of three layers: an underlying mucin foundation, a protein-rich aqueous component, and an overlying lipid layer. In a previous study, we determined that the tears of marine mammals do contain proteins, but that the tear film, examined using interferometry, appears to lack the lipid layer found in terrestrial mammals. This finding is quite significant in that it indicates that in sea mammals an alternative component, in lieu of lipid, promotes the stability of the tear film. This led us to hypothesize that, in the absence of a lipid layer, a mucin foundation, similar to that found in terrestrial mammals, may be critical to the integrity of the tear film of marine mammals.

Lectin binding to high molecular weight proteins is highly indicative of the presence of mucins. The purpose of this study was to determine whether sea mammals express tear glycoproteins similar to those found in terrestrial mammals. In order to assess whether mucins were present in marine mammal tears, samples from bottlenose dolphins were analyzed for lectin binding. Tear samples collected from marine mammals were subjected to electrophoresis on SDS-agarose gels to separate out large proteins, which were then transferred by Western blotting onto nitrocellulose membranes and analyzed for the binding of a variety of lectins, including peanut agglutinin (PNA), wheat germ agglutinin (WGA), Maackia amurensis II (MAL II), and Sambucus nigra (SNA) to probe for the presence of mucins. Of the four lectins tested thus far, three did bind to high molecular weight proteins isolated from the tears of bottlenose dolphins. This finding strongly suggests that large mucins are present in the tears and may play a critical role in the protection of the surface of the eyes of these marine mammals.

Acknowledgements

We thank Dr. Sam Ridgway (U.S. Navy Marine Mammal Program, San Diego, CA) for generously providing ocular secretion samples from bottlenose dolphins. We also thank Pablo Argueso and Sandra Spurr-Michaud (S.ER.I. & H.M.S., Boston, MA) for technical advice. This work was supported by grants from Arey's Pond Boat Yard, Inc. and N.I.H. [EY05612].