The African lungfish mucus cocoon is a living tissue with antimicrobial functions

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The transition of vertebrates from aquatic to terrestrial environments was one of the most remarkable steps in evolutionary history. The environmental conditions of land ecosystems imposed new physiological challenges to vertebrates including desiccation stress, UV damage and novel pathogens. Lungfish (Dipnoi), the closest ancestors of all tetrapods, aestivate forming a cocoon that covers their entire body and protects them against external aggressions. This cocoon has been viewed thus far as an inert layer made of glycoproteins. The researchers propose that this cocoon is in fact a living tissue that protects the lungfish against pathogen invasion for long periods of time. The goal of this project is to determine the structure and function of lungfish cocoons from both laboratory animals and animals caught from the wild in Tanzania. Another goal is to identify how the cocoon protects the lungfish from pathogens during aestivation and if specific immune mechanisms are involved. The societal outcomes of this proposal are to establish the US as a global leader in STEM research and education and to level the gender gap in STEM both in the US and Tanzania. This will be achieved by cross-training summer programs targeted to increase women and minorities representation in STEM.This project’s intellectual merit is to investigate novel immunological structures and mechanisms used by vertebrates to adapt to environmental stress. Lungfishes are a good model to answer this question since they can adapt to terrestrial environments under unfavorable conditions. The lungfish cocoon, thought to be an inert mucus layer, has been largely understudied. Preliminary studies indicate that this cocoon may be a living tissue with unique immunological capabilities. Specifically, the researchers hypothesize that the cocoon acts as a living, microbe-trapping structure that utilizes neutrophil extracellular traps (NETs) to halt pathogen invasion during the aestivating months when the lungfish are immobile. A variety of histological, immunological, molecular and sequencing approaches will be used to determine the structure and function of the lungfish cocoon. The immune cells and molecules involved in protection against pathogens in the cocoon will be identified. Laboratory-based experiments will be coupled to field collections. This research has the potential for advances in the fields of evolutionary biology and immunology by characterizing immunological mechanisms that allow lungfish to adapt to dessication stress, a key trait that would allow adaption to terrestrial environments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.