student profile: Miss Katherine Brittain


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Thesis work

Thesis title: Evolution and activity of immune genes in Crocodilians

Supervisors: Jaime GONGORA , Sally ISBERG

Thesis abstract:

There are 23 recognised extant species of crocodilians (Crocodylia), which inhabit a large range of tropical, fresh- or saltwater ecosystems around the world. Crocodilians appear to have an effective immune system that allows them to cope with a variety of pathogenic challenges. Even though they live in marshy or stagnant water, individuals that sustain extensive injuries due to inter- and intra-species territory fighting or boat propellers heal rapidly without signs of infection. Crocodilians have been shown to live with a range of opportunistic infections, and yet wild animals seldom display disease symptoms. Also, reptile immune systems are less well studied than their mammalian and avian counterparts, and yet reptiles hold a unique evolutionary position as cold-blooded amniotes. Studying the evolutionary rates of immune system components in crocodilians could contribute to our overall understanding of the development of the immune system. Genetic and peptidome studies of the crocodilian immune system have improved our understanding of the organisation, evolution and diversity of some components of the adaptive immune system (e.g. the Major Histocompatibility Complex) and lead to identification of new host defence peptides. However, there is much yet undiscovered when it comes to components that modulate the functions of the adaptive and innate immune systems in crocodilians, as well as the activity of these components. This project aims to provide a big-picture base knowledge of the components involved in the crocodilian immune system, and how the expression and activity of these genes confers disease resistance. Preliminary analysis of the cytokine family type I interferons (IFN) and their receptors show that crocodilians have no recent IFN gene subtype duplications, contrasting with birds and mammals. Crocodilian subtypes IFNA, IFNB, IFNE group in gene specific phylogenetic clusters and likely evolved independently with no clear orthologous relationship with previously reported IFNA and IFNB or IFNE genes from other species.

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