Helen Alyx Holden, M.Sc. Biology, 2011

Anuran adaptations to climatic stress: Immune responses and the SMAD family in the wood frog, Rana sylvatica, and the African clawed frog, Xenopus laevis




The wood frog, Rana sylvatica, survives freezing over winter. The African clawed frog, Xenopus laevis, withstands substantial dehydration seasonally. The effects of environment on these frogs‟ immunity were investigated with a focus on antimicrobial peptides. Expression of brevinin-1SY was analyzed during freezing, dehydration, anoxia, and development in R. sylvatica. Brevinin-1SY responded differently to each stress, suggesting environmentally regulated expression. Upregulation of hepcidin mRNA was demonstrated during dehydration in X. laevis liver, as were hepcidin agonists, STAT 3 and cMYC. Alternatively, hepcidin antagonizing TGF-β-mediated SMADs were downregulated and the BMP-mediated SMADs, promoters of hepcidin expression, did not change. Molecular controls of X. laevis skeletal muscle growth were also explored during dehydration. Myostatin, a muscle growth antagonizer, was downregulated during dehydration, whereas cMYC, a muscle growth agonizer, and GLUT 4, a glucose transporter, were upregulated; differential control of SMADs was documented. The data suggest that, during estivation, muscle growth signals are promoted.