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

 

Abstract:  

 

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.