MicroRNA, mRNA and protein responses to dehydration in skeletal muscle of the African-clawed frog, Xenopus laevis

During the dry season in southern Africa, the predominantly aquatic African-clawed frog (Xenopus laevis) burrows into the wet mud of ponds and marshes. As drying continues frogs undergo dehydration, often enduring the loss of over 30% of body water. The present study examines the role of miRNA action in mediating biochemical changes that support X. laevis endurance of dehydration. Three conditions were analyzed: control, medium dehydration (15% total body water lost) and high dehydration (30% total body water lost) and relative changes in skeletal muscle miRNA, mRNA and protein expression were measured. The results showed statistically significant increases of 1.8-2.4 fold in the expression, relative to controls, of two proteins involved in miRNA biogenesis, Dicer and Drosha, as well as reduced serine phosphorylation of a third protein, p-Ago2 (Ser 387). Levels of two specific miRNAs were also elevated during medium dehydration by 1.9 and 2.5 fold for miR-181a3p and miR-210-5p, respectively. Gene transcript levels of selected muscle proteins were also altered: a 10-15 fold increase in mstn2 (myostatin 2), a 5-6 fold increase in mybpc3.S (myosin binding protein cardiac 3) and a 2.3fold rise in tnnc2 (troponin C2) but oppositely a significant decrease in expression of myod1 (myoblast determination protein 1). These findings indicate an increase in miRNA biogenesis, muscle contractile proteins and hypoxia stress tolerance with an opposite decrease in muscle growth and differentiation under dehydrating conditions that could all contribute to X. laevis survival of extreme dehydration.