OXIDATIVE STRESS & INTESTINAL REMODELING DURING AMPHIBIAN METAMORPHOSIS: A BALANCING ACT!
Michelle Christ, and Eileen Gardner
Department of Biology, William Paterson University of New Jersey, Wayne, NJ.
The Anuran intestine undergoes extensive remodeling when the epithelium transforms via larval cell death and adult cell differentiation and proliferation. Involvement of reactive oxygen species (ROS) in tail regression has been reported, but practically nothing is known about the role of ROS in tissue remodeling of the intestine. Our earlier biochemical studies have shown that the cellular environment in the intestine becomes progressively more oxidizing during its remodeling. Since antioxidants are known to safeguard cells from excessive damage from ROS production, our objectives were to evaluate the role of catalase and superoxide dismutase (SOD) during intestinal remodeling in tadpoles of Xenopus laevis (staged according to Nieukoop and Faber, 1967) using western blot analysis and immunohistochemistry (IHS).
To identify the proliferating cells, live tadpoles were injected with BrdU and paraffin sections were stained with anti BrdU. Western blot analyses for catalase and SOD have shown presence of both proteins from stage 58 onwards. IHS at stage 60 (just before remodeling begins) revealed intense staining for catalase in typhlosole (a larval organ) as well as mucosa destined to become adult type, whereas SOD was found to be present only at the boundary of mucosa. Some SOD positive cells in the lumen of the intestine were observed, which could be due to the fact that apoptosis occurs mainly in the cells that line the lumen and these epithelial cells are sloughed in the lumen. At stage 61/62, some cells in mucosa as well as lamina propria stained positive for catalase as well as BrdU but no SOD staining was observed. Positive BrdU staining in mucosa, typhlosole and connective tissue indicated ongoing cell proliferation which may need protection from oxidative stress. Our results support the contention that a) adult intestinal epithelium probably originates from larval epithelial cells and b) presence of catalase and SOD afford protection to these cells from oxidative assault.
Nieuwkoop, P. D. and J. Faber 1967. “Normal Table of Xenopus Laevis.” North Holland Publishing Company. Amsterdam.