The lifespan of herbivorous Rana pipiens larvae is ∼3 months, while that of carnivorous Ceratophrys ornata larvae is only about 2 weeks. During metamorphic climax, the larval gut shortens dramatically, especially in R. pipiens, and its luminal epithelium is replaced by adult-type epithelium. To determine when programmed cell death occurs during the metamorphic restructuring of the gut, we prepared cross-sections of the stomach, small intestine, and large intestine from representative larval stages and from juvenile frogs of both species. The sections were incubated with monoclonal antibody against active caspase-3, one of the key enzymes in the apoptotic cascade. We observed apoptosis in some luminal epithelial cells in each of the three regions of the larval gastrointestinal tract of both species. However, apoptotic cells appeared earlier in larval stages of R. pipiens than C. ornata and few were seen in juvenile frogs of either species. The results demonstrate the occurrence of apoptosis in the metamorphic remodeling of the gut of both R. pipiens larvae and C. ornata larvae.
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