Cardiac regeneration in Xenopus tropicalis and Xenopus laevis: discrepancies and problems

Two studies have recently focused on adult heart regeneration in Xenopus. While we reported on cardiac myogenic regeneration in Xenopus tropicalis after injury, Marshall and colleagues found no regeneration in an injured heart in Xenopus laevis. Here, we would like to join the discussion initiated by Marshall et al. who debated the methods and species differences in both studies. We agree with their view that the species difference in cardiac regenerative capacity could lead to different results in both of these studies. Moreover, we suggest that the age of the animals used in these studies could lead to differences in regeneration. A 5-year old X. laevis is much more advanced in age than a 1-year old X. tropicalis. The other reason for the discrepancies could be the size of the clot. Due to different resection protocols, the clot formed after the endoscopic resection performed by Marshall et al. was much larger than that after a conventional resection, as used in our study. Furthermore, the difference in the site of injury could influence the healing and regeneration differences. The influence of the organismal age, techniques used to induce injury and site of injury on regeneration need to be examined in detail to assess the regenerative potential of the amphibian heart.