Studying Annelida Regeneration in a Novel Model Organism: The Freshwater Aeolosoma viride.

Aeolosoma viride, a globally distributed freshwater annelid, has a semitransparent appearance with 10 to 12 segments, about 2 to 3 mm in length. It is easy to raise and handle in laboratory conditions. Due to its robust regenerative capacity and applicability of various molecular tools including EdU labeling, whole-mount in situ hybridization (WISH), and RNA interference (RNAi), it rises as a promising model for studying whole-body regeneration.

Caspase dependent apoptosis is required for anterior regeneration in Aeolosoma viride and its related gene expressions are regulated by the Wnt signaling pathway.

Although apoptosis has been widely observed during the regenerative process, the mechanisms by which it is regulated and its roles in regeneration remained unclear. In this study, we introduced Aeolosoma viride, a fresh water annelid with an extraordinary regenerative ability as our model organism to study the functions and regulations of apoptotic caspases. Here we showed that major events of apoptosis were detected near the wounded area and showed spatial correlation with the expression patterns of caspase gene namely Avi-caspase X and two apoptosis regulators namely Avi-Bax and Avi-Bcl-xL. Next, we investigated how Avi-caspase X gene expression and apoptosis influence regeneration following head amputation. RNA interference of Avi-caspase X reduced the amounts of apoptotic cells, as well as the percentage of successful regeneration, suggesting a critical role for apoptosis in anterior regeneration of A. viride. In addition, we also discovered that the expression of apoptotic caspases was regulated by the canonical Wnt signaling pathway. Together, our study showed that caspase dependent apoptosis was critical to the anterior regeneration of A. viride, and could be regulated by the canonical Wnt signaling pathway.