Allogenic grafting induces PI3K-mediated tissue overgrowth in hydrozoan jellyfish Cladonema radiatum medusae

Allorecognition, which is the ability of an organism to discriminate between self and non-self, protects multicellular animals from somatic cell/germline parasitism. We reported and characterised allorecognition in the stolons of colonies of the hydrozoan jellyfish Cladonema radiatum (C. radiatum) in our previous publication. C. radiatum has a free-swimming medusa form besides the sessile colonial form. In this study, we investigated the allorecognition responses in the medusa form of C. radiatum. By using grafting experiments, we observed that while C. radiatum medusae show tolerance to both isogenic and allogenic chimerism, allogenic grafting induces the formation of a form of circular scars—we refer to as “ring-shaped scars”—around the grafts on the host umbrella. Within the scars, overgrowth of tissues occurs with additional gastrovascular canal development. By pharmaceutical experiments, we found that tissue overgrowth is dependent on phosphoinositide 3-kinase (PI3K) and vascular endothelial growth factor (VEGF), showing a resemblance to mammalian neoplasia.