Metamorphosis of Hydractinia echinata (Cnidaria) is caspase-dependent.

Apoptotic cell death plays an important role in many developmental pathways in multicellular animals. Here, we show that metamorphosis in the basal invertebrate Hydractinia echinata (Cnidaria) depends on the activity of caspases, the central enzymes in apoptosis. Caspases are activated during metamorphosis and this activity can be measured with caspase-3 specific fluorogenic substrates. In affinity labelling experiments 23/25 kDa bands were obtained, which represented active caspase. Specific inhibition of caspase activity with caspase-3 inhibitors abolished metamorphosis completely, reversibly and in a dose-dependent manner. This suggests that caspase activity is indispensable for metamorphosis in Hydractinia echinata.