Role of cell proliferation in strobilation of moon jellyfish Aurelia coerulea

The life cycle of the moon jellyfish Aurelia coerulea consists of sessile polyp and free-swimming jellyfish stages. Strobilation is a polyp-to-jellyfish transition comprising sequential segment formation (segmentation), subsequent morphogenesis into ephyrae (young jellyfish), and detachment of the ephyrae. Cell proliferation is involved in metamorphosis in various animals. In the present study, we examined the relationship between cell proliferation and strobilation in A. coerulea. To visualize cell proliferation at various stages of strobilation, 5-bromo-2′-deoxyuridine labeling experiments were conducted, in which cell proliferation was distributed in the segments and prospective regions of the next segment during segmentation. Cell proliferation in segments continues during ephyra morphogenesis. Hydroxyurea, a cell-cycle inhibitor, was administered to investigate cell proliferation in animals at different stages of strobilation. In this study, hydroxyurea interrupted the initiation of strobilation, segmentation, and ephyra morphogenesis, but not ephyra detachment. This suggests that cell proliferation plays a crucial role in generating a new segment and constructing the ephyra body.