Practice question

Hypostome forms dome-shaped apex of Hydra body column containing mouth opening surrounded by tentacle ring. Microsurgical transplantation of isolated hypostome into gastric column of host induces secondary body axis with new head and tentacles, demonstrating organizer activity reminiscent of Spemann-Mangold dorsal lip. Molecularly hypostome secretes Wnt3, maintains high beta-catenin signaling, and expresses BMP antagonists establishing local source that recruits surrounding tissue to head fate. Epidermis contributes differentiated epitheliomuscular cells, mesoglea provides extracellular matrix scaffold, tentacles are terminal structures without organizer ability. Organizer maintained by Wnt3 autocrine loop defines body axis polarity.