Interaction of the retinoic acid signaling pathway with spicule formation in the marine sponge Suberites domuncula through activation of bone morphogenetic protein-1

► Sponges as a model system for molecular skeleton formation. ► Sponges as a model system for studies on the morphogens retinol/retinoic acid. ► Shaping the morphology of siliceous spicules. ► Key enzymes involved in the metabolism of retinol in sponges have been identified. ► Data indicate that retinoids regulate the appositional growth of the siliceous spicules.