Spicule transport during skeletal organization in Demosponges
Sponges produce siliceous skeletal elements, termed spicules, which are assembled to form their skeleton. Intriguingly, these spicules do not form at their final position. Instead, they develop inside the organism and are actively transported to their destination.
This project seeks to identify the biophysical mechanisms that enable this active transport and the underlying principles of self-organization. Specifically, we study the hatching of gemmules during asexual reproduction in freshwater demosponges, when totipotent cells initiate cell differentiation and spiculogenesis. Spicule-forming cells exhibit highly motile collective behavior, transporting nascent spicules through the developing tissue. By combining confocal fluorescence microscopy of gemmules stained with a Si-specific fluorescence marker, X-ray-based micro-tomography of mature sponges, and state-of-the-art image segmentation and analysis, we quantify cell and spicule dynamics in 3D. Together with data-driven modeling, we infer transport rules and biophysical mechanisms that ensure the spatial organization of spicules. These studies provide new insight into skeletal assembly in Demospongiae and may establish sponge morphogenesis as a striking example of active matter, in which self-organized collective motility contributes to tissue organization.