Insights on the intracellular trafficking of calcifying medium in a reef-building coral

Biomineralization is the process by which corals build their exoskeletons, and ultimately the reef ecosystem framework. The current model of biomineralization in these animals involves the endocytosis of calcifying medium by the calcifying cells lining the exoskeleton, followed by the intracellular formation of amorphous calcium carbonate precursors. However, the intracellular trafficking pathways inside these cells are poorly described. In this study, we investigated the intracellular trafficking of calcifying medium at the growing edge of laterally extending Stylophora pistillata colonies. Using a combination of fluorescent probes and immunofluorescence, along with confocal microscopy in living and fixed samples, we observed that a portion of the endocytosed calcifying medium is directed towards the Rab11-dependent endosomal recycling system, and we suggest that this pathway can be involved in the process of biomineral formation.