In cap stage, the cell in the centre of enamel organ secrete glycosaminoglycans, which are:

The cells in the centre of enamel organ synthesize and secrete glycosaminoglycans into the extracellular compartment between the epithelial cells. Glycosaminoglycans are hydrophilic and so pull water into the enamel organ. The increasing amount of fluid increases the volume of the compartment of the enamel organ, and the central cells are forced apart. Because they retain connections with each other through desmosomal contacts, they become star-shaped. The center of the enamel organ thus is termed the stellate reticulum.