Fig. 2.

Graphical Illustration of ameloblasts showing proteins critical for the secretory stage. CLDN1, CLDN10, CLDN16, and CLDN19 encode tight junction proteins restricting entry of intercellular ions and molecules into the enamel space and also function in cell motility. GJA1 encodes a gap junction protein important for intercellular communication with adjacent ameloblasts. FAM20A and FAM20C encode components of the Golgi casein kinase complex that phosphorylates secreted enamel proteins. FAM83H encodes a cytosolic protein associated with the trans-Golgi network (TGN) and the keratin cytoskeleton. GALNS encodes a lysosomal hydrolase necessary for the degradation of glycosaminoglycans. PEX1, PEX6, and PEX26 are necessary for peroxisome biogenesis. SLC13A5 encodes a membrane citrate channel providing citrate influx proximally and efflux (into the enamel matrix) distally. Small secretory vesicles (magenta) in the proximal and distal parts of the Tomes’ process (distally) secrete AMELX, AMBN, ENAM, and MMP20 at the rod and interrod growth sites. Thin lines in the extracellular matrix (bottom) represent the general direction of enamel mineral ribbons. Not shown: CACNA1C encodes an L-type (voltage-dependent calcium channel) thought to provide regulated Ca²⁺ influx. SLC10A7 encodes a transmembrane transporter of unknown specificity that causes severe enamel defects when mutated. Graphic by Shelly Zhang.