Retinoschisin Is Required for Pineal Gland Calcification and Cellular Communication in Pinealocytes of Rats and Mice

Retinoschisin (RS1) is a secretory protein specifically localized to the extracellular domains in both the lateral retina and the pineal gland (PG). However, the functions of RS1 in the pineal body are poorly understood. To address this knowledge gap, in this study, we undertook histochemical, ultrastructural, and Western blotting analyses of the PG in rats and RS1-knock-in transgenic. We found that RS1 plays a key role in pineal gland calcification (PGC) in mice through both extracellular and intracellular pathways. RS1 was clustered around the cell membrane or intracellularly in pinealocytes, actively participating in the exchange of calcium and thereby mediating PGC. Additionally, RS1 deposition is essential for maintaining PGC architecture in the intercellular space of the adult PG. In RS1-knock-in mice with a nonsense mutation (p.Y65X) in the Rs1-domain of RS1, the Rs1-domain is chaotically dispersed in pinealocytes and the intercellular region of the PG. This prevents RS1 from binding calcified spots and forming calcified nodules, ultimately leading to the accumulation of calcareous lamellae in microvesicles. Additionally, RS1 was observed to colocalize with connexin-36, thereby modulating intercellular communication in the PG of both rats and mice. Our study revealed for the first time that RS1 is essential for maintaining PGC architecture and that it colocalizes with connexin 36 to modulate intercellular communication in the PG. These findings provide novel insights into the function of the RS1 gene in the PG.