BSPRY (B-box and SPRY domain containing protein) is a regulatory protein primarily involved in epithelial calcium homeostasis and early embryonic development. Functionally, BSPRY serves as a negative regulator of epithelial calcium transport by inhibiting TRPV5 (transient receptor potential vanilloid 5) channel activity 1. BSPRY interacts directly with TRPV5 and reduces calcium influx in kidney epithelial cells without affecting channel surface expression, suggesting it acts as an intracellular modulator of channel function 1. The protein is part of a coordinated regulatory network alongside calbindin-D28k and klotho that collectively controls calcium homeostasis at multiple cellular levels 2. BSPRY expression is inversely regulated by vitamin D3, indicating involvement in calciotropic hormone signaling 1. Beyond calcium regulation, BSPRY maintains embryonic stem cell pluripotency; knockdown reduces undifferentiated colonies while overexpression increases them, and manipulation of BSPRY levels affects early embryonic development and inner cell mass formation 3. The protein contains structural domains (B-box and SPRY) characteristic of proteins involved in innate immunity 4, and genetic variants near BSPRY show association with cleft lip and palate, suggesting roles in facial development 5. These findings position BSPRY as a multifunctional regulatory protein linking calcium metabolism, embryonic development, and potentially immune processes.