The polycystin family includes polycystin-1 (PKD1), polycystin-2 (PKD2), their related proteins (such as PKD1L1, PKD1L2, PKD1L3, PKD2L1, and PKD2L2), and the polycystin family receptor for egg jelly (PKDREJ). Polycystins typically function as non-selective cation channels or components of receptor-ion channel complexes, and are often permeable to calcium [, ]. PKD1 and PKD2 form a heterotetrameric complex in the primary cilium of renal epithelial cells, where they are involved in fluid-flow mechanosensation and the regulation of intracellular calcium signalling [, , ]. Mutations in either PKD1 or PKD2 cause autosomal dominant polycystic kidney disease (ADPKD) [, ]. Other family members have diverse roles: PKD1L3 and PKD2L1 form a heteromeric channel activated by low pH, which may act as a sour taste receptor [, , ]; PKDREJ is a testis-specific protein that controls sperm transport and the acrosome reaction []; and PKD1L2 may function as a G protein-coupled receptor []. Structurally, polycystins contain multiple transmembrane helices, and many members possess a conserved polycystin cation channel domain [].
