PKD2 and polycystic kidney disease: Male worm mating relies on polycystin-2 (PKD-2), homologous to the human polycystic kidney disease gene PKD2, which is expressed in male-specific sensory neurons, including the cephalic male neurons (CEMs) in the head (Fig. 1a), type B ray neurons (RnBs) in the rays, and hook type B neurons (HOBs) in the hook34,35.