S100P expression in the human embryo. S100P is expressed in the right and left horns of the urogenital sinus (RUGS and LUGS), as well as in the bladder portion of the urogenital sinus (indicated by arrow) in CS17 (A, B), as well as in the allantois (C). In CS21 (D), S100P in the urethral portion of the urogenital sinus (E) shows stronger immunoreactivity than in the bladder portion (F). In the kidney, expression of S100P is seen in the renal pelvis (G, H) as well as in the glomerulus (I) in PCW10. Further expression is seen in the gastrointestinal tract (J-L), including the gallbladder (indicated with arrow) (K) as well as the stomach and pylorus (I) in CS23.