Molecular biology of ureteral bud and trigonal development.

Advances in molecular biology have provided valuable insight into the development of the urinary tract, particularly ureteral bud formation. Reciprocal inductive signals between the ureteral bud and growing kidney are crucial for normal development. The Wolffian duct serves as the site of origin of the ureteral bud and forms distal excretory ducts that are incorporated into the developing bladder to become the trigone. Vesicoureteral reflux and renal dysplasia can result from abnormal position of the ureteral orifice on the trigone. The presumed origin of trigone formation is based largely on evaluation of human and animal models performed nearly a century ago. The trigone is thought to develop from the mesodermal germ cell layer; however, several recent studies have shown that endoderm may be the tissue of origin. This review highlights important discoveries in the field of molecular biology as it relates to the development of normal and abnormal ureteral bud formation. It also describes the anatomic relationship between the developing bud and trigone as it pertains to clinically relevant urinary tract anomalies, including recent discoveries that attempt to prove the origin of the trigone.