DiI analysis of cell migration during müllerian duct regression

In most male vertebrates, the müllerian ducts, which are the embryonic oviducts, regress completely during embryogenesis or shortly thereafter. Müllerian duct regression is caused by the testicular hormone müllerian inhibiting substance. While the exact mechanism of müllerian duct regression is not well understood, it is theorized to involve active migration of at least some of the ductal epithelial cells following breakdown of the basement membrane, possibly through an interaction between the epithelial cells and the surrounding extracellular matrix. The purpose of the present study was (1) to confirm that müllerian duct regression is characterized by epithelial cell migration and (2) to determine the destination of these cells. The ductal epithelium of male alligator embryos was labelled with the fluorescent cell marker DiI and then allowed to undergo regression in vitro. DiI-labeled müllerian ducts from female embryos served as controls. An in vivo experiment also was performed in which the müllerian ducts of female hatchlings were injected with DiI prior to each female receiving a testicular implant from a male hatchling. Control females received a kidney implant instead. In both the in vitro and the in vivo experiments, DiI-labeled epithelial cells were observed migrating out from the duct during regression. In the in vitro experiment in which regression proceeded more rapidly, epithelial cells entered the mesonephric kidneys and were incorporated into the nephric tubule epithelium. No regression or cell migration was observed in the control müllerian ducts.