Establishment of fetal gonad/mesonephros coculture system using EGFP transgenic mice

In developing mouse embryos, the Sertoli cells, Leydig cells, and seminiferous cords are differentiated in the XY gonads. The migration of mesonephric cells into the gonads is required during the developmental stage for seminiferous cord formation in the male gonads. In previous experiments, an organ coculture system has been used to examine morphologically developing gonads. However, by the process used in this system for fixing and staining the gonad/mesonephros complexes for examination, the kinetics of cell migration and the character of migrating cells cannot be observed. In the present study, we established an improved organ coculture system, using transgenic mice ubiquitously expressing Enhanced Green Fluorescent Protein (EGFP). In this system, time-dependent morphological changes in male-specific migration were observable in the gonad/mesonephros complex. The cell migration occurred at around 20 hr of coculture and began to spread at 25 hr with increases in the number of migrating cells occurring at 45 hr of coculture. No degenerative changes were detected at the end of coculture. Our results indicate that the present coculture system is very useful for investigating the mechanism of cell migration, as well as the characteristics of the migrating cells, in developing gonads. J. Exp. Zool. 286:320-327, 2000.