Somatic cell exchange occurs between mouse fetal gonads and mesonephroi during in vitro culture

Mesonephric cell contribution to the developing mouse gonad has previously been shown to be male-specific in in vitro culture models. This study shows that somatic cell exchange occurs between fetal mouse mesonephroi and gonads during in vitro culture of assembled tissues. Assembling gonads with cell marker-carrying mesonephroi and vice versa identified cell exchange. Two different cell markers were used. One of the markers was the thymidine analogue bromodeoxyuridine (BrdU), which was added to the culture medium during an initial culture period before in vitro culture of assembled tissues in medium without BrdU. The other was bacterial beta-galactosidase, which is expressed ubiquitously in tissues from the transgenic mouse strain ROSA26. The tissues were taken from either 10.5- or 11.5-day-old mouse fetuses, and the assembled tissues were cultured for 36-60 h. Both cell markers demonstrated the occurrence of a cell exchange in both directions between the mesonephros and the gonad. The cell contribution was found to be minor and independent of the initial age of the tissue and hours in culture. Further, mesonephric cell contribution was not male-specific. Cell exchange between the two tissues may be due to growth between the assembled tissues rather than active signal-regulated migration. It is suggested that in vitro culture models may not be applicable for investigating mesonephric cell contribution to the developing mouse gonad.