Fetal Ovotestes in XX⇔XY Chimeric Mice Develop into Testes in Adults

Abstract

It has been accepted that the majority of XX⇔XY chimeric mice develop into adult males. The present study was designed to examine the gonads of XX⇔XY chimeric mice to determine whether the co-existence of chromosomally female (XX) and male (XY) cells affects sex differentiation. Southern blot analysis using a Y chromosome specific DNA fragment as a probe revealed the sex chromosomal constitution of C57BL/6N⇔DDD/1 chimeric mice. The histological features of the gonads in XX⇔XY chimeric mice were observed at both fetal and adult stages. The gonads in XX⇔XY chimeras were ovotestes at the fetal stage on 15 days post coitum (d.p.c.), had predominantly testicular components after 16 d.p.c., and were testes at adult stage. This observation indicates that the fetal ovotestes in XX⇔XY chimeras develop into testes in adults. In addition, testes of some adult chimeras which were not dominantly composed of XY cells showed co-existence of gametic and agametic seminiferous tubules.