Over-expression of Müllerian inhibiting substance mRNA in the Turner syndrome ovary.

Turner Syndrome (TS) is a disorder of human females associated with complete or partial loss of one of the X chromosomes, varying degrees of multiple congenital malformations and gonadal dysgenesis. However, the reason for the premature loss of germ cells in the TS ovaries is currently unknown. To understand the molecular basis of the gonadal dysgenesis the mRNA expression of Mullerian Inhibiting Substance (MIS) was examined in human fetal and adult TS ovaries and compared with normal ovaries by in situ hybridization. The expression of MIS was found to be increased in the granulosa cells of the TS ovaries as compared to that in normal ovaries, and these granulosa cells were organized to form testicular tubule like structures. MIS was also found to be ectopically expressed in the oocytes of the developing TS gonads. The stromal cells of the streak gonads of adult TS women abundantly expressed MIS. We speculate that the absence of a second X chromosome leads to over-expression of MIS that may be co-responsible for failure of ovarian differentiation in TS. MIS may be a potential negative regulator of ovarian development in humans.