Involvement of insulin-like factor 3 (Insl3) in diethylstilbestrol-inducedcryptorchidism

Recently, it has been shown that targeted inactivation of the Insl3 gene in male mice results in cryptorchidism. The Insl3 gene encodes insulin-like f actor 3 (lnsl3), which is expressed in fetal Leydig cells. The testicular f actor Insl3 appears to play an important role in the transabdominal phase o f testis descent, which involves development of the gubernaculum. Other stu dies have demonstrated that in utero exposure to diethylstilbestrol (DES), a synthetic estrogen, can lead to cryptorchidism both in humans and in anim al models. The present study was undertaken to investigate whether prenatal DES-exposu re might interfere with testicular Insl3 mRNA expression. Furthermore, the effect of DES on steroidogenic factor 1 (SF-1) mRNA expression level was de termined, since it has been shown that SF-1 plays an essential role in tran scriptional activation of the Insl3 gene promoter. Timed pregnant mice were treated with DES (100 mu g/kg body weight) or vehicle alone on days E9 (ge stational day 9) through E17. Control and DES-exposed mouse fetuses were co llected at E16, E17 and E18, when transabdominal testis descent is taking p lace. Lack of gubernaculum development in DES-exposed animals was confirmed by histological analyses at E17. Expression of Insl3 and SF-1 mRNAs was st udied in testes of control and DES-exposed fetuses at E16 and E18 by RNase protection assay. Prenatal DES-exposure resulted in a three-fold decrease i n Insl3 mRNA expression level (P < 0.005), at both E16 and E18. In contrast , DES treatment had no effect on the expression of SF-1 mRNA. These results support our hypothesis that DES may interfere with gubernaculum developmen t by altering Insl3 mRNA expression, providing a possible mechanism by whic h DES may cause cryptorchidism.