. Development and characterization of somatic cell testicular tumors in transgenic mice. A common precursor for Leydig and Sertoli cell neoplasms?.

QUINTANA S; VENARA M.; REY R; DUTERTRE M; DI CLEMENTE N; PICARD J.Y; XAVIER F.; CHEMES H.

Baeza

Workshop; Workshop on ?Germ Cell-Soma Interactions In Gonadal Development and Germ Cell Tumou; 2008

Transgenic mice bearing a construct in which the expression of the SV40 oncogen is directed by the AMH promoter (AT mice) develop testicular tumors in adult life. We studied early steps of tumor development and characterized these tumors at different ages by means of histologic, morphometric immunohistochemical and molecular techniques. 1-3 month-old AT mice depicted multifocal Leydig cell hyperplasia. The Leydig cell volume was higher in some transgenic animals in comparison with littermate controls. Between 5½ and 7 months microscopic interstitial tumors developed in some AT mice. These microtumors progressively developed and at 7-14 months of life formed large confluent areas of high mitotic index. Tumor cells had the phenotypic characteristics of Leydig cells, or formed solid cord-like structures reminiscent of those seen in Sertoli cell tumors. Both hyperplastic areas and tumors expressed 3-hydroxysteroid dehydrogenase (3-HSD) and inhibin -subunit in the Leydig cell areas. AMH expression was negative in Leydig cell-like regions and variable in Sertoli cell-like areas. The large T antigen of SV40 (SV40 T) and markers of cell proliferative activity (PCNA) were intensely positive in hyperplastic cells and tumors. Control mice of similar ages showed neither hyperplasia nor tumors, and SV40 T expression was always negative. In conclusion, many adult AT mice develop large testicular tumors that are preceded by interstitial hyperplasia and microtumors. The histologic and immunohistochemical phenotype of tumors in AT mice (Leydig and Sertoli cell differentiation, positive 3-HSD and  Inhibin and variable AMH) suggests a mixed differentiation of somatic cells of the specialized gonadal stroma. The interesting finding that an oncogen directed by a promoter specifically active in early fetal Sertoli cells has given rise to testicular tumors of mixed differentiation is compatible with a common origin of Leydig and Sertoli cells from the specific stroma of the gonadal ridge. To test this hypothesis we have recently studied 11-14 day old male embryos at the time of testicular differentiation using markers of Sertoli cells (Wilms Tumor antigen WT1, SOX 9 and AMH), Leydig cells (3b-HSD) and the transgen SV40T. As anticipated, AMH, WT1 and SV40T were present in all fetal Sertoli cells, and 3b-HSD was positive in all Leydig cells of control and transgenic embryos. Unexpectedly, SV40T was also focally expressed in some Leydig cells. These SV40T-positive Leydig cells were present at all fetal ages and in hyperplasias or tumors of postnatal trangenic mice suggesting that fetal Leydig cells modified by the expression of the transgene were the origin of postnatal hyperplasias and tumors. The positive expression of AMH-promoter-driven SV40T in fetal Leydig cells strongly suggests either a common origin for Leydig and Sertoli cells or a transdifferentiation process from early Sertoli cells to Leydig cells. Current efforts in our laboratory have resulted in the successful isolation of RNA transcripts from areas in paraffin tissue sections that depicted specific differentiation patterns both in control and transgenic mice. These RNA transcripts can be retrotranscribed and amplified by PCR to study gene expression. Further efforts to characterize the origin of tumors as well as the mechanisms of hyperplasia and tumorigenesis in these animals are currently under way. Supported by Grants from CONICET (PIP 2565/00 and 5479), ANPCyT (PICT 9591) and INSERM-CONICET International Cooperation Program.