A Model to Study Human Ovotesticular Syndrome
Laurence Baskin, MD, Yi Li, MD, Mei Cao, MD, Sena Askel, MD, Gerald Cunha, PhD.
UCSF, San Francisco, CA, USA.
BACKGROUND: Ovotesticular syndrome is a rare disorder of sex development characterized by the presence of testicular and ovarian tissue within the same gonad. The histologic characteristics of human testicular tissue are well defined by the presence of seminiferous tubules containing germ cells and SOX9-positive Sertoli cells surrounded by interstitial tissue containing cytochrome P450-positive Leydig cells and smooth muscle α-actin-positive peritubular myoid cells. The histological characteristics of the ovary can be defined by germ cell nests and follicles. In contrast to the testis, the ovary has a paucity of defined specific protein markers, with the granulosa cell marker FOXL2 being the most widely used. Ovarian stroma is not well defined. In practice, defining the ovarian component of the ovotestis can be quite difficult.
Methods: We developed a model of human ovotesticular syndrome by combining fetal human testis and ovary in two types of xenografts: 1) A bipolar model; placing a small piece of testicular tissue next to ovarian tissue and 2) An admixed model; mincing up testicular and ovarian tissue and grafting the mixture together. (Figure 1) Both types of ovotesticular xenografts were grown under the renal capsules of castrate athymic nude mice for 6 - 32 weeks along with age matched control grafts of human fetal testis and ovary. Fifty ovotesticular xenografts and their controls were analyzed by histology, immunohistochemistry, and fluorescent in situ hybridization to determine the protein expression and karyotype of the cells within the grafts.
Results: The ovotesticular xenografts exhibited recognizable testicular and ovarian tissue based on testis specific and ovarian specific markers defined above. The bipolar xenografts simulated a bipolar ovotestis in which the testicular and ovarian elements retain their separate histological characteristics and are separated by a microscopic border (Figure 2). In contrast, the admixed grafts showed mixed areas of healthy ovarian follicles and seminiferous cords (Figure 3). We were not able to define specific markers to identify the ovarian stroma in these grafts highlighting the nonspecific nature of the ovarian stromal component. The juxtaposed seminiferous tubules and follicles exhibited normal morphology.
Conclusion: We have characterized a human model of both bipolar and admixed ovotestis which will allow a deeper understanding of ovotestis development in humans and facilitate a more accurate diagnosis of ovotesticular syndrome. In our experimental model, it appears impossible to separate testicular and ovarian tissue in the admixed mode and difficult, at best, in the bipolar model.
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