Testis

Indirect Sertoli Cell-Mediated Ablation of Germ Cells in Mice Expressing the Inhibin- Promoter/Herpes Simplex Virus Thymidine Kinase Transgene

Abstract
In the present study, we describe a novel mouse model for inducible germ cell ablation. The mice express Herpes Simplex virus thymidine kinase (HSV-TK) under the inhibin- subunit promoter (Inh). When adult TG mice were treated with famciclovir (FCV) for 4 weeks, their spermatogenesis was totally abolished, with only Sertoli cells and few spermatids remaining in the seminiferous tubules. However, testicular steroidogenesis was not affected. Shorter treatment periods allowed us to follow up the progression of germ cell death: After 3 days, spermatogonia and preleptotene spermatocytes were no longer present. After 1-week treatment, spermatogonia, preleptotene and zygotene spermatocytes were missing, and the amount of pachytene spermatocytes was decreased. After 2-week treatment, round and elongating spermatids were present. During the third week, round spermatids were lost and finally, after 4-week treatment, only Sertoli cells and few spermatids were present. Interestingly, the transgene is detected in Leydig and Sertoli cells, but not in spermatogonia. This suggests that FCV is phosphorylated in Sertoli cells, and thereafter, leaking to neighboring spermatogonia, apparently through cell-cell junctions present, enabling trafficking of phosphorylated FCV. Because of the many mitotic divisions they pass through, the spermatogonia are very sensitive to toxins interfering with DNA replication, while non-dividing Sertoli cells are protected. Using transillumination-assisted microdissection of the seminiferous tubules, the gene expression patterns analyzed corresponded closely to the histologically observed progression of cell death. Thus, the model offers a new tool for studies on germ cell-Sertoli cell interactions by accurate alteration of the germ cell composition in seminiferous tubules.

Key words: Testis • Sertoli cells • Spermatogenesis