205 A GAME OF CAT AND MOUSE: XENOGRAFTING OF TESTIS TISSUE FROM DOMESTIC KITTENS RESULTS IN COMPLETE CAT SPERMATOGENESIS IN A MOUSE HOST

Abstract

Loss of genetic diversity due to infertility or the premature death of valuable individuals is a significant problem in the conservation of rare and endangered felid species, as well as in the maintenance of lines of cats used to study inherited feline and human disease. Attempts to overcome loss of genetic diversity have focused on freezing sperm;; however, sperm cannot be collected from immature males. Previously, we reported completion of spermatogenesis in testis tissue from newborn pigs and goats grafted ectopically into host mice (Honaramooz A et al., 2002 Nature 418, 778–781). Xenografting of testis tissue not only serves as a powerful system for the study of spermatogenesis and testicular maturation, but it also provides a previously unavailable system to obtain sperm from immature animals. The objective of the present study was to extend the technique of testis tissue xenografting to the domestic cat as a model animal for felid species. Testes from 1- to 5-wk-old domestic short-haired kittens (n = 8) were cut into small fragments (about 1 × 3 mm each), and up to eight fragments were grafted under the back skin of each castrated immunodeficient host mouse (n = 12). Histological examination of the testis xenografts was performed between 14 and 36 weeks post-transplantation. From 8 of the 12 recipient mice, 93% of testis tissue grafts were recovered. No grafts were recovered from the remaining 4 mice. At the time of grafting, the seminiferous cords of the donor testis tissue contained only immature Sertoli cells and gonocytes. At 14 weeks after grafting, tubular expansion was evident, caused by the proliferation of Sertoli cells and tubular lumen formation. By 18 weeks after transplantation, the seminiferous epithelium contained spermatocytes, and by 20 weeks, round spermatids were the most advanced types of germ cells. By 36 weeks after transplantation, xenografts of cat testis tissue had completed spermatogenesis and mature sperm were present. In all recipient animals where xenografts were recovered, the weight of the seminal vesicles in the castrated host mice was restored to pre-castration values, indicating that xenografts were capable of releasing biologically active testosterone. These results demonstrate the potential of xenografting to achieve full spermatogenesis in testis tissue from kittens without the necessity of exogenous hormonal stimulation. It was shown previously that sperm recovered from testis xenografts can support fertilization and development (Shinohara T et al., 2002 Hum. Reprod. 17, 3039–3045; Schlatt S et al., 2003 Biol. Reprod. 68, 2331–2335). Therefore, sperm production in a mouse host can provide an alternative for germ line preservation from immature felids where sperm cryopreservation is not an option. Sperm recovered from xenografts can be used for assisted reproduction, thereby making it possible to produce offspring from immature males.