Xenografting of isolated equine (Equus caballus) testis cells results in de novo morphogenesis of seminiferous tubules but not spermatogenesis

The study of spermatogenesis in the horse is challenging because of the absence of an in vitro system that is capable of reproducing efficient spermatogenesis and because of the difficulties and costs associated with performing well-controlled studies in vivo. In an attempt to develop novel methods for the study of equine spermatogenesis, we tested whether cells from enzymatically digested pre-pubertal equine testicular tissue were capable of de novo tissue formation and spermatogenesis following xenografting under the back skin of immunocompromised mice. Testes were obtained from normal pre-pubertal colts and dissociated into cell suspensions using trypsin/collagenase digestion. Resulting cell pellets, consisting of both somatic and germ cells, were injected into fascial pockets under the back skin of immunocompromised, castrated mice and maintained for between 1 and 14 months. Mice were killed and grafts were recovered and analyzed. As has been reported for testis cell suspensions from pigs, mice, cattle, and sheep, de novo formation of equine testicular tissue was observed, as evidenced by the presence of seminiferous tubules and an interstitial compartment. There was an increased likelihood of de novo testicular formation as grafting period increased. Using indirect immunofluorescence, we confirmed the presence of spermatogonia in de novo formed seminiferous tubules. However, we found no evidence of meiotic or haploid cells. These results indicate that dissociated pre-pubertal equine testis cells are capable of reorganizing into the highly specialized endocrine and spermatogenic compartments of the testis following ectopic xenografting. However, in spite of the presence of spermatogonia within the seminiferous tubules, spermatogenesis does not occur. Although this technique does allow access to the cells within the seminiferous tubule and interstitial compartments of the equine testis prior to reaggregation, the absence of spermatogenesis will limit its use as a method for the study of testicular function in the horse.