Abstract
Testicular development in camelids is remarkably variable between individuals. This variation may contribute to high incidences of testicular cysts, testicular hypoplasia and degeneration observed in camelids. Multiple factors can contribute to testicular dysgenesis including improper germ cell differentiation, or disrupted rete testis and genetic factors. We initiated a study with alpacas to determine if ectopic testis tissue xenografting is an effective model to investigate testis development in camelids. The objective of this study was to evaluate development of testicular tissue from pre-pubertal alpacas xenografted onto castrated nude mice. We hypothesized that testicular tissue from 8-month-old alpaca would result in the most effective establishment of spermatogenesis follow grafting due to the presence of only undifferentiated spermatogonia at this age. Testis tissue from alpacas at 6, 7, 8, 9, and 10 months (n=4 per age) were xenografted onto three nude mice per donor. Each recipient mouse had four testis explants (5-10mg) grafted onto the back and grafts were harvested 24 weeks later. Analysis consisted of evaluation of recipient mouse serum testosterone, testis graft weights and histological examination of grafts. Serum testosterone concentration was highest (3.35 ng/ml) in recipient mice grafted with 8-month-old donor tissue and the lowest (0.51ng/ml) in recipients with 7-month-old donor tissue. Whereas the vesicular gland weights were greatest (363 mg) in mice grafted with 6-month-old donor tissue. Graft survival and collection ranged from 75% to 100% and functional grafts that contained active differentiated germ cells ranged from 87.5% to 100%. No significant differences were detected in graft weights in mice grafted with testis tissue from different aged donors. The percentage of seminiferous tubules in grafts with elongating spermatids was 6.2, 6.1, 0.9, and 0.8% from donor alpacas aged 6,7,8,9 months, respectively. In contrast, grafts from 10-month-old donors contained only primary spermatocytes (96.7%) as the most advanced germ cells. Additionally, 6-month-old donor grafts showed the greatest overall percentage (87.5%) of grafts that produced elongated spermatids. Xenografting of alpaca testes produced testosterone and was successful to stimulate maturation of pre-pubertal testes to produce elongated spermatids. Thus, this approach can be used as a model to study disrupted spermatogenesis in camelidae.