The effect of donor age on progression of spermatogenesis in canine testicular tissue after xenografting into immunodeficient mice

The objective of this study was to examine the effect of donor age on progression of spermatogenesis in dog (Canis lupus familiaris) testis tissue after xenografting. In Experiment 1, canine testes were obtained by surgical castration. Based on developmental pattern of spermatogenesis at the time of grafting, donors were categorized as immature, young, and adult (<4, 4 to 6, and >6 mo old, respectively). Fragments of testis tissue were implanted subcutaneously on the back of immunodeficient mice; xenografts were retrieved and analyzed 4, 6, or 8 mo later. At 4 mo postgrafting, immature and young groups had higher graft recovery rates, graft weights, vesicular gland indices, seminiferous tubule numbers, and larger seminiferous tubular diameters compared with those of adult donor xenografts. At 8 mo postgrafting, immature donor xenografts had maintained growth and development as exhibited by greater graft weights, vesicular gland indices, seminiferous tubule numbers, and tubular diameters compared with those of adult donor xenografts. At this time point, growth and development of xenografts did not differ between immature and young donors, whereas those from young donors had greater seminiferous tubule numbers and diameters compared with those of adult donor xenografts. Elongated spermatids were the most advanced germ cell type present at 4 and 8 mo postgrafting in xenografts of immature age groups. In Experiment 2, the longer-term efficiency of spermatogenesis and the potential sperm production in xenografts from immature donor dogs were determined. Testis tissue from 2-mo-old donor dogs were grafted into recipient mice, and xenografts were retrieved after 13 mo. Complete spermatogenesis was present in 5 of 29 recovered xenografts, with isolation of fully formed sperm (up to 36.3 × 10⁶ per gram tissue). In conclusion, immature and young donors (<6 mo of age) were the most promising donors for dog testis tissue xenografting. This strategy may offer an alternative for male germ-line preservation for canids that die prematurely or must be castrated before maturation.