The length of the spermatogenic cycle is conserved in porcine and ovine testis xenografts.

Xenografting of immature mammalian testis tissue into mice can accelerate sperm production. To determine whether this shortened time to sperm production is because of reduced length of the spermatogenic cycle, we applied bromodeoxyuridine (BrdU) incorporation to analyze the spermatogenic cycle in porcine and ovine testis xenografts. Small testis fragments from newborn pigs and sheep were ectopically grafted into mice. Once complete spermatogenesis was present in grafted tissue, mice were injected with BrdU and grafts were recovered at different time points thereafter. In porcine grafts, the most advanced germ cells labeled 1 hour, 9 days, 12.3 days, and 18 days after BrdU injection were stage 1 preleptotene/leptotene primary spermatocytes, stage 1 pachytene primary spermatocytes, stage 5 newly-formed round spermatids, and late stage 2 elongating spermatids, respectively. In ovine grafts, the most advanced labeled germ cells at 1 hour, 11 days, and 22 days post-BrdU injection were stage 2 preleptotene/leptotene primary spermatocytes, late stage 1 pachytene primary spermatocytes, and stage 2 elongating spermatids, respectively. These results indicate that each spermatogenic cycle in porcine and ovine xenografts lasts approximately 9 and 11 days, respectively, which is similar to their durations in situ. Therefore, the length of the spermatogenic cycle is conserved in porcine and ovine testis xenografts. This is consistent with earlier reports showing that the cycle length is inherent to the germ cell genotype. The shortened time to sperm production in xenografts therefore appears attributable to accelerated maturation of the testicular somatic compartments. Our results suggest that testis xenografts provide a useful model to study the timing of testicular maturation and spermatogenesis in different mammalian species.