309 THE SPERMATOGENIC CYCLE IN MAMMALIAN TESTIS XENOGRAFTS

Abstract

Grafting of immature testis tissue from different mammalian donor species into mouse hosts results in production of spermatozoa from the donor species. Xenografting of testis tissue from rhesus monkeys, pigs, and sheep accelerates sperm production. To determine whether this shortened time to sperm production is due to the reduced spermatogenic cycle length, we applied bromodeoxyuridine (BrdU) incorporation to analyze the spermatogenic cycle in porcine and ovine testis xenografts. Testes from 1-2-week-old Yorkshire cross pigs and 1-week-old Suffolk sheep were cut into small fragments (approximately 1 × 1 × 2 mm) and eight fragments were grafted under the back skin of each castrated male immunodeficient NCR nude recipient mouse (n = 7 for pig, n = 5 for sheep). Mice were given BrdU (100 mg/kg i.p.) at 7 months (porcine tissue) or 6 months (ovine tissue) post-transplantation. Mice carrying porcine tissue were sacrificed 1 h, 9 days or 18 days after BrdU injection. Mice with ovine testicular tissue were sacrificed 1 h, 11 days or 22 days after BrdU injection. Analysis time points were chosen based on the reported length of the spermatogenic cycle in pigs and sheep (approximately 9 days and 11 days, respectively). All eight stages of the spermatogenic cycle were analyzed to identify the most advanced germ cells labeled in each time period after BrdU injection. All seminiferous tubules containing full spermatogenesis were analyzed. Histologically, 51.8% (range 7 to 98%, n = 2040 tubules) of seminiferous tubules from porcine grafts, and 64.4% (range 2 to 92%, n = 2903 tubules) of seminiferous tubules from ovine grafts presented complete spermatogenesis. In porcine grafts, the most advanced germ cells labeled 1 h after BrdU injection were primary spermatocytes in pre-leptotene/leptotene at stage I of the spermatogenic cycle. At 9 days and 18 days after injection, the most advanced labeled germ cells were primary spermatocytes at pachytene at stage I and elongating spermatids at late stage II, respectively. In ovine grafts, the most advanced labeled germ cells at 1 h, 11 days and 22 days were pre-leptotene/leptotene at stage II, primary spermatocytes at the pachytene at stage I and elongating spermatids at stage II, respectively. These results indicate that each spermatogenic cycle in porcine and ovine testis xenografts lasts around 9 days and 11 days, respectively. Therefore, the length of the spermatogenic cycle is conserved in porcine and ovine testis xenografts and shortened time to sperm production is likely due to accelerated maturation of the testicular somatic components, such as Sertoli cells.

This work was supported by NIH R01 RR17359-01.