Development of an in vivo experimental system for spermatogenesis by ectopic grafting of marmoset testis tissue into immunodeficient mice

背景：免疫缺陷小鼠睾丸组织异位移植是一种新的实验系统，既可用于研究精子发生，又可用于保护雄性性腺功能。该技术最近被用于区分不同物种的新生儿睾丸，直到完全精子发生的水平，然而，普通狨猴（Callithrix jacchus）睾丸移植的精子发生不会超过精原阶段。在本研究中，我们使用NOG小鼠（NOD/SCID/γ - cnull）作为受体，研究了未成熟绒猴睾丸异位移植的生精恢复情况，NOG小鼠被认为是移植人类正常细胞的良好动物模型。方法：雄性阉割的NOG小鼠分别接受新生（0日龄）和幼龄（7月龄）狨猴的5个或8个睾丸移植。2至7个月后，从受者身上取出移植物，检查它们的数量、大小和组织学。结果与讨论：新生儿移植成活率为87%(13/15)，婴儿为75%（24/32）。新生狨猴的睾丸组织在7个月左右发育到分化精原细胞阶段（a型和B型），其中含有少量的早期精母细胞，移植前主要含有未成熟的精原细胞（性腺细胞）。新生儿睾丸移植物的精子发生水平与体内对照睾丸相当或更先进。另一方面，婴儿狨猴的精子发生恢复受到限制，生殖细胞可能在次级精母细胞阶段被阻止，而精子在年龄匹配的对照睾丸中被观察到。虽然狨猴睾丸移植后精子发生不完全，但本研究的恢复率和移植物发育均优于其他作者的报道。以NOG小鼠为受体可改善异位移植中移植物的存活和睾丸发育的调节。

Background: Ectopic grafting of testicular tissue into immunodeficient mice is a new experimental system that can be used not only to study spermatogenesis but also to preserve male gonadal function. This technique has been used recently to differentiate the neonatal testes of different species up to the level of complete spermatogenesis, however, spermatogenesis in testicular graft from common marmoset (Callithrix jacchus) does not proceed beyond the spermatogonial stage. In this study we examined spermatogenic recovery of immature marmoset testis in ectopic grafts using NOG mice (NOD/SCID/γcnull) as recipients, which are known as an excellent animal models for engraftment of human normal cells. Methods: Male castrated NOG mice received five or eight testicular grafts from newborn (0 day old) and infant (7 months old) marmosets. Two to seven months later, grafts were removed from the recipients and their numbers, size, and histology were examined. Results and discussion: Graft survival rate was 87%(13/15) for the newborn and 75%(24/32) for the infant. Testicular tissues from a newborn marmoset developed up to the stage of differentiated spermatogonia (A type and B type) with a small amount of early spermatocytes in seven months, whereas they mainly contained immature spermatogonia (gonocytes) before grafting. The level of spermatogenesis in grafts from newborn testis was comparable to, or more advanced than, that in the control testis in vivo. On the other hand, spermatogenesis recovery was limited in infant marmosets, arresting the germ cells probably at the stage of secondary spermatocytes, while spermatids were observed in age-matched control testis. Complete spermatogenesis in testicular grafts from marmosets did not succeed, however, recovery rate and graft development in the present study were superior to those reported by other authors. Using NOG mice as recipients might improve graft survival and conditioning of testicular development in ectopic grafting.