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，又可用于保存男性性腺功能。这项技术最近被用来区分不同物种的新生儿睾丸，达到完全精子发生的水平，然而，普通绒猴(Callithrix Jacchus)的移植睾丸的精子发生并不超过精原阶段。本研究以NOD/SCID/γ小鼠为受体，研究了未成熟绒猴睾丸在异位移植中的生精恢复情况。方法：雄性去势NOG小鼠分别接受新生(0d龄)和幼年(7月龄)绒猴5~8只睾丸移植。两到七个月后，从受者身上取出移植物，并检查移植物的数量、大小和组织学。结果和讨论：新生儿移植物存活率为87%(13/15)，婴儿移植物存活率为75%(24/32)。新生绒猴的睾丸组织在7个月内发育到分化的精原细胞(A型和B型)，有少量的早期精母细胞，而移植前的精原细胞主要是未成熟的精原细胞(生殖细胞)。在体内，新生睾丸移植物的精子生成水平与对照睾丸相当，甚至更高。另一方面，幼猴的生精恢复有限，生殖细胞可能停留在次级精母细胞阶段，而在年龄匹配的对照睾丸中观察到精子细胞。绒猴睾丸移植物的精子发生并不完全成功，但本研究的精子恢复率和移植物发育情况均优于其他作者报道的结果。使用NOG小鼠作为受体，可提高异位移植的移植物存活率和调节睾丸发育。

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.