Pattern and kinetics of mouse donor spermatogonial stem cell colonization in recipient testes

Recently a system was developed in which transplanted donor spermatogonial stem cells establish complete spermatogenesis in the testes of an infertile recipient. To obtain insight into stem cell activity and the behavior of d onor germ cells, the pattern and kinetics of mouse spermatogonial colonizat ion in recipient seminiferous tubules were analyzed during the 4 mo followi ng transplantation. The colonization process can be divided into three cont inuous phases. First, during the initial week, transplanted cells were rand omly distributed throughout the tubules, and a small number reached the bas ement membrane. Second, from 1 wk to 1 mo, donor cells on the basement memb rane divided and formed a monolayer network. Third, beginning at about 1 mo and continuing throughout the observation period, cells in the center of t he network differentiated extensively and established a colony of spermatog enesis, which expanded laterally by repeating phase two and then three. An average of 19 donor cell-derived colonies developed from 10(6) cells transp lanted to the seminiferous tubules of a recipient testis; the number of col onized sites did not change between 1 and 4 mo. However, the length of the colonies increased from 0.73 to 5.78 mm between 1 and 4 mo. These experimen ts establish the feasibility of studying in a systematic and quantitative m anner the pattern and kinetics of the colonization process. Using spermatog onial transplantation as a functional assay, it should be possible to asses s the effects of various treatments on stem cells and on recipient seminife rous tubules to provide unique insight into the process of spermatogenesis.