Nelia Luise Aeckerle

• The aim of this project was to investigate whether primate testicular germ cells could provide a source of pluripotent stem cells (PSC). After removal from their testicular niche, mouse testicular germ line stem cells, called spermatogonial stem cells (SSC), can spontaneously dedifferentiate in vitro to a pluripotent embryonic stem cell (ESC)-like state. The corresponding data on human SSC were not as convincing as for the mouse. Therefore, the aim of this study was to investigate whether PSC could be derived from the common marmoset monkey (Callithrix jacchus) as an experimentally accessible and bio-medically important non-human primate model. Our attempts to generate PSC from cultivated marmoset monkey testicular cells were not successful, although we cultivated the cells according to published protocols for mouse and man. We analyzed pluripotency marker expression in mouse and marmoset SSC. The pluripotency factor LIN28 was strikingly differentially expressed between adult marmoset and mouse testis: in mouse testes LIN28 was present in all spermatogonia, while it was only expressed in a very small subpopulation of monkey and human spermatogonia. This may provide an explanation for the difficulties in the generation of PSC from primate testes. Male neonatal marmoset germ cells are very immature and express many pluripotency-associated genes in situ. We tested their teratoma-formation potential in a heterogeneous population of testicular cells. In the setting of our study, we did not observe any teratoma, but a rearrangement of the injected testicular cells to structures almost indistinguishable from neonatal testicular tissue. For human cells, the derivation of pluripotent embryonic germ cells (EGCs) from primordial germ cells has been shown. Therefore, we investigated the expression of the pluripotency factors OCT4A, NANOG, SALL4, and LIN28 during embryonic and fetal marmoset development. Particularly the expression of OCT4A and NANOG indicates an inherently pluripotent state of marmoset PGCs. Furthermore, we propose a novel model for PGC translocation during embryonic development which challenges the “dogma” of active long-range PGC migration. The data obtained in this project indicate that primate PGCs are the most promising source for the generation of PSC from primate germ cells.