Figure 4: The SSEA-4 positive but not the SSEA-4 negative cells of human testis form colonies in long-term culture. (A-F): The SSEA-4(+) cells freshly isolated from human testes (A), and in culture after 6 days (B & C) and 30 days (D). Grape-shaped colonies (shown by arrows), characteristic of SSCs, were observed after the first 6 days of culture. However, those initial colonies also contained cells that later (after the first month of culture) became adherent and acquired a fibroblast-like morphology. Therefore, to demonstrate the increase in stem cell numbers, the 30-day-old culture (D) should be compared with the later stages (E & F). Four months after the initiation of culture, the morphology of the colonies did not change (E & F). (G & H): The SSEA-4 negative cells consisted exclusively of myofibroblasts, devoid of colonies.