Geminin-deficient mice showed that Geminin is essential for development [19,20] as it acts as a central regulator in governing cellular differentiation and proliferation of embryonic stem (ES) and embryonic carcinoma (EC) cells [21] as well as in supporting hematopoietic stem cell (HSC) activity and mature blood cell production [12,13,14,18,22,23]. The gene discussed is GMNN; the disease is embryonal carcinoma.