*2.2.1.1. Mouse cell lines*

The most widely used immortalized mouse erythroid cell lines are MEL cells, which are EBLs transformed by Friend Leukemia virus. The viral gp55 protein activates the Epor to sustain cell growth, whereas integration of the virus upstream of *PU.1* or Friend leukemia integration 1 (*Fli-1*) induces constitutive high expression and inhibits differentiation. Leukemogenesis and the establishment of cell lines require additional inactivation of tumor suppressor protein p53 [100]. Under conditions that enable transient expansion of primary mouse cultures (serum-free medium supplemented with Epo, SCF, and glucocorticoids), lack of p53 is sufficient to establish immortalized cell lines with full differentiation potential in the absence of SCF and glucocorticoids [13].
