This new class of progenitors were termed stress BFU-E and further characterization of these new progenitors showed that in addition to BMP4 and Epo, Stem Cell Factor (SCF) and hypoxia provided the minimum set of factors needed to recapitulate, in vitro, the expansion of stress BFU-E observed in vivo during the recovery from PHZ-induced anemia [38]. Here, KITLG is linked to anemia (phenotype).