ESR1 and Decreased total leukocyte count: Moreover, the use of the estrogen receptor-Hoxb8 fusion system to conditionally immortalize GMPs from TazKO♂ and wt mouse E14-E16 fetal livers [21] revealed that null myeloid progenitor development was largely unaffected; however, the transplantation of null fetal liver cells caused mild and consistent leukopenia.