GATA1 is a master transcription factor of megakaryopoiesis and erythropoiesis, and loss-of-function mutation can induce accumulation of megakaryocyte-erythroid progenitors (MEPs) in mice and humans. Accordingly, the murine MEP cell line (termed GIME2 cells) encoding doxycycline (dox)-inducible anti-Gatal shRNA on Hprt locus has been developed. The cells were CD41(+)CD71(+)KIT(+), expand under dox, stem cell factor, and thrombopoietin (TPO), and terminally differentiate into erythroid cells or megakaryocytes upon removal of dox. Surprisingly, in this study, these Gata1(low) murine MEPs displayed accelerated growth from around 90-100 days after cell culture, impeded megakaryocytic potential, and maintained erythropoiesis. We specified them as late GIME2 cells and discovered that increased CD41(+) KIT+ population during long-term culture was the main reason for the delayed megakaryopoiesis. The CD41 expression level was partially de-repressed by PI3K/AKT inhibitors, suggesting that TPO-mediated cell survival signaling pathway might have impacted on CD41 in the late GIME2 cells. Nevertheless, among the late cells, the CD41(+)KIT(+) cells could still generate megakaryocytes on dox withdrawal. Taken together, GIME2 cells could provide a good model to study molecular mechanism of hematopoiesis because of their ability to expand excessively without artificial immortalization. (C) 2020 Elsevier Inc. All rights reserved.