Process of platelet production from mature megakaryocytes through the differentiation of stem cells has complex and unique stages. The present study provides a novel assay system to quantitatively assess the levels of (A) megakaryocyte maturation from hematopoietic stem cells and (B) proplatelet formation from mature megakaryocytes under live culture conditions for extended periods of time. See Figure 2 in the article by Thon et al that begins on page 1975. Professional illustration by Marie Dauenheimer.