Fluorescent imaging confirmed that Meis1 expression was detected in all emerging Runx1+ HE in vivo, but also in Runx1− EC in an extended region flanking Runx1+ HE (Fig. 4E and Supplementary Fig. 6), consistent with the idea that HE cells arise from a Meis1-expressing EC precursor in vivo. This evidence concerns the gene MEIS1 and hereditary elliptocytosis.