Since the homozygous loss of mouse L3mbtl3 impairs the maturation of the mouse hematopoietic system to cause anemia and embryonic lethality around E17.5-E19.5 (Arai and Miyazaki, 2005), we employed mouse L3mbtl3tm1a(EUCOMM)Hmgu embryonic stem cells to generate the conditional floxed L3mbtl3fl/fl mice by removing the neo-LacZ elements with the Flp recombinase to establish the loxP sites that flank the exon 5 of the L3mbtl3 allele in the mice (Figure 2—figure supplement 1). This evidence concerns the gene L3MBTL3 and anemia.