These LSD1fl/fl mice possess loxP sites flanking exons 5-6 of the lysine (K)-specific demethylase 1A (Kdm1a) gene. LSD1 demethylates histone H3 on Lys4 or Lys9 (H3K4/K9) and represses hematopoietic stem and progenitor cell (HSPC) gene expression during hematopoietic differentiation. Mice that are homozygous for this allele are viable and fertile. When bred to mice that express tissue-specific Cre recombinase, resulting offspring will have exons 5-6 deleted in the cre-expressing tissues. For example, when bred to mice expressing Cre-recombinase in hematopoietic cells (see B6.Cg-Tg(Vav1-cre)A2Kio/J Stock No. 008610), double mutant mice die neonatally of severe anemia. Blood counts and bone marrow cellularity are reduced. Also, hematopoietic stem cells, multipotent progenitors, and myeloid progenitor cell numbers decreased 30-fold.