Deletion of the highly conserved proline-rich region of HOXB4 induces acute myeloid leukemia (AML) in mice. Multiple sequences alignments of (A) HOX paralog group 4 proteins (reference sequences: HOXA4: gi|133778294, HOXD4: gi|23397672, HOXB4: gi|12007115, HOXC4: gi|11993919). (B) Multiple sequence alignment of HOXB4 proteins from different species: Homo sapiens NP_076920.1, Pan troglodytes XP_001173043.1, Canis lupus XP_003639319, Bos taurus NP_001071582.1, Mus musculus NP_034589.3, Rattus norvegicus XP_573184.1, Gallus gallus NP_990624.1, and Danio rerio NP_571193.1. The different colors correspond to the different amino acid classes. In the bottom box, the dendrogram shows the relationship distances (bar indicates genetic distances). (C) Survival curves of transplanted mice. P values of comparisons to HOXB4-ΔPRD_229-360 are indicated. (D) Histologic examinations of multiple organs infiltrated by leukemic blasts from a representative HOXB4-ΔPRD_229-360 diseased mouse. (E) Immunohistochemical examination of multiple organs infiltrated by leukemic blasts from a representative HOXB4-ΔPRD_229-360 diseased mouse that received a second transplant. H&E, hematoxylin and eosin; MPO, myeloperoxidase.