HOXA9 is part of the A cluster on chromosome 7 and encodes a DNA-binding transcription factor which may regulate gene expression, morphogenesis, and differentiation. HOXA9 is highly similar to the abdominal-B (Abd-B) gene of Drosophila. A specific translocation event which causes a fusion between HOXA9 and the NUP98 gene has been associated with myeloid leukemogenesis. Read-through transcription exists between HOXA9 and the upstream homeobox A10 (HOXA10) gene. In vertebrates, the genes encoding the class of transcription factors called homeobox genes are found in clusters named A, B, C, and D on four separate chromosomes. Expression of these proteins is spatially and temporally regulated during embryonic development.