The double life of HOXB4

HOXB4 is a homeodomain-containing transcription factor with diverse roles in embryonic development and the regulation of adult stem cells. Intriguingly, this gene can act in opposite ways when expressed by different cells, promoting the proliferation of stem cells whilst activating the apoptotic pathway in some embryonic structures. This review considers the basis for these differences in terms of the molecular biology of HOXB4 and the cells that express it.