The HOXB3 gene is transcribed to yield mRNA (in embryos in Giampaolo et al. 1989, in carcinoma cells in Simeone et al. 1990). The HOXB3 mRNA is a target of the microRNAs miR-7 and miR-218 in breast cancer cells (Li et al. 2012) and miR-10A (Weiss et al. 2009). In mouse embryos Hoxb3 mRNA is observed strongly in rhombomere 5 and more weakly in rhombomeres 6 and 7 of the hindbrain. Hoxb3 mRNA is also observed in mesodermal derivatives including lung, stomach, pancreas, and metanephros, and in neural crest derivatives.