After activation by retinoic acid, the HOXA1 gene is transcribed to yield mRNA (inferred from mouse embryos, also demonstrated in human cancer cells, Chariot et al. 1995, Xu et al. 2014). The mRNA is a target of the microRNAs miR-10a in megakaryocytes (Garzon et al. 2006), miR210 in tumors (Huang et al. 2009), let-7c in non-small cell lung cancer cells (Zhan et al. 2013), miR-99 in epithelial cells (Chen et al. 2013), and miR-100 in tumor cells (Chen et al. 2014), however it is unknown if these play a role in embryogenesis. Opposite strand intergenic transcripts are also observed in adult tissues and placenta (Sessa et al. 2007).
In mouse embryos, expression of Hoxa1 occurs in the neural tube, adjacent mesenchyme, paraxial mesoderm, somites, and gut epithelium from rhombomere 4 to the caudal-most region of the embryo. (Rhombomeres are transiently formed segments in the neural tube that will eventually form the hindbrain.)