HOXA5 localization in postnatal and adult mouse brain is suggestive of regulatory roles in postmitotic neurons.

Hoxa5 is a member of the Hox gene family, which plays critical roles in successive steps of the central nervous system formation during embryonic and fetal development. Hoxa5 expression in the adult mouse brain has been reported, suggesting that this gene may be functionally required in the brain after birth. To provide further insight into the Hoxa5 expression pattern and potential functions in the brain, we have characterized its neuroanatomical profile from embryonic stages to adulthood. While most Hox mapping studies have been based solely on transcript analysis, we extended our analysis to HOXA5 protein localization in adulthood using specific antibodies. Our results show that Hoxa5 expression appears in the most caudal part of the hindbrain at fetal stages, where it is maintained until adulthood. In the medulla oblongata and pons, we detected Hoxa5 expression in many precerebellar neurons and in several nuclei implicated in the control of autonomic functions. In these territories, the HOXA5 protein is present solely in neurons, specifically in γ-aminobutyric acid (GABA)ergic, glutamatergic, and catecholaminergic neurons. Finally, we also detected Hoxa5 transcripts, but not the HOXA5 protein, in the thalamus and the cortex, from postnatal stages to adult stages, and in the cerebellum at adulthood. We provide evidence that some larger variants of Hoxa5 transcripts are present in these territories. Our mapping analysis allowed us to build hypotheses regarding HOXA5 functions in the nervous system after birth, such as a potential role in the establishment and refinement/plasticity of precerebellar circuits during postnatal and adult life. J. Comp. Neurol. 525:1155-1175, 2017. © 2016 Wiley Periodicals, Inc.