Expression of Maf family proteins in glutamatergic neurons of the mouse olfactory bulb

The fate of neurons in the developing brain is largely determined by the combination of transcription factors they express. In particular, stem cells must follow different transcriptional cascades during differentiation in order to generate neurons with different neurotransmitter properties, such as glutamatergic and GABAergic neurons. In the mouse cerebral cortex, it has been shown that large Maf family proteins, MafA, MafB and c-Maf, regulate the development of specific types of GABAergic interneurons but are not expressed in glutamatergic neurons. In this study, we examined the expression of large Maf family proteins in the developing mouse olfactory bulb by immunohistochemistry and found that the cell populations expressing MafA and MafB are almost identical, and most of them express Tbr2. Since Tbr2 is expressed in glutamatergic neurons in the olfactory bulb, we further examined the expression of glutamatergic and GABAergic neuronal markers in MafA and MafB positive cells. The results showed that in the olfactory bulb, MafA and MafB are expressed exclusively in glutamatergic neurons, but not in GABAergic neurons. We also found that few cells express c-Maf in the olfactory bulb. These results indicate that, unlike the cerebral cortex, MafA and/or MafB may regulate the development of glutamatergic neurons in the developing olfactory bulb. This study advances our knowledge about the development of glutamatergic neurons in the olfactory bub, and also provides insight into the mechanism by which the cortex and olfactory bulb, although both generated from the telencephalon, generate projection and interneurons with different properties.