Microphthalmia-associated transcription factor is expressed in projection neurons of the mouse olfactory bulb.

Microphthalmia-associated transcription factor (Mitf) is a key regulator for differentiation of the neural crest-derived melanocytes. Mitf consists of multiple isoforms, including melanocyte-specific Mitf-M and widely expressed Mitf-A and Mitf-H. Mitf mRNAs are also expressed in the brain, although the identity of Mitf-expressing cells remains unknown. We therefore aimed to identify Mitf-expressing cells in the brain. By the immunohistochemical analysis, we detected Mitf-expressing cells only in the olfactory bulb of the C57BL/6 mouse. The Mitf-expressing cells were then identified as projection neurons, mitral cells and tufted cells, both of which receive the signal from the olfactory neurons and transmit the information to the olfactory cortex. Real-time RT-PCR analysis showed the expression level of Mitf-M mRNA was comparable to the expression levels of Mitf-A and Mitf-H mRNAs in the olfactory bulb. We then analyzed Mitf-expressing neurons in the olfactory bulb of the homozygous black-eyed white (Mitf(mi-bw)) mouse that is characterized by the lack of melanocytes. Mitf was expressed in mitral cells and tufted cells in the olfactory bulb of the Mitf(mi-bw) mouse, thereby excluding the contribution of melanocytes to the detected expression of Mitf-M. In conclusion, Mitf, including Mitf-M, is expressed in mitral cells and tufted cells of the olfactory bulb.