869 The specification of Merkel cell in the back skin and glabrous paw skin is controlled by FGFR2-meditated signaling

Abstract

Merkel cells are mechanosensory cells responsible for light touch sensations. In murine hairy skin, Merkel cells are located in touch domes in back skin and in whisker pads. Merkel cells are also present in the glabrous paw skin. While it has been shown that Merkel cells are of epidermal lineage, their progenitor and the regulators that are critical for their specification have not been extensively study. Here, we show that during embryogenesis, SOX9 positive (+) cells located in hair placodes, which were previously known to give rise to hair follicle stem cells, also give rise to Merkel cells in the back skin. In contrast, in the glabrous paw skin, SOX9(+) cells do not give rise to Merkel cells suggesting that hairy and glabrous skins have different Merkel cell precursor populations. We performed RNA-seq transcriptional profiling of Merkel cells on the back and glabrous paw skin and showed that their transcriptomes are similar suggesting that their formation is controlled by similar regulators. Among these regulators is FGFR2-mediated signaling that is essential for Merkel cell formation in both the back skin and glabrous paw skin. Taken together, our results demonstrate that although the precursor cells of Merkel cells in the murine back skin and glabrous paw skin might differ, their formation is controlled by a common genetic program and that FGFR2 plays a critical role in this process.