Polycomb-Mediated Repression and Sonic Hedgehog Signaling Regulate Merkel Cell Specification

The study from April 30, 2016, investigated the molecular mechanisms controlling the development of Merkel cells, which are touch-receptor cells located in touch-sensitive areas of the skin. The researchers found that Sonic hedgehog (Shh) signaling, initiated by the production of Shh ligand in developing hair placodes, is required in the epidermis for Merkel cell specification. They also discovered that the loss of Polycomb repressive complex 2 (PRC2) in the epidermis results in ectopic Merkel cells associated with all hair types. This loss does not alter the inductive signals that specify Merkel cells but expands the field of cells competent to produce Merkel cells through upregulation of key Merkel-differentiation genes, which are known PRC2 targets. However, Merkel cell specification can only occur around hair follicles, which provide necessary Shh signaling. This study highlighted the interplay between epigenetic repression and signaling pathways in regulating fate specification.