Probes for INS

An increasing amount of evidence indicates that developmental programs are tightly regulated by the complex interplay between signalingpathways, as well as transcriptional and epigenetic processes. Here, we have uncovered coordination between transcriptional and morphogen cues to specify Merkel cells, poorly understood skin cells that mediate light touch sensations. In murine dorsal skin, Merkel cells are part of touch domes, which are skin structures consisting of specialized keratinocytes, Merkel cells, and afferent neurons, and are located exclusively around primary hair follicles. We show that the developing primary hair follicle functions as a niche required for Merkel cell specification. We find that intraepidermal Sonic hedgehog (Shh) signaling, initiated by the production of Shh ligand in the developing hair follicles, is required forMerkel cell specification. The importance of Shh for Merkel cell formation is further reinforced by the fact that Shh overexpression in embryonic epidermal progenitors leads to ectopic Merkel cells. Interestingly, Shh signaling is common to primary, secondary, and tertiary hair follicles, raising the possibility that there are restrictive mechanisms that regulate Merkel cell specification exclusively around primary hair follicles. Indeed, we find that loss of Polycomb repressive complex 2 (PRC2) in the epidermis results in the formation of ectopic Merkel cells that are associated with all hair types. We show that PRC2 loss expands the field of epidermal cells competent to differentiate into Merkel cells through the upregulation of key Merkel-differentiation genes, which are known PRC2 targets. Importantly, PRC2-mediated repression of the Merkel celldifferentiation program requires inductive Shh signaling to form mature Merkel cells. Our study exemplifies how the interplay between epigenetic and morphogen cues regulates the complex patterning and formation of the mammalian skin structures.

Hedgehog (Hh) pathway inhibitors such as vismodegib are highly effective for treating basal cell carcinoma (BCC); however, residual tumor cells frequently persist and regenerate the primary tumor upon drug discontinuation. Here, we show that BCCs are organized into two molecularly and functionally distinct compartments. Whereas interior Hh+/Notch+ suprabasal cells undergo apoptosis in response to vismodegib, peripheral Hh+++/Notch− basal cells survive throughout treatment. Inhibiting Notch specifically promotes tumor persistence without causing drug resistance, while activating Notch is sufficient to regress already established lesions. Altogether, these findings suggest that the three-dimensional architecture of BCCs establishes a natural hierarchy of drug response in the tumor and that this hierarchy can be overcome, for better or worse, by modulating Notch.

Gut mesenchyme provides key stem cell niche signals such as Wnt ligands, but how these signals are regulated is unclear. Because Hedgehog (Hh) signaling is critical for gut mesenchymal development and tumorigenesis, we investigated Hh-mediated mechanisms by analyzing mice deleted for key negative regulators of Hh signaling, Sufu and/or Spop, in the gut mesenchyme, and demonstrated their dosage-dependent roles. Although these mutants exhibit abnormal mesenchymal cell growth and functionally defective muscle layers, villification is completed with proper mesenchymal clustering, implying a permissive role for Hh signaling. These mesenchymal defects are partially rescued by Gli2 reduction. Consistent with increased epithelial proliferation caused by abnormal Hh activation in development, Sufu reduction promotes intestinal tumorigenesis, whereas Gli2 heterozygosity suppresses it. Our analyses of chromatin and GLI2 binding genomic regions reveal its transcriptional regulation of stem cell niche signals through enhancers, providing mechanistic insight into the intestinal stem cell niche in development and tumorigenesis