Probes for INS

Mammalian epidermis, which is composed of hair follicles, sebaceous glands, and interfollicular epidermis, is maintained by discrete stem cells. In vivo lineage tracing demonstrated that murine LGR5 cells are mainly responsible for hair follicle regeneration whereas LGR6 cells generate sebaceous glands and interfollicular epidermis. However, little is known about their expression in the human skin tumors. In this study, we investigated the expression profile of LGR5 and LGR6 in a variety of human skin tumors including basaloid tumors with follicular differentiation (94 basal cell carcinomas, 18 trichoepitheliomas, 3 basaloid follicular hamartomas, and 12 pilomatricomas) and tumors with ductal differentiation (7 eccrine poromas, 8 hidradenomas, and 5 spiradenomas). LGR5 expression was highest in basal cell carcinomas (BCCs) followed by trichoepitheliomas (TEs) and basaloid follicular hamartomas. LGR6 had the same expression pattern as LGR5, even though its expression was lower. Interestingly, LGR6 expression was detected in stromal cells around the tumor and papillary mesenchymal bodies of TEs but not in stromal cells of BCCs, suggesting different characteristics of tumor-associated fibroblasts between TEs and BCCs. It was unexpected to find that pilomatricomas exclusively expressed LGR6, and its expression was limited to the basaloid cells. Notably, LGR6-positive cells were observed in sweat gland ductal cells in normal skin. This might explain, in part, the finding that LGR6 expression was relatively higher in basaloid tumors with ductal differentiation than in those with follicular differentiation. In particular, spiradenomas displayed the same distribution pattern of LGR6 as normal sweat glands, suggesting the possibility of LGR6-positive cells as tumor stem cells. In conclusion, we documented the different expression patterns of stem cell markers, LGR5 and LGR6 in various skin tumors. These data may provide important insights to understand the origin and development of basaloid skin tumors.

The dynamics and interactions between stem cell pools in the hair follicle (HF), sebaceous gland (SG), and interfollicular epidermis (IFE) of murine skin are still poorly understood. In this study, we used multicolor lineage tracing to mark Lgr6-expressing basal cells in the HF isthmus, SG, and IFE. We show that these Lgr6⁺ cells constitute long-term self-renewing populations within each compartment in adult skin. Quantitative analysis of clonal dynamics revealed that the Lgr6⁺ progenitor cells compete neutrally in the IFE, isthmus, and SG, indicating population asymmetry as the underlying mode of tissue renewal. Transcriptional profiling of Lgr6⁺ and Lgr6⁻ cells did not reveal a distinctLgr6-associated gene expression signature, raising the question of whether Lgr6expression requires extrinsic niche signals. Our results elucidate the interrelation and behavior of Lgr6⁺ populations in the IFE, HF, and SG and suggest population asymmetry as a common mechanism for homeostasis in several epithelial skin compartments.

Despite expanding knowledge regarding the role of astroglia in regulating neuronal function, little is known about regional or functional subgroups of brain astroglia and how they may interact with neurons. We use an astroglia-specific promoter fragment in transgenic mice to identify an anatomically defined subset of adult gray matter astroglia. Using transcriptomic and histological analyses, we generate a combinatorial profile for the in vivo identification and characterization of this astroglia subpopulation. These astroglia are enriched in mouse cortical layer V; express distinct molecular markers, including Norrin and leucine-rich repeat-containing G-protein-coupled receptor 6 (LGR6), with corresponding layer-specific neuronal ligands; are found in the human cortex; and modulate neuronal activity. Astrocytic Norrin appears to regulate dendrites and spines; its loss, as occurring in Norrie disease, contributes to cortical dendritic spine loss. These studies provide evidence that human and rodent astroglia subtypes are regionally and functionally distinct, can regulate local neuronal dendrite and synaptic spine development, and contribute to disease.

The four R-spondin secreted ligands (RSPO1-RSPO4) act via their cognate LGR4, LGR5 and LGR6 receptors to amplify WNT signalling1-3. Here we report an allelic series of recessive RSPO2 mutations in humans that cause tetra-amelia syndrome, which is characterized by lung aplasia and a total absence of the four limbs. Functional studies revealed impaired binding to the LGR4/5/6 receptors and the RNF43 and ZNRF3 transmembrane ligases, and reduced WNT potentiation, which correlated with allele severity. Unexpectedly, however, the triple and ubiquitous knockout of Lgr4, Lgr5 and Lgr6 in mice did not recapitulate the known Rspo2 or Rspo3 loss-of-function phenotypes. Moreover, endogenous depletion or addition of exogenous RSPO2 or RSPO3 in triple-knockout Lgr4/5/6 cells could still affect WNT responsiveness. Instead, we found that the concurrent deletion of rnf43 and znrf3 in Xenopus embryos was sufficient to trigger the outgrowth of supernumerary limbs. Our results establish that RSPO2, without the LGR4/5/6 receptors, serves as a direct antagonistic ligand to RNF43 and ZNRF3, which together constitute a master switch that governs limb specification. These findings have direct implications for regenerative medicine and WNT-associated cancers.