The molecular anatomy of mouse skin during hair growth and rest

Abstract

HIGHLIGHTS--Comprehensive single--cell transcriptome atlas of full--thickness skin --Outer root sheath (ORS) is composed of two distinct cell types --Companion layer transcriptionally resembles ORS --Transcriptional reconstruction of the internal hair follicle (HF) lineages --Molecular identification of an asymmetric HF--bulb structure --Spatial map of fibroblast subtypes in the skin --Online tool. http://kasperlab.org/tools 2 SUMMARYSkin homeostasis is orchestrated by dozens of cell types that together direct stem cell renewal, lineage commitment and differentiation. However, a systematic molecular atlas of full--thickness skin is lacking. Here, we used single--cell RNA--sequencing and mRNA--FISH to determine gene-expression identity and spatial location of skin cells during hair growth and rest. We defined 55 cell populations and made striking discoveries about the outer root sheath (ORS) and inner hair follicle layers that together coordinate hair production. The ORS is composed of two distinct cell types, companion layer cells resemble ORS and not inner layer cells, and we identified an asymmetric inner--layer structure with ORS cell identity. Moreover, the inner layers branch from transcriptionally uncommitted progenitors, and each lineage differentiation passes through an intermediate state. Altogether, we generated a comprehensive atlas with molecular and spatial information on epithelial and stromal cells, including fibroblasts, vascular and immune cells, that will spur new discoveries in skin biology.3

Dicer- and BSC-dependent miRNAs during murine anagen development

“…The cellular decrease in DICER throughout mutant HFs was likely due to HF resolve to monoclonality as also shown by the K15PR1Cre+:R26R-Confetti reporter line ( Figure 2H ). Furthermore, the DICER immunostaining pattern in the control animals was consistent with recently available single cell-RNAseq data showing Dicer mRNA expression specifically within a subset of Cx/IRS as well as ORS cells within anagen HFs (Joost S, 2019) ( Figure 2I ), suggesting the cell types of miRNA dependency. Previous findings have underscored the role of miRNAs during skin development and post-natal skin maintenance by manipulating specific cell types.…”

“…To test our hypothesis, we performed hair depilation assays during the resting stage of the HF growth cycle (P50) using inducible Tarbp2 and Dicer floxed mouse lines crossed to keratin 15 (K15) PR1Cre transgenic mice ( Figure 1A ). This system dominantly ablates Tarbp2 and Dicer within outer BSCs upon RU486 treatment and not within cycling and basal interfollicular epidermal cells as previously performed (Joost S, 2019, Teta et al, 2012). By visual inspection, both control Tarbp2 +/+ :K15PR1Cre+ and experimental Tarbp2 flox/flox :K15PR1Cre+ mice exhibited hyperpigmentation at 9 days post depilation (DPD) ( Figure 1B ).…”

“…ANA cells consist of outer layer (OL) cells, germinative layer (GL) cells, inner root sheath (IRS) cells, cortex/cuticle (CX) cells, and medulla (MED) cells. Data derived from: (Joost S, 2019)…”

“…Only a few studies have investigated the role of miRNAs during the post-natal period within skin cells. For example, Dicer within keratin 5 (K5)-positive epithelial keratinocytes and/or HF epithelial stem cells (Joost S, 2019) of young mice was found to be required for post-natal HF growth and plucking-induced anagen development associated with strong phenotypes (Teta et al, 2012). Recently, miR-218-5p was shown to regulate post-natal skin and HF development by induction of the Wnt signaling pathway (Zhao et al, 2019), however the exact cell types involved remain unclear.…”

Dicer- and Bulge Stem Cell-Dependent MicroRNAs During Induced Anagen Hair Follicle Development

“…Only a few studies have investigated the role of miRNAs during the post-natal period within skin cells. For example, Dicer and Drosha within keratin 5 (K5)-positive epithelial keratinocytes and/or hair follicle medulla and epithelial stem cells (Joost et al, 2020) of young mice were found to be required for post-natal hair follicle growth and plucking-induced anagen development (Teta et al, 2012). Recently, miR-218-5p was shown to regulate post-natal skin and hair follicle development by induction of the Wnt signaling pathway (Zhao et al, 2019), however, the exact cell types involved remain unclear.…”