Stabell, A. R. | bioRxiv Science

bioRxiv2019

Single cell transcriptomics of human epidermis reveals basal stem cell transition states

How stem cells give rise to human interfollicular epidermis is unclear despite the crucial role the epidermis plays in barrier and appendage formation. Here we use single cell-RNA sequencing to interrogate basal stem cell heterogeneity of human interfollicular epidermis and find at least four spatially distinct stem cell populations that decorate the top and bottom of rete ridge architecture and hold transitional positions between the basal and suprabasal epidermal layers. Cell-cell communication modeling through co-variance of cognate ligand-receptor pairs indicate that the basal cell populations distinctly serve as critical signaling hubs that maintain epidermal communication. Combining pseudotime, RNA velocity, and cellular entropy analyses point to a hierarchical differentiation lineage supporting multi-stem cell interfollicular epidermal homeostasis models and suggest the \"transitional\" basal stem cells are stable states essential for proper stratification. Finally, alterations in differentially expressed \"transitional\" basal stem cell genes result in severe thinning of human skin equivalents, validating their essential role in epidermal homeostasis and reinforcing the critical nature of basal stem cell heterogeneity.

systems biology↗

bioRxiv2019

Regional Differences Following Partial Salivary Gland Resection

Regenerative medicine aims to repair, replace, or restore function to tissues damaged by aging, disease, or injury. Partial organ resection is not only a common clinical approach in cancer therapy, it is also an experimental injury model used to examine mechanisms of regeneration and repair in organs. We performed a partial resection, or partial sialodenectomy, in the murine submandibular salivary gland (SMG) to establish a model for investigation of repair mechanisms in salivary glands (SGs). After partial sialoadenectomy we performed whole gland measurements over a period of 56 days and found that the gland reached its maximum size 14 days after injury. We used microarray analysis and immunohistochemistry to examine mRNA and protein changes in glands over time. Microarray analysis identified dynamic changes in the transcriptome three days after injury that were largely resolved by day 14. At the 3 day time point, we detected gene signatures for cell cycle regulation, inflammatory/repair response, and extracellular matrix remodeling in the partially resected glands. Using quantitative immunohistochemistry, we identified a transient proliferative response throughout the gland, in which both secretory epithelial and stromal cells expressed Ki67 that was detectable at day 3 and largely resolved by day 14. IHC also revealed that while most of the gland underwent a wound healing response that resolved by day 14, a small region of the gland showed an aberrant sustained fibrotic response characterized by increased levels of ECM deposition and sustained Ki67 levels in stromal cells. The partial submandibular salivary gland resection model provides an opportunity to examine a normal healing response and an aberrant fibrotic response within the same gland to uncover mechanisms that prevent wound healing and regeneration in mammals. Understanding regional differences in the wound healing responses may ultimately impact regenerative therapies for patients.

pathology↗