BLIMP1 Is Required for Postnatal Epidermal Homeostasis but Does Not Define a Sebaceous Gland Progenitor Under Steady-State Conditions

This study demonstrated that skin fibroblasts in mice originated from two distinct lineages, each contributing differently to skin structure and repair. The upper dermal lineage was crucial for hair follicle formation and included the dermal papilla and arrector pili muscle, while the lower dermal lineage formed the bulk of the extracellular matrix and included reticular fibroblasts and adipocytes. During skin repair, the lower lineage initiated dermal repair, with upper dermal fibroblasts joining later during re-epithelialization. Activation of epidermal β-catenin expanded the upper dermal lineage, allowing hair follicle formation in wounds. These findings provided insights into why wounds typically result in scar tissue without hair follicles and offered a basis for further research into fibroblast lineages in other tissues and their changes with aging and disease.