Investigating the roles of cellular senescence in embryogenesis and aging

The study explored the dual roles of cellular senescence in aging and embryonic development. In aging, particularly within the epidermal stem cell population, an increase in Keratin-15 positive hair follicle stem cells was observed, but these cells showed reduced functionality and stress tolerance, linked to an imbalance in Jak-Stat signaling rather than direct senescence. This suggested that extrinsic senescence contributes to tissue aging. Conversely, during embryogenesis, senescence was identified as a normal mechanism, crucial for processes like apical ectodermal ridge maintenance, and was dependent on p21. Mice lacking p21 showed defects in embryonic development. The study also found gene-expression similarities between developmental and oncogene-induced senescence, indicating a shared function. Senescence in development involved apoptosis and immune clearance, suggesting it originally evolved as a developmental mechanism before being adapted for adult roles.