Inducible Deletion of Dicer or Drosha Reveals Multiple Functions for miRNAs in Postnatal Epidermis and Hair Follicles

The study investigated the role of miRNAs in adult skin by inducing the deletion of Dicer and Drosha, two key enzymes in miRNA biogenesis, in mice. The findings revealed that both enzymes were crucial for miRNA production, as their deletion resulted in similar phenotypes, indicating their primary role in miRNA biogenesis rather than non-miRNA functions. While neither enzyme was necessary for maintaining resting hair follicles, they were essential during specific phases of hair follicle growth, including the viability of the transient amplifying population, normal hair shaft formation, and the initiation of hair follicle regression. Prolonged loss of either enzyme led to follicular degradation, epidermal thickening, and dermal inflammation, suggesting additional roles for miRNAs in hair follicle maintenance and epidermal homeostasis. The study also identified increased levels of Zeb2 and E2F1 in Dicer mutant skin, implicating these factors in the observed phenotypes and highlighting the importance of miRNAs in hair follicle growth and regeneration.