Smad1 and Smad5 but Not Smad8 Establish Stem Cell Quiescence Critical for Transforming Premature Hair Follicles During Morphogenesis to the Postnatal State

The document from January 13, 2014, details a study on the importance of Smad1 and Smad5 in hair follicle (HF) development and stem cell quiescence. The researchers found that these proteins are crucial for the proper differentiation of hair follicles and the establishment of a quiescent stem cell population in the HF bulge. Conditional deletion of Smad1 and Smad5 in mice led to neonatal lethality, lack of visible whiskers, and a failure to form a proper hair bulge, resulting in a prolonged anagen phase and disrupted hair cycle. Smad8, while not compensating for the loss of Smad1/5 during morphogenesis, could support hair shaft production postnatally. The study concluded that Smad1 and Smad5 are essential for HF stem cell regulation and the transition of hair follicles to a mature postnatal state, with implications for understanding hair growth and loss. The number of hair follicles analyzed varied, with counts of n = 10, n = 9, n = 20, and n = 15 per HF cycle stage for each sample.