May 2017 - Vol 137 No 5

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The family of evolutionarily conserved Musashi (Msi) RNA-binding proteins are critical regulators of multiple tissue-specific stem cells. In this issue, Ma and colleagues explore the role of Msi2 in hair follicle (HF) cycling. In double transgenic (DTG) mice with tamoxifen-induced overexpression of Msi2 under control of a keratin 14 (K14) promoter beginning on post-natal day (P) 18, the investigators show that, compared to controls (Ctrl), DTG mice have a delayed entry into anagen after depilation on P21, evident at P30, when only control mice show emerging hair shafts and histologically control HFs are longer. Conversely, in mice expressing a floxed (non-functional) Msi2 gene under the same K14 promoter (cKO), onset of anagen occurs sooner after P21 depilation (shown histologically at P22 and P24 versus control) and HF length at P24 is significantly greater. Further experiments established that Msi2 maintains HF stem cell quiescence by repressing Hedgehog signaling. For details, see the article on page 1015.