LAUSR

Insulin‐like growth factor 1 (Igf1) is important for skin development and homoeostasis. However, overexpression and inactivation studies have produced variable findings regarding its role in hair follicle (HF) biology. Here, we studied a conditional and inducible knockout of the Igf1 receptor (Igf1r) in keratin 15‐expressing bulge cells. Deletion of Igf1r after the development of the skin appendages in K15‐Igf1rKO mice showed no abnormalities in epidermal homoeostasis. Numbers of bulge cells were lower in K15‐Igf1rKO mice than in controls, without consequences on wound healing, at least in young mice. K15‐Igf1rKO HFs entered anagen phase earlier than controls and showed a delay in the anagen/catagen switch. The expression of Bmp‐4 mRNA was inhibited in HFs from K15‐Igf1rKO. MED1 transcription was impaired in the epidermis of K15‐Igf1rKO mice. These findings suggest that Igf1r controls the hair cycle, partly through Bmp‐4 activation.