Hair follicles are required for optimal growth during lateral skin expansion

The hair follicles and the interfollicular epidermis of intact mature skin are maintained by distinct stem cell populations. Upon wounding, however, emigration of hair follicle keratinocytes to the interfollicular epidermis plays a role in acute stages of healing. In addition to this repair function, rapidly cycling cells of the upper hair follicle have been observed transiting to the interfollicular epidermis in neonatal skin. Here we report that an absence of hair follicle development leads to shortening and kinking of the mouse tail. These skeletal defects are reduced by stimulating keratinocyte proliferation, suggesting that they arise from impaired epidermal expansion. We confirm that rapidly cycling cells of the hair follicle emigrate to the interfollicular epidermis of the neonatal tail. These results suggest that an absence of hair follicles results in impaired skin growth that is unable to keep pace with the rapidly elongating axial skeleton of the tail. Thus, in addition to their role in wound repair, hair follicles can make a significant contribution to lateral expansion of the interfollicular epidermis in the absence of trauma