Pattern of expression of c-Myc, Max and Bin1 in human anagen hair follicles

Background We recently reported the presence of c-Myc immunoreactivity in t wo distinct regions of the inner root sheath (IRS) of human anagen hair fol licles; they corresponded to the regions where keratinocytes of Henle's and Huxley's layers enter the terminal differentiation phase that will lead to their exfoliation in the pilary canal. These regions were denoted lower (L R) ring and upper ring (UR). Objectives To extend these observations to other genes connected to c-Myc a nd specifically to Max and Bin1. Max is the best known heterodimeric partne r of c-Myc, interacting with its C-terminal domain, and Bin1 is an adaptor protein interacting with its N-terminal domain. Methods Human anagen hair follicles were processed for c-Myc, Max and Bin1 immunohistochemistry and immunofluorescence. The presence of different isof orms of Bin1 was evaluated by Western blot analysis. Results Analysis of sections cut in several planes, including tangential, d emonstrated the presence of a third ring of c-Myc-positive cells (intermedi ate ring; IR) in the cuticle of the IRS corresponding to the region where t his thin layer undergoes keratinization. Max immunoreactivity was observed in the three layers of the IRS starting in the lower bulbar region and endi ng in each of them at the level of the corresponding c-Myc-positive ring. B in1 immunoreactivity was clearly distinguished only in Huxley's layer and i n the cuticle, starting in some cells below the UR and terminating at the l evel of the latter. The companion layer of the outer root sheath was also l abelled up to the infundibular region. Max and Bin1 immunostaining were les s consistently observed in other skin adnexae and in the epidermis. Conclusions The results indicate that the asynchronous differentiation alon g the axis of the hair follicle of the different layers of the IRS and of t he companion layer involves the expression of different genes that are inte rrelated in the so-called 'Myc network'. The specific localization of c-Myc in the IRS only at the level of the discrete and limited regions of the th ree rings appears to be the hallmark of the switch from differentiation to terminal differentiation/cell deletion.