c-Myc expression in human anagen hair follicles

Abstract

The hair follicle represents a very attractive organ system for studying the precise balance between cell proliferation, growth, differentiation, and death of cells, because it periodically and regularly regenerates, retaining its morphogenetic signals throughout its life. One of the most intriguing oncogenes which is able to induce both cell growth and apoptosis, depending upon the environmental conditions, is c-myc. The aim of the present study was to investigate its presence and localization in human hair follicles by immunohistochemistry and immunofluorescence. Our observations demonstrated the consistent presence of two clusters of cMyc-expressing cells in anagen follicles, located in two annular regions of the inner root sheath, at the border between cells characterized by putative trichohyalin granules and cells which are keratinized. The lower group belongs to Henle's layer, while the upper group belongs to Huxley's layer. cMyc oncoprotein seems to favour apoptosis/differentiation and may be a marker for terminal differentiation of trichocytes, at least in the inner root sheath. Our findings agree with the interpretation that the complex morphology of the hair follicle reflects its complex function; the extrusion of a highly organized multicellular structure, the hair shaft, driven by another highly organized multicellular structure, the inner root sheath.

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

“…As outlined previously for c‐Myc, 4 a correlation between the immunostaining for Max and Bin1 and changes in the morphological features of cells of the IRS was clearly observed. In the regions where Max and Bin1 immunostaining reached the levels of the c‐Myc‐positive rings there was a rather abrupt disappearance of putative trichohyalin granules (Fig.…”

“…In a previous investigation, we demonstrated the presence of two c‐Myc‐positive rings of keratinocytes located, respectively, in the regions of the IRS where Henle’s and Huxley’s layer cells undergo clear morphological modification typical of their terminal differentiation phase. Because of their position with respect to the axes of the HF, the rings were denoted lower ring (LR, in Henle’s layer) and upper ring (UR, in Huxley’s layer) 4 …”

“…We have recently shown the presence of c‐Myc immunoreactivity in the layers of Henle and Huxley of the inner root sheath (IRS), in two distinct zones of the lower transient portion of the follicle, corresponding to the level where trichohyalin granules disappear and cells acquire the morphological features of keratinized elements 4 . The expression of c‐Myc is classically linked to proliferative events or to apoptotic phenomena, whereas cellular differentiation is usually accompanied by c‐Myc downregulation 5–7 .…”

Diseases of cutaneous appendages

“…Seasonal factors, including temperature and light intensity, play some role in precipitating molting in certain animals. 711,712 A reduction in bcl-2 expression also occurs during catagen. 701 Recent studies have addressed this issue of the 'hair cycle clock'.…”

Evidence that Myc activation depletes the epidermal stem cell compartment by modulating adhesive interactions with the local microenvironment

“…In interfollicular epidermis it is confined to the basal layer, where the proliferating keratinocytes, including the stem cells, reside (Hurlin et al, 1995;Gandarillas and Watt, 1997;Bull et al, 2001). It is highly expressed in the stem cells of the hair follicle, which lie in a region known as the bulge (Bull et al, 2001), and is also expressed in keratinocytes undergoing commitment to hair shaft and inner root sheath differentiation (Rumio et al, 2000;Bull et al, 2001).…”