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 two distinct regions of the inner root sheath (IRS) of human anagen hair follicles; 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 (LR) ring and upper ring (UR).


OBJECTIVE
To extend these observations to other genes connected to c-Myc and specifically to Max and Bin1. Max is the best known heterodimeric partner 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 isoforms of Bin1 was evaluated by Western blot analysis.


RESULTS
Analysis of sections cut in several planes, including tangential, demonstrated the presence of a third ring of c-Myc-positive cells (intermediate ring; IR) in the cuticle of the IRS corresponding to the region where this thin layer undergoes keratinization. Max immunoreactivity was observed in the three layers of the IRS starting in the lower bulbar region and ending in each of them at the level of the corresponding c-Myc-positive ring. Bin1 immunoreactivity was clearly distinguished only in Huxley's layer and in the cuticle, starting in some cells below the UR and terminating at the level of the latter. The companion layer of the outer root sheath was also labelled up to the infundibular region. Max and Bin1 immunostaining were less consistently observed in other skin adnexae and in the epidermis.


CONCLUSIONS
The results indicate that the asynchronous differentiation along the axis of the hair follicle of the different layers of the IRS and of the companion layer involves the expression of different genes that are interrelated 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 three rings appears to be the hallmark of the switch from differentiation to terminal differentiation/cell deletion.
Barajon
I
I
Institute of Human Anatomy, University of Milan, Via Mangiagalli 31, 20133 Milan.
Rumio
C
C
Donetti
E
E
Imberti
A
A
Brivio
M
M
Castano
P
P
D048868:Adaptor Proteins, Signal Transducing; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D018859:Hair Follicle / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D009687:Nuclear Proteins / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D025521:Tumor Suppressor Proteins
D048868:Adaptor Proteins, Signal Transducing; C101410:BIN1 protein, human; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C499330:MAX protein, human; C067850:Myc associated factor X; D009687:Nuclear Proteins; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins