Four murine monoclonal antibodies specific for the inner root sheath in the human hair follicle
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Keywords:
Stratum granulosum
Epidermis (zoology)
Inner root sheath
Stratified squamous epithelium
Immunofluorescence
Human skin
Objective
To evaluate the expression patterns of common hair follicle keratins in the hair follicle stages.
Methods
The mouse skins at different hair follicle stages including hair follicle morphogenesis, anagen onset, anagen, catagen, and telogen were harvested and embedded in paraffin. The sections were stained with anti-Krt5, anti-Krt6, anti-Krt10, anti-Krt14, anti-Krt15, and anti-Krt19 by immunostaining.
Results
Krt5 was expressed in the hair follicle epithelial of telogen and anagen stages. Krt6 was expressed in the outer root sheath and inner root sheath cells of hair follicles in all stages. Krt10 was expressed in the matrix and inner root sheath of anagen and catagen stages. Krt14 was expressed in the hair follicle epithelial of anagen and telogen stages. Krt15 and Krt19 were expressed in the bulge cells of morphogenesis, anagen onset, and telogen stages.
Conclusion
The keratins can only be used as hair structure or hair follicle stem cell markers at specific hair follicle stages. Researchers should determine the expression pattern of the hair follicle keratins in all hair follicle stages before using them as potential markers.
Key words:
Keratins; Hair follicle; Hair cycle; Immunofluorescence
Inner root sheath
Hair cycle
Immunostaining
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Stratum granulosum
Epidermis (zoology)
Inner root sheath
Stratified squamous epithelium
Immunofluorescence
Human skin
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The hair follicle is a skin micro-organ specific to mammals and responsible for the formation of the hair. During postnatal life, the hair follicle undergoes recurrent phases of growth (anagen), regression (catagen) and rest (telogen) termed the hair cycle. The cellular and molecular mechanisms that regulate the hair cycle recapitulate some of the events occurring during morphogenesis. Despite significant advances in the understanding of biology of the hair follicle, the mechanisms regulating the switch from anagen to catagen remain mysterious. Fgf5, a member of the fibroblast growth factor family, has been proposed as a key regulator of the transition between anagen and catagen. Mice that do not produce active Fgf5 have an angora (go/go) phenotype characterized by an extended anagen phase and long hairs. Nevertheless, Fgf5 null hair follicles still enter catagen, suggesting that other mechanisms contribute to the control of the hair cycle. Previous work in the laboratory using Fgf5Lacz/LacZ null mice has unraveled a close connection between the onset of catagen and the diameter of the hair. Using the whisker follicle as a model system, we have confirmed these results and demonstrated by in situ hybridization that the expression of the Fgf5 gene is switched-on in the supra-bulbar region of the outer root sheath, progressively extends towards the lower extremity of the outer root sheath and is switched-off in the supra-bulbar region of the outer root sheath several days before the onset of catagen. We have also demonstrated that the number of cell layers in the hair cortex progressively increases with time to reach the exact same number a few days before the end of anagen in both wild-type and Fgf5 null follicles confirming our working hypothesis that Fgf5 does not directly trigger catagen. Next, we have demonstrated for the first time that the basal cortex-forming cells could divide symmetrically. These rare symmetrical divisions result in the formation of additional cell layers in the cortex. These results support our working hypothesis that a complex regulatory loop involving the outer sheath, the dermal papilla (that express Fgfr1, the Fgf5 receptor), the cortical matrix and the supra bulbar region is critical in controlling whisker growth. We have then demonstrated by q-RTPCR and immunostaining that several mechanosensitive channels are specifically expressed in the regions of interest. Moreover, several genes important for signaling are also expressed in these regions. Altogether, our results support the provocative hypothesis that the progressive increase in the width of the hair induces a mechanical pressure that leads to the activation of mechanosensitive channels, which in turn activate specific signaling pathways and ultimately result in the control of the expression of the Fgf5 gene in the supra-bulbar region of the outer root sheath and then in the control of the hair cycle.
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AbstractWe have examined the expression of the Hoxa4 gene in embryonic vibrissae and developing and cycling postnatal pelage hair follicles bydigoxigenin-based in situ hybridization. Hoxa4 expression is first seen in E13.5 vibrissae throughout the follicle placode. From E15.5 toE18.5 its expression is restricted to Henle’s layer of the inner root sheath. Postnatally, Hoxa4 expression is observed at all stages ofdeveloping pelage follicles, from P0 to P4. Sites of expression include both inner and outer root sheaths, matrix cells, and the interfollicularepidermis. Hoxa4 is not expressed in hair follicles after P4. Hoxb4, however, is expressed both in developing follicles at P2 and in catagen atP19, suggesting differential expression of these two paralogous genes in the hair follicle cycle. q 2000 Elsevier Science Ireland Ltd. Allrights reserved. Keywords: Hoxa4; Hoxb4; Hox genes; Hair follicle; Outer root sheath; Henle’s layer; Inner root sheath; Matrix; Dermal papilla; Skin; In situ hybridization
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Trichilemmal keratinization, first described in Maurer in 1895 and rediscovered by Holmes (1968) and Pinkus (1968) converts the stratified epithelium of the outer root sheath into anuclear keratin without an intervening keratohyalin layer. It is a distinct seventh type of keratinization in the hair follicle, not derived from the hair matrix. It occurs wherever outer root sheath is not apposed to inner root sheath, in anagen in the zone of sloughing just below the opening of the sebaceous duct, in catagen in the trichilemmal sac surrounding the lower end of the dying hair shaft where it forms the club of the telogen hair. Electron microscopic study of the thick hairs of dogs (but not the tiny hairs of rodents) reveals intricate infoldings of non-keratinized and keratinized cells. It also shows unique ladder-like membrane coating granules in anagen, which are strongly acid phosphatase-positive and are suggested to be the source of enzyme involved with disintegration of the inner root sheath.
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Hair cycle
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Hair follicle growth cycle proceeds through a series of stages in which strict control of cell proliferation, differentiation, and cell death occurs. Transgenic mice expressing human papillomavirus type 16 E6/E7 papillomavirus oncogenes in the outer root sheath (ORS) display a fur phenotype characterized by lower hair density and the ability to regenerate hair much faster than wild-type mice. Regenerating hair follicles of transgenic mice show a longer growth phase (anagen), and although bulb regression (catagen) occurs, rest at telogen was not observed. No abnormalities were detected during the first cycle of hair follicle growth, but by the second cycle, initiation of catagen was delayed, and rest at telogen was again not attained, even in the presence of estradiol, a telogen resting signal. In conclusion, expression of E6/E7 in the ORS delays entrance to catagen and makes cells of the ORS insensitive to telogen resting signals bearing to a continuous hair follicle cycling in transgenic mice.
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