Keratogenous Zone Research Articles

The walking dead: sequential nuclear and organelle destruction during hair development.

Transition of hair shaft keratinocytes from actively respiring, nucleated cells to structural cells devoid of nucleus and cytoplasm is key to hair production. This form of cell 'death', or cornification, requires cellular organelle removal to allow the cytoplasm to become packed with keratin filament bundles that further require cross-linking to create a strong hair fibre. Although these processes are well described in epidermal keratinocytes, there is a lack of understanding of such mechanisms, specifically in the hair follicle. To gain insights into cornification mechanisms within the hair follicle and thus improve our understanding of normal hair physiology. Scalp biopsies and hair-pluck samples were obtained from healthy human donors and analysed microscopically after immunohistochemical staining. A focal point of respiratory activity was evident in keratogenous zone cells within the hair shaft, which also exhibited nuclear damage. Nuclear degradation occurred via both caspase-dependent and caspase-independent pathways. Conversely, mitophagy was driven by Bnip3L and restricted to the boundary of the keratogenous zone at Adamson's Fringe. We propose a model of stepwise living-dead transition within the first 1 mm of hair formation, whereby fully functional, nucleated cells first consolidate required functions by degrading nuclear DNA, yet continue to respire and provide the source of reactive oxygen species required for keratin cross-linking. Finally, as the cells become packed with keratin bundles, Bnip3L expression triggers mitophagy to rid the cells of the last remaining 'living' characteristic, thus completing the march from 'living' to 'dead' within the hair follicle.

Hypopigmented onychocytic matricoma as a clinical mimic of onychomatricoma: clinical, intraoperative and histopathologic correlations

Onychocytic matricoma is a newly described matrical tumor of the nail unit that clinically presents with localized thickening of the nail plate and melanonychia and represents a benign acanthoma of onychocytes. Onychocytic matricoma can be classified according to its histopathologic type (acanthotic, papillomatous or keratogenous with retarded maturation) and pigmentation (pigmented, melanocytic or non-pigmented). However, there are no published reports of non-pigmented onychocytic matricoma. We report a case of hypopigmented onychocytic matricoma that presented with a thickened nail plate, xanthonychia and histopathologic features of acanthosis, prekeratogenous zone and keratogenous zone cells forming pseudosquamous eddies, and minimal pigmentation with Fontana staining. We also provide detailed clinical, intraoperative and histopathologic correlations of this rare tumor. Both clinicians and dermatopathologists should be aware that onychocytic matricoma can present with xanthonychia, thickening of the nail plate and mimic an onychomatricoma.

Msx2 and Foxn1 regulate nail homeostasis

Epithelial-mesenchymal interactions underlie the foundation for ectodermal appendage formation. Signal molecules such as BMPs and WNTs mediate crosstalk between the two tissue layers and coordinate both the induction and morphogenesis of ectodermal appendages. Here, we analyzed the function of two BMP downstream transcription factors, Msx2 and Foxn1, in nail differentiation. First, we show that Msx2 function is required during onychocyte (nail cell) terminal differentiation. Second, the Msx2/Foxn1/hair keratin pathway controlling hair differentiation is also conserved during onychocyte differentiation. Finally, the Msx2-/-; Foxn1-/- double-mutant nails exhibit a more severe phenotype than either single mutant including nail bed hyperplasia. Together, our data implicate important functions for Msx2 and Foxn1 in regulating differentiation of the keratogenous zone, proliferation of distal nail matrix cells, and organization of the nail bed.

Adamson′s Fringe, Horatio George Adamson, and Kligman′s experiments and observations on Tinea capitis

Adamson's fringe is located at the upper margin of the keratogenous zone of the hair follicle where the nucleated hair shaft cornifies completely and gets converted to hard anucleated keratin. It marks also the area of complete keratinization of the cuticle and Henle's layer of the inner root sheath and the beginning of the stem of the follicle. In Tinea capitis, dermatophytic infection of the hair shaft is restricted to this zone and the fungi do not penetrate further down the infected hair in the bulb of the follicle. The fungi in Adamson's words form “a fringe of mycelium surrounding the hair shaft and project below the lower margin of the sheath of spores around the root-stem.” Horatio George Adamson (1865--1955), a British dermatologist first described this phenomenon, in 1895, and this article describes Adamson's fringe with a short biography of Adamson and discusses Kligman's experiments and observations on Tinea capitis which validated the observations of Adamson and the concept of Adamson's Fringe and described the pathogenesis in Tinea capitis.

Expression Profiling and Cellular Localization of Genes Associated with the Hair Cycle Induced by Wax Depilation

The hair cycle is a highly regulated process controlled by multiple factors. Systematic analysis of gene expression patterns in each stage of the hair cycle would provide information useful for understanding this complicated process. To identify genes associated with the hair cycle, we used DNA microarray hybridization to analyze sequential gene expression patterns in mouse skin following hair cycle synchronization by wax depilation. Messenger RNA levels in mouse skin at various times after depilation were compared with those prior to depilation (resting phase). According to their expression patterns, upregulated genes were categorized into four groups: early anagen, middle anagen, late anagen/early catagen, and middle/late catagen, and processes that take place in each stage were evaluated. We identified 12 new components that are specifically expressed in the hair follicle, 11 genes in anagen including carbonic anhydrase 6, cytokeratin 12, and matrix metalloproteinase-11 in catagen that were confirmed using in situ hybridization. The strategy used here allowed us to identify unknown genes or process previously not suspected to have a role in hair biology. These analyses will contribute to elucidating the mechanisms of hair cycle regulation and should lead to the identification of novel molecular targets for hair growth and/or depilation agents.

L’onychomatricome, une lésion rare de l’ongle

Onychomatricoma is a rare fibroepithelial lesion of the nail matrix with peculiar clinical and histological features. Clinically, it is characterized by a longitudinal band of yellow thickening of the nail plate with transverse overcurvature and splinter hemorrhages. Nail avulsion exposes a villous tumor of the matrix with filamentous digitations extending into multiple holes of the nail plate. Histologically, a thick keratogenous zone forms a thickened nail plate. The lesion in its proximal portion is characterized by deep epithelial invaginations and by a stroma organized in two layers. The distal zone corresponds to multiple fibroepithelial projections extending into the nail plate. The diagnosis can be difficult in the presence of misleading clinical features or when the specimen is incomplete or examined with an improper orientation. Surgical resection is the recommended treatment.

Expression of hair keratins in the adult nail unit: an immunohistochemical analysis of the onychogenesis in the proximal nail fold, matrix and nail bed.

Recently, the expression profiles of the members of the complex hair keratin family have been determined in the human anagen hair follicle. In contrast, the details of hair keratin expression in the human nail unit are poorly known. In order to fill this gap, we have performed an immunohistochemical study of the adult human nail unit by means of specific antibodies against nine hair keratins of both types (hHa2, hHb2, hHa5, hHb5, hHa1, hHb1, hHb6, hHa4 and hHa8) as well as three epithelial keratins (K5, K17 and K10). Formalin-fixed paraffin sections of adult nails were examined using monoclonal and polyclonal keratin antibodies, respectively. Longitudinal as well as transverse sections were investigated. Our study revealed two types of epithelial tissue compartments in the nail unit. The first comprised the eponychium and hyponychium and the nail bed, which expressed only epithelial keratins. While keratins K5, K17 (basal) and K10 (suprabasal) were found in the orthokeratinizing eponychium and hyponychium, throughout, the nail bed epithelium expressed only K5 and K17. The second type comprised the apical and ventral matrix which exhibited a mixed pattern of epithelial and hair keratin expression. Thus, K5 and K17 were expressed in the entire multilayered basal cell compartment of the apical and ventral matrix; however, in the latter, K5 and K17 also occurred in the lowermost layers of the overlying keratogenous zone. The hair matrix keratin hHb5, but not its type II partner hHa5, was seen in the entire keratogenous zone of the apical and ventral matrix, but was also located in the uppermost cell layers of the basal compartment of the ventral matrix, where it overlapped with K5 and K17. Similar to their sequential expression in the hair follicle cortex, hair keratins hHa1, hHb1, hHb6 and hHa4 were consecutively expressed in the keratogenous zone of both the ventral and, albeit less distinctly, apical matrix, with hHa1 initiating in the lowermost cell layers. The expression of hHa8 in only single cortex cells of the hair follicle was also preserved in cells of the keratogenous zone. In the region of the so-called dorsal matrix, we observed two histologically and histochemically distinct types of epithelia: (i) a dominant type, histologically similar to the eponychium and an associated K5, K17 and K10 keratin pattern which clearly extended into the apical matrix, and (ii) a minor type, histologically resembling the postulated dorsal matrix without a granular layer and a cuticle, and exhibiting extended K5 expression as well as hair keratin expression in superficial cells. The coexpression of hHb5 with K5 and K17 in the uppermost cell layers of the basal compartment and the lowermost layers of the keratogenous zone of the ventral matrix prompts us to designate this region the prekeratogenous zone of the ventral matrix. The two alternating types of histology and keratin expression in the dorsal matrix identify this region as a transitional zone between the eponychium and the apical matrix. Finally, our data clearly show that the ventral matrix is the main source of the nail plate. In addition, the mixed scenario of hair and epithelial keratins, including demonstrable amounts of K10, in superficial cells of the apical matrix, lends support to the notion that the dorsal portion of the nail is generated by the apical matrix.

The RAIG Family Member, GPRC5D, Is Associated with Hard-Keratinized Structures

Retinoic acid-inducible gene-1 was originally identified as an orphan G-protein coupled receptor induced by retinoic acid. Three highly homologous oGPCR (GPRC5B, GPRC5C, and GPRC5D) have since been classified into the RAIG1 family. We describe here, the unique tissue distribution of GPRC5D and its mechanism of expression. Hybridization in situ has shown that GPRC5D is expressed in differentiating cells that produce hard keratin, including cortical cells of the hair shaft, the keratogenous zone of the nail, and in a central region of the filiform papillae of the tongue. The GPRC5D transcript is expressed in hair follicles during mid- and late anagen, and catagen but not at telogen and early anagen phases. The differentiation-inducer, all-trans retinoic acid, induces GPRC5D expression in cultured hair bulb cells. Because the tissue distribution of GPRC5D indicates a relationship with hard keratins that constitute the major structural proteins of hard epithelial tissues, we investigated the effect of GPRC5D on acid hard keratins. Analyses of cultured cells showed that transient overexpression resulted in suppression of Ha3 and stimulation of Ha4 hair keratin gene expression. The expression was maintained in the hair follicles of whn-deficient (nude) mice, suggesting that this gene is regulated by a signal pathway different from that of hair keratin synthesis. Collectively, these data provide a framework for understanding the molecular mechanisms of GPRC5D function in hard keratinization.

Long-range, nonautonomous effects of activated Notch1 on tissue homeostasis in the nail☆

Using an antibody directed against γ-secretase-generated antigen unique to activated Notch1, we mapped Notch1 activation strictly to suprabasal cells in epidermis, nail matrix, and other skin appendages during normal development. The consequences of Notch1 activation in keratinizing nail cells were investigated in a transgenic mouse model. Ectopic activation of Notch1 in postmitotic cells within the nail keratogenous zone resulted in longer nails. BrdU labeling revealed an increased number of mitotic cells in transgenic nails. The matrix and keratogenous zone expanded distally due to the increase in cell numbers. The mitosis-promoting effects by a gene product expressed exclusively in postmitotic cells indicates a long-range effect of transgenic Notch1 on regulation of nail homeostasis. We demonstrate that activation of Notch1 in the keratogenous zone resulted in ectopic activation of Wnt signaling, the first such evidence in vertebrates. However, we detected little or no β-catenin activation in proliferating matrix cells, indicating that Wnt is at most an indirect mediator of Notch-induced proliferation. These data support the existence of a novel, cell-nonautonomous role for Notch in maintaining homeostasis of stratified squamous epithelia by indirectly promoting mitosis in basally located cells.

Gene expression of Sh3d19, a novel adaptor protein with five Src homology 3 domains, in anagen mouse hair follicles

Background: Sh3yl1, which contains one Src homology (SH) 3 domain, has been previously identified from mouse skin and considered to play an important role in hair follicle formation by interacting with other proteins. Objective: We performed this study to identify proteins capable of associating with Sh3yl1. Methods: We screened a mouse skin cDNA library using the SH3 domain of Sh3yl1 as bait in the yeast two-hybrid system. Results: We identified a 420-amino acid-long protein containing a proline-rich stretch and five carboxyl-terminal SH3 domains, which we have termed Sh3d19. We confirmed the interactions between Sh3yl1 and Sh3d19 by in vitro binding assays. Northern blot analysis showed that Sh3d19 transcripts in mouse skin were expressed in accordance with the hair cycle. Furthermore, RNA in situ hybridization studies demonstrated that its transcripts were detected predominantly in the medulla cells at the level corresponding to the keratogenous zone of the hair follicles during the mid and late anagen phases. Conclusion: Sh3d19 is a novel adaptor protein that may be involved in the development of medulla cells during the anagen phase.

Bowen's disease clinically simulating an onychomatricoma

Onychomatricoma (OM) is an uncommon benign tumor clinically characterized by a thickened yellowish nail with transverse over curvature. A pigmented variant has recently been described. Histologically, the diagnosis requires 3 prerequisites: (1) a fibroepithelial tumor consisting of 2 portions: the proximal zone (under the proximal nailfold, characterized by deep epithelial invaginations and a fibrillary and fibrocytic stroma), whereas the distal zone (corresponding to the lunula) presents with multiple digitations along its connective tissue axes; (2) a matricial tumor typified by a thick keratogenous zone; and (3) a thick nail plate, perforated by cavities. We describe a case that appears clinically identical to a pigmented OM, but with histologic malignant patterns. Because histologic features were consistent with Bowen's disease, we ruled out a malignant OM. We report a new variant of Bowen's disease presenting as OM, and this observation underlines the necessity for a histologic assessment of all forms of OM, especially those associated with a pigmented band (a sign sometimes observed in Bowen's disease). (J Am Acad Dermatol 2002;47:947-9.)

Microtubule associated protein (MAP-2) expression defines the companion layer of the anagen hair follicle and an analogous zone in the nail unit.

Microtubule associated protein 2 (MAP-2) is one of a group of polypeptides that are an integral component of the microtubular cytoskeletal structure of the central and peripheral nervous system. During the course of another investigation that utilized immunohistochemistry, MAP-2 expression was observed in the hair follicle, almost exclusively in the innermost layer of the outer root sheath of the anagen follicle. This innermost layer, the so-called companion layer, has unique properties that clearly distinguish it from the rest of the outer root sheath. Among these are diminished glycogenation and an intimate association with the Henle's layer, which it directly apposes. Numerous intercellular connections exist between the companion layer and Henle's layer and, in fact, the companion layer accompanies Henle's layer during its vertical ascent in the follicle. Circumferentially oriented keratin filaments have also been demonstrated between the companion layer and Henle's layer, apparently providing structural support to the inner root sheath. Experimentally, disturbances in the keratin filaments of the companion layer in animals ultimately results in destruction of the hair follicle and an alopecia. Immunohistochemical studies for MAP-2 were performed on 25 additional paraffin-embedded scalp specimens using standard techniques. Because of the parallels between the follicle and nail, MAP-2 expression in the nail unit was also investigated in three specimens. The presence of MAP-2 in the companion layer was confirmed in all cases. Intense MAP-2 expression in the companion layer begins at the B-fringe (the start of the keratogenous zone with cornification of the Henle's layer of the inner sheath) and extends to the level of the isthmus where the inner root sheath exfoliates. MAP-2 is also expressed in the upper layers of the nail matrix. The expression of MAP-2 almost exclusively in the companion layer is probably related to the unique cytoskeletal structure of this microanatomic layer. Since experimental evidence has shown that the cell cytoskeleton is important to the integrity of the hair follicle, it is probable that MAP-2 expression is also important and disturbances in its expression could play a role in the pathogenesis of some alopecias. MAP-2 may play a similar role in the nail matrix.

The onychomatricoma: additional histologic criteria and immunohistochemical study.

Onychomatricoma (OM) is a tumor of the nail matrix typified histologically by multiple distal fibroepithelial projections and a thick keratogenous zone forming multiple V-shaped invaginations at the level of epithelial ridges, with the formation of a thick nail plate. In its proximal portion, the thickness of the nail looks like a spur originating from the ventral part of the nail plate. In its distal part, beyond the lunula, the nail plate is globally thickened and filled with cavities containing serous fluid. Often, however, the pathologist is not provided with the nail plate. The diagnosis then rests on the presence of a fibroepithelial tumor. In this article the histologic criteria of OM without nail plate are refined and OM is characterized immunohistochemically using three tumors fixed in liquid nitrogen and examined separately from the nail plate. On longitudinal section OM without nail plate appears as a unique pedunculated fibroepithelial tumor i.e., the multiple distal epithelial digitations arranged along a transversal plane are not seen. The feature is reminiscent of fibrokeratoma. When OM is visualized in longitudinal section, 3 main criteria differentiate OM from fibrokeratoma: the presence of epithelial-lined invaginations around optical cavities, a stroma organized in 2 layers, and the absence of horny corn. Patterns of expression of cytokeratins and integrins in OM are identical to that observed in the normal nail matrix. Involucrin finds expression from the basal layer through to the top of the epithelium, where it is more marked and where transglutaminase 1 is restricted. Merkel cells detected by CK 20 are increased in number and sometimes disposed in clusters. The fibrous component of OM is composed of 2 layers: a superficial stroma made of numerous fines fibrils of collagen IV intermingled with collagen I, and deep stroma made principally of collagen I. Antibody AE13, specific to trichocytic keratins Ha 1-4, represent a good potential marker of OM. Its V-shaped expression in epithelium ridges offers early identification of the keratogenous zone of OM, on tumors separated from their nail plates and limited to their fibroepithelial components.

A Novel Type II Cytokeratin, mK6irs, is Expressed in the Huxley and Henle Layers of the Mouse Inner Root Sheath

Hair follicle differentiation involves the expression of both epithelial-type keratins or cytokeratins and hair keratins as well as hair keratin-associated proteins. In this study, a cDNA clone encoding a cytokeratin family member was isolated using RNA differential display techniques. The predicted amino acid sequence derived from this clone, revealed a homology with a number of cytokeratins, not only in the central alpha-helical regions but also in the conserved portions of the amino and carboxy terminal domains, indicating that this protein represents a new member of the mouse type II cytokeratin family. Northern blot analysis showed expression in mouse skin, but not in other tissues, including tongue, esophagus, and forestomach. One- and two-dimensional western blot analysis showed that this new cytokeratin was 57 kDa in size and ran slightly below the area of cytokeratin 5, which corresponded to that of the cytokeratin 6 family members. Both RNA in situ hybridization and immunohistochemical studies of mouse anagen hair follicles demonstrated expression of this cytokeratin in the inner root sheath hair cone during anagen III and in the Henle and Huxley layers of the inner root sheath during anagen VI. The expression of the new cytokeratin began in the hair bulb and progressed up to the height of the keratogenous zone. Taken together the sum of the data analyzed, we have termed this novel cytokeratin mK6irs (mouse gene nomenclature k2-6g) to indicate both its similar mobility with K6 in two-dimensional gels and its specific expression in the inner root sheath of the hair follicle.

Human Peptidylarginine Deiminase Type III: Molecular Cloning and Nucleotide Sequence of the cDNA, Properties of the Recombinant Enzyme, and Immunohistochemical Localization in Human Skin

Peptidylarginine deiminase catalyzes the post-translational modification of proteins through the conversion of arginine to citrulline in the presence of calcium ions. In rodents, peptidylarginine deiminase has been classified into four isoforms, types I, II, III, and IV, which are distinct in their molecular weights, substrate specificities, and tissue localization. Of these isoforms, only type III was detected in epidermis and hair follicles. Although the role of this enzyme in these tissues is not yet clear, indirect data have shown that several structural proteins such as filaggrin, trichohyalin, and keratin are substrates for peptidylarginine deiminase. In this study, we cloned the full-length cDNA of human peptidylarginine deiminase type III (3142 bp) from cultured human keratinocytes by reverse transcription-polymerase chain reaction and by rapid amplification of cDNA ends methods. This cDNA contained a 1995 bp open reading frame encoding 664 amino acids (Mr = 74 770). To explore the physicochemical and enzymatic properties of human peptidylarginine deiminase type III, we constructed a plasmid for producing a recombinant human peptidylarginine deiminase type III in bacteria. The enzymatic characteristics of the recombinant enzyme were very similar to those of the rodent peptidylarginine deiminase type III. The recombinant enzyme showed the catalytic activities toward structural proteins of epidermis and hair follicle, filaggrin and trichohyalin, in which the deiminations maxima of about 60% and 13% arginine residues were observed in filaggrin and trichohyalin, respectively. An immunohistochemical study of human scalp skin with a monospecific anti-peptidyl-arginine deiminase type III antibody revealed that the type III enzyme was localized to the inner root sheath and outer root sheath of hair follicles. Peptidylarginine deiminase type III in the inner root sheath was notable between supramatrix and keratogenous zone and was scarcely detected in cornified hair zone. The enzyme was also expressed in the cuticle layer of hair. On the other hand, expression of the enzyme in the epidermis was very low. These data imply that human peptidylarginine deiminase type III is the predominant isoform in hair follicles and may function as a modulator of hair structural proteins, including trichohyalin during hair and hair follicle formation.

μ-Crystallin, Thyroid Hormone-binding Protein, is Expressed Abundantly in the Murine Inner Root Sheath Cells

In an attempt to investigate the genes expressed during the development of mouse hair follicles, we employed RNA differential display and identified a cDNA encoding micro-crystallin, that is a major component of kangaroo lens and a cytosolic NADP-regulated thyroid hormone-binding protein in human kidney. In northern blot study, mu-crystallin transcripts were detected in skin at the highest level among the mouse tissues, whereas lower but detectable in the eye, brain, kidney, heart, lung, and liver. Furthermore, in mouse skin, the gene expression of mu-crystallin followed hair cycle fundamentally, increased significantly during mid- and late anagen phases and decreased during the catagen, telogen, and early anagen phases. In situ hybridization revealed that mu-crystallin gene starts to be activated in hair cone of anagen III, and that in anagen VI, its expression is detected predominantly in the cuticle layer of the inner root sheath from the upper hair bulb to the middle portion of the keratogenous zone and in the Huxley's layer through the keratogenous zone. The expression was not detected in catagen, telogen, and early anagen hair follicles, and any other skin components. These results suggest the possible involvement of mu-crystallin in the development of mouse hair follicles during the anagen phase.

Longitudinal erythronychia with distal subungual keratosis: onychopapilloma of the nail bed and Bowen's disease.

We biopsied longitudinal erythronychia in 16 subjects, and found an onychopapilloma in 14 cases and Bowen's disease in the remaining two. Shared clinical features in addition to erythronychia (or sometimes an interrupted line made up of splinter haemorrhages) were typically a longitudinal marked ridge of the nail bed expanded at the distal nail bed as subungual keratosis, and associated localized onycholysis. The presentation of Bowen's disease in this pattern has not been previously reported. In all cases of onychopapilloma of the nail bed, acanthosis and papillomatosis were evident, and were associated with a keratogenous zone identical to the nail matrix. In addition, we found multinucleate giant cells in two onychopapillomas. We have therefore suggested that the term 'localized, distal, subungual keratosis with multinucleate cells' should be replaced by 'onychopapilloma' (nail-producing papilloma).

The nutritional biochemistry of wool and hair follicles

AbstractThe rôle of various classes of nutrients (energy substrates, vitamins, minerals, amino acids) in the production of wool and hair from follicles, is considered for a variety of animal species. The wool and hair follicle have evolved a number of interesting features of carbohydrate metabolism including glutaminolysis, aerobic glycolysis, significant activity of the pentose phosphate pathway, and storage and mobilisation of glycogen. Presumably the necessity to continue to produce fibre despite fluctuations in the supply of oxygen and nutrients has resulted in some of these unique features, while others reflect the high level of DNA and protein synthesis occurring in the follicle. While it is considered that energy does not normally limit fibre growth, the relative contributions of aerobic and anerobic metabolism will greatly influence the amount of ATP available for follicle activity, such that energy availability may at times alter fibre growth. Alopecia and deficient fibre growth are consistent outcomes of deficiencies of biotin, riboflavin, pyridoxine, folate and pantothenic acid, but the precise rôles of these vitamins in follicle function await elucidation. Folate, in particular appears to play an important rôle in wool production, presumably reflecting its involvement in methionine metabolism. Cholecalciferol (vitamin D) significantly alters fibre growth in cultured follicles; vitamin D receptors are located in the outer root sheath, bulb, and dermal papilla of the follicle; and alopecia occurs in humans with defects in the vitamin D receptor. Retinol (vitamin A), too, appears to influence follicle function by altering keratinocyte proliferation and differentiation, with direct effects on the expression of keratin genes. The receptors for the retinoids are present in the keratogenous zone, the outer root sheath, the bulb, and the sebaceous glands. Vitamin A may also act indirectly on follicle function by influencing the activity of the insulin-like and epidermal growth factors and by altering vitamin D activity. At present there is little evidence implicating alpha-tocopherol (vitamin E) or phytylmenaquinone (vitamin K) in follicular events. Of the minerals, only copper and zinc have been shown to have direct effects on follicle function, independent of effects on food intake. Copper has direct effects on the activity of an unidentified enzyme on oxidation of thiol groups to form disulphide linkages. Wool produced by copper-deficient sheep lacks crimp, is weak and lustrous. Copper is also necessary for the activity of tyrosinase and the tyrosinase-related proteins involved in melanin synthesis. Zinc, like copper, is required for the normal keratinization of fibres but again, the precise rôle has yet to be elucidated. While the importance of amino acid supply for wool growth has long been established, there are still some unaswered questions such as; what are the effects of amino acids on fibre growth in animals other than sheep; what are the characteristics of the amino acid transport genes and proteins operating in the wool and hair follicle; and what are the specific rôles for amino acids in follicle function.

Analysis of Apoptotic Cell Death in Human Hair Follicles In Vivo andIn Vitro

We analyzed changes of growth and apoptotic cell death in human hair follicles. In anagen hair follicles, terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate-biotin nick labeling-positive cells were observed in the keratogenous zone of the upper bulb matrix, the inner root sheath, and the companion layer of the outer root sheath. DNA ladder formation was also detected in anagen hair follicles. In catagen hair follicles, the lower bulb matrix cells around the dermal papilla and the outer layer cells of the outer root sheath became strongly positive, showing that apoptosis in catagen hair is distinct from that in anagen hair. We also confirmed the mRNA expression of four caspases (caspase-1, caspase-3, caspase-4, and caspase-7) in anagen hair follicles by reverse transcriptase-polymerase chain reaction and in situ hybridization. When human anagen hair follicles were cultured in the presence of transforming growth factor-beta or tumor necrosis factor-alpha in the serum-free medium, transforming growth factor-beta but not tumor necrosis factor-alpha induced catagen-like morphologic changes, which were indistinguishable from normal catagen hair follicles. Tumor necrosis factor-alpha, however, strongly inhibited the elongation of the hair shaft in a dose-dependent manner, accompanied by abnormal morphology and increased cell death in the bulb matrix cells. Our results suggest that apoptosis in hair follicles involves two different types. One is related to the terminal differentiation of follicular epithelial cells in anagen hair. The other occurs as a major driving force to eliminate the distinct portion of epithelial components in catagen hair. Furthermore, this study strongly indicates that the transforming growth factor-beta pathway is involved in the induction of catagen phase in human hair cycle.

Gene Expression of Mouse S100A3, a Cysteine-Rich Calcium-Binding Protein, in Developing Hair Follicle

We have previously identified a cysteine-rich calcium binding protein S100A3 present in the cuticle of human hair fiber. In this study, we cloned a cDNA for mouse S100A3, identified its gene location, and elucidated the expression profile throughout hair follicle development. The mouse S100A3 gene was clustered with other S100 family members on chromosome 3, and specifically expressed in dorsal skin containing hair follicles. The level of S100A3 mRNA was elevated during the anagen phase of the hair growth cycle, and sharply declined from the regression phase on. In situ hybridization revealed that the S100A3 gene was prominently expressed in cuticular cells of the hair follicle, and mRNA levels were highest in the keratogenous zone over the entire cuticular layer. Expression was also observed to a lesser extent in differentiated cortical cells; however, expression was not observed in any other component of the hair follicle or dorsal tissues. Immunohistochemical analysis showed that the S100A3 protein accumulated in cuticular and cortical cells undergoing terminal differentiation. These results indicate that the S100A3 gene is exclusively expressed, and the translation product retained, in follicular cells differentiating into major components of the hair shaft. It seems likely that S100A3 plays an important role in calcium-dependent processes leading to hair shaft formation.