Acidic and basic hair/nail ("hard") keratins: their colocalization in upper cortical and cuticle cells of the human hair follicle and their relationship to "soft" keratins

Although numerous hair proteins have been studied biochemically and many have been sequenced, relatively little is known about their in situ distribution and differential expression in the hair follicle. To study this problem, we have prepared several mouse monoclonal antibodies that recognize different classes of human hair proteins. Our AE14 antibody recognizes a group of 10-25K hair proteins which most likely corresponds to the high sulfur proteins, our AE12 and AE13 antibodies define a doublet of 44K/46K proteins which are relatively acidic and correspond to the type I low sulfur keratins, and our previously described AE3 antibody recognizes a triplet of 56K/59K/60K proteins which are relatively basic and correspond to the type II low sulfur keratins. Using these and other immunological probes, we demonstrate the following. The acidic 44K/46K and basic 56-60K hair keratins appear coordinately in upper corticle and cuticle cells. The 10-25K, AE14-reactive antigens are expressed only later in more matured corticle cells that are in the upper elongation zone, but these antigens are absent from cuticle cells. The 10-nm filaments of the inner root sheath cells fail to react with any of our monoclonal antibodies and are therefore immunologically distinguishable from the cortex and cuticle filaments. Nail plate contains 10-20% soft keratins in addition to large amounts of hair keratins; these soft keratins have been identified as the 50K/58K and 48K/56K keratin pairs. Taken together, these results suggest that the precursor cells of hair cortex and nail plate share a major pathway of epithelial differentiation, and that the acidic 44K/46K and basic 56-60K hard keratins represent a co- expressed keratin pair which can serve as a marker for hair/nail-type epithelial differentiation.     

Cyclic hair-loss and regrowth in transgenic mice overexpressing an intermediate filament gene.

We have produced transgenic mice containing up to 250 copies of a sheep wool intermediate filament keratin gene to study the effect of its expression on hair structure and development. Several transgenic lines expressed the gene and in the one containing 250 transgenes, a pattern of hair-loss and regrowth was stably established. Successive waves of hair growth follow periods of denuding like the natural progression of hairs in the mouse hair cycle. By in situ hybridization we have shown that the sheep transgenes are expressed at the correct stage in mouse hair development and at a high level. The transgenic hairs contain not only an elevated level of intermediate filament keratin protein but also a decreased level of the filament-associated proteins. This imbalance disrupts the normal ordered array of these proteins in the cells of the hair cortex and leads to weakened fibres which are prematurely lost.     

Hair follicle differentiation and regulation

Ten years ago, Hardy (1992) wrote a timely review on the major features of hair follicle development and hair growth which she referred to as a secret life. Many of these secrets are now being revealed. The information discussed in this brief review comprises the structure of the hair and hair follicle, the continuing characterisation of the genes for keratin and keratin associated proteins, the determination of the location of their expression in the different cell layers of the hair follicle, molecular signals which control keratin gene expression and post-translational events in the terminal stages of hair formation.     

The catalog of human hair keratins. II. Expression of the six type II members in the hair follicle and the combined catalog of human type I and II keratins.

The human type II hair keratin subfamily consists of six individual members and can be divided into two groups. The group A members hHb1, hHb3, and hHb6 are structurally related, whereas group C members hHb2, hHb4, and hHb5 are rather distinct. Specific antisera against the individual hair keratins were used to establish the two-dimensional catalog of human type II hair keratins. In this catalog, hHb5 showed up as a series of isoelectric variants, well separated from a lower, more acidic, and complex protein streak containing isoelectric variants of hair keratins hHb1, hHb2, hHb3, and hHb6. Both in situ hybridization and immunohistochemistry on anagen hair follicles showed that hHb5 and hHb2 defined early stages of hair differentiation in the matrix (hHb5) and cuticle (hHb5 and hHb2), respectively. Although cuticular differentiation proceeded without the expression of further type II hair keratins, cortex cells simultaneously expressed hHb1, hHb3, and hHb6 at an advanced stage of differentiation. In contrast, hHb4, which is undetectable in hair follicle extracts and sections, could be identified as the largest and most alkaline member of this subfamily in cytoskeletal extracts of dorsal tongue. This hair keratin was localized in the posterior compartment of the tongue filiform papillae. Comparative analysis of type II with the previously published type I hair keratin expression profiles suggested specific, but more likely, random keratin-pairing principles during trichocyte differentiation. Finally, by combining the previously published type I hair keratin catalog with the type II hair keratin catalog and integrating both into the existing catalog of human epithelial keratins, we present a two-dimensional compilation of the presently known human keratins.     

Genetic and biochemical aspects of keratin synthesis by hair follicles

In this review article the data about synthesis and gene regulation of keratin by hair follicles have been summarized. It has been shown that both differentiation of hair follicle matrix cells and normal growth of hair require the coordinated activities of the genes encoding structural proteins. The keratin genes are clustered in families and are usually 5-10 kb in the genome. The separate clusters of two keratin IF gene families and five KAP gene families have been discovered and some of them have been mapped. The close relation between these clusters suggests that the "global" regulatory domains might govern their expression.     

Identification of two novel clusters of ultrahigh-sulfur keratin-associated protein genes on human chromosome 11

We analyzed two novel clusters of keratin-associated protein (KAP) genes on human chromosome 11 (11p15.5 and 11q13.5) in which we identified two known human KRTAP5 genes, KerA (=KRN1) and KerB, and nine novel KRTAP5 family genes. RT-PCR analysis of these KAP genes showed preferential expression in human hair root, suggesting these gene products are required for hair formation. Based on the deduced amino acid sequences, all these KAP proteins were classified into an ultrahigh-sulfur (UHS) type KAP with high cysteine content (> 30 mol%). These KAPs also showed high glycine and serine contents (average 24.30 and 21.13 mol%, respectively), distinguishing from other UHS/HS KAP families located on human chromosomes 17 and 21. Dot-matrix analysis revealed a significant similarity between these two KAP gene clusters. We postulated a mechanism by which these two KAP gene clusters are generated via genomic duplication of a primordial gene cluster followed by genetic modification during evolution.     

小鼠超高硫角蛋白基因启动子的克隆及其表达活性分析

目的筛选在小鼠毛囊中具有高表达活性的内源启动子,为建立小鼠被毛特异表达外源蛋白的转基因技术奠定基础。方法以小鼠基因组为模板,克隆得到超高硫角蛋白基因启动子超高硫角蛋白(UHS),将其分别与pβgal-Basic和pAcGFP1-N1载体连接,构建了重组真核表达载体。采用阳离子脂质体法转染胎鼠组织块,分析其表达活性。结果转染后48 h,在蓝光激发条件下可以检测到绿色荧光蛋白(GFP)在小鼠毛囊区高表达,转染96 h后,表达减弱;此外,转染后48 h,βgal染色结果显示在皮肤块的毛囊区存在蓝色点状区域。结论 UHS启动子在小鼠毛囊中具有表达特异性。     

Genetic and biochemical aspects of the synthesis of keratin by hair follicles

Advances in the area of synthesis and genetic regulation of keratin by the wool-creating structures of the skin, i.e., the hair follicles, is generalized. It is stated that differentiation of the cells of the hair bulb matrix, like normal growth of hair, requires the coordinated action of numerous genes, in particular, the expression of genes associated with synthesis of structural proteins. It is shown that all the keratin genes of the follicle are clustered in families and occupy approximately 5–10 kb in the genome. At the present time certain clusters of two families of IF genes (intermediate hair proteins) along with five families of KAR genes (keratin-associated proteins) have been mapped. The close relations that exist between these clusters give us a basis for claiming that “global” regulator domains are capable of regulating their expression.     

Analysis of structural changes in bleached keratin fibers (black and white human hair) using Raman spectroscopy

To investigate the influence of bleaching treatments on keratin fibers, the structure of cross-sections at various depths of bleached human hair (black and white human hair) was directly analyzed without isolating the cuticle and cortex, using Raman spectroscopy. The S-S band intensity existing from the cuticle region to the center of cortex region of virgin white human hair decreased, while the S-O band intensity at 1040 cm(-1), assigned to cysteic acid, increased by performing the bleaching treatment. Especially, the S-O band intensity of the cuticle region increased remarkably compared with that of the cortex region. Also, the amide III (unordered) band intensity in the cortex region increased, indicating that some of the proteins existing throughout the cortex region changed to the random coil form. Moreover, it has been found that the S-S band intensity existing from the cuticle region to the center of the cortex region of the virgin black human hair decreased remarkably, while the S-O band intensity increased significantly compared with that of the virgin white human hair by performing the bleaching treatment. From these experiments, we concluded that the melanin granules including metal ions act as a decomposition accelerator for the oxidizing agent, thereby leading to a higher level of disulfide (-SS-) group cleavage in the black human hair compared with that of the white human hair.     

Activation of the Notch pathway in the hair cortex leads to aberrant differentiation of the adjacent hair-shaft layers

Little is known about the mechanisms underlying the generation of various cell types in the hair follicle. To investigate the role of the Notch pathway in this process, transgenic mice were generated in which an active form of Notch1 (Notch(DeltaE)) was overexpressed under the control of the mouse hair keratin A1 (MHKA1) promoter. MHKA-Notch(DeltaE) is expressed only in one precursor cell type of the hair follicle, the cortex. Transgenic mice could be easily identified by the phenotypes of curly whiskers and wavy, sheen pelage hair. No effects of activated Notch on proliferation were detected in hair follicles of the transgenic mice. We find that activating Notch signaling in the cortex caused abnormal differentiation of the medulla and the cuticle, two neighboring cell types that did not express activated Notch. We demonstrate that these non-autonomous effects are likely caused by cell-cell interactions between keratinocytes within the hair follicle and that Notch may function in such interactions either by directing the differentiation of follicular cells or assisting cells in interpreting a gradient emanating from the dermal papilla.     

Analysis of structural change in keratin fibers resulting from chemical treatments using Raman spectroscopy

In order to investigate the influence of chemical treatments (reduction, heating, and oxidation) on keratin fibers, the structure of virgin white human hair resulting from a permanent hair straightening process at various depths of cross-sectional samples was directly analyzed without isolating the cuticle and cortex, using Raman spectroscopy. The band shape of the cuticle was different from that of the cortex, and the cuticle had a more amorphous structure, compared with the cortex. The S-S band intensity existing in the hair surface remarkably decreased, while the S-S band intensity in the hair center was not changed by performing the reduction process. In the case of heating the keratin fibers after the reduction process, this tendency was unchanged. On the other hand, the amide III (unordered) band intensity in the cortex region increased, indicating that proteins existing throughout the cortex region caused a change to the random coil form. Moreover, approximately 95% of the disconnected -SS- groups were clearly reconnected by performing the oxidation process after heating (the degree of reconnection of -SS- groups was about 90%, in the case of oxidizing after reduction). From these experiments, we concluded that the heat treatment process in the permanent hair straightening treatment caused the randomization of proteins existing throughout the cortex region, thereby contributing to the acceleration of the reconnection of -SS- groups during the oxidation process.     

Desmoglein 4 is expressed in highly differentiated keratinocytes and trichocytes in human epidermis and hair follicle

Desmosomes are critical for the tissue integrity of stratified epithelia and their appendages. Desmogleins (DSGs) and desmocollins (DSCs) are transmembrane desmosomal cadherins that interact extracellularly to link neighboring epithelial cells. We recently identified a new member of the DSG family, designated desmoglein 4, whose mutations cause hypotrichosis in human, mouse and rat. In this study, we analyzed in detail the expression domains of human desmoglein 4 protein (DSG4) in human skin relative to differentiation markers and other DSGs. Our results show that DSG4 protein is expressed in the more highly differentiated layers of the epidermis. This expression pattern in vivo is recapitulated in highly differentiated HaCaT human keratinocytes and normal human keratinocytes in vitro. In the human hair follicle, DSG4 is expressed specifically in the hair shaft cortex, the lower hair cuticle, and the upper inner root sheath (IRS) cuticle. Using a green fluorescent protein-tagged version of mouse or rat desmoglein 4 protein (Dsg4) and immuno-electron microscopy, we demonstrate that Dsg4 localizes to desmosomes both in vitro and in vivo. The highly specific expression pattern of DSG4 in the human hair follicle, combined with the phenotype of rodent models and human patients with desmoglein 4 mutations, underscores the importance of this adhesion molecule in the integrity of the hair shaft.     

Proteomic tools for the investigation of human hair structural proteins and evidence of weakness sites on hair keratin coil segments

Human hair is principally composed of hair keratins and keratin-associated proteins (KAPs) that form a complex network giving the hair its rigidity and mechanical properties. However, during their growth, hairs are subject to various treatments that can induce irreversible damage. For a better understanding of the human hair protein structures, proteomic mass spectrometry (MS)-based strategies could assist in characterizing numerous isoforms and posttranslational modifications of human hair fiber proteins. However, due to their physicochemical properties, characterization of human hair proteins using classical proteomic approaches is still a challenge. To address this issue, we have used two complementary approaches to analyze proteins from the human hair cortex. The multidimensional protein identification technology (MudPit) approach allowed identifying all keratins and the major KAPs present in the hair as well as posttranslational modifications in keratins such as cysteine trioxidation, lysine, and histidine methylation. Then two-dimensional gel electrophoresis coupled with MS (2-DE gel MS) allowed us to obtain the most complete 2-DE gel pattern of human hair proteins, revealing an unexpected heterogeneity of keratin structures. Analyses of these structures by differential peptide mapping have brought evidence of cleaved species in hair keratins and suggest a preferential breaking zone in α-helical segments.     

Characterization of a cluster of human high/ultrahigh sulfur keratin-associated protein genes embedded in the type I keratin gene domain on chromosome 17q12-21

Low stringency screening of a human P1 artificial chromosome library using a human hair keratin-associated protein (hKAP1.1A) gene probe resulted in the isolation of six P1 artificial chromosome clones. End sequencing and EMBO/GenBank(TM) data base analysis showed these clones to be contained in four previously sequenced human bacterial artificial chromosome clones present on chromosome 17q12-21 and arrayed into two large contigs of 290 and 225 kilobase pairs (kb) in size. A fifth, partially sequenced human bacterial artificial chromosome clone data base sequence overlapped and closed both of these contigs. One end of this 600-kb cluster harbored six gene loci for previously described human type I hair keratin genes. The other end of this cluster contained the human type I cytokeratin K20 and K12 gene loci. The center of the cluster, starting 35 kb downstream of the hHa3-I hair keratin gene, contained 37 genes for high/ultrahigh sulfur hair keratin-associated proteins (KAPs), which could be divided into a total of 7 KAP multigene families based on amino acid homology comparisons with previously identified sheep, mouse, and rabbit KAPs. To date, 26 human KAP cDNA clones have been isolated through screening of an arrayed human scalp cDNA library by means of specific 3'-noncoding region polymerase chain reaction probes derived from the identified KAP gene sequences. This screening also yielded four additional cDNA sequences whose genes were not present on this gene cluster but belonged to specific KAP gene families present on this contig. Hair follicle in situ hybridization data for single members of five different KAP multigene families all showed localization of the respective mRNAs to the upper cortex of the hair shaft.     

Hoxc13在毛囊发育中的作用

Hoxc13属于Hox(Homobox)基因家族Abd-B类成员之一, 与毛囊形成和毛发生长密切相关。毛发结构蛋白KP(角蛋白)和KAP(角蛋白关联蛋白)的表达都受Hoxc13的严格调控, Hoxc13表达水平会直接影响毛发的特性, 对维持毛囊的正常形态也至关重要。文章就Hoxc13的表达水平对毛囊发育和毛发生长的影响及Hoxc13与相关基因的调控进行了综述。     

Localization of low-sulfur keratin proteins in the wool follicle using monoclonal antibodies

Monoclonal antibodies that recognize components of the low-sulfur keratin proteins extracted from Merino wool have been used to locate these components within the wool follicle. Immunoblotting procedures showed that all of the monoclonal antibodies bound more than one of the eight low-sulfur protein components, indicating that these proteins have antigenic determinants in common. Immunofluorescence studies showed that those antibodies specific for the component 7 family of the low-sulfur proteins bound to the developing wool fiber, whereas those antibodies recognizing the component 8 family bound to areas throughout the wool follicle, particularly the inner and outer root sheaths, but also to the fiber, the cuticle, and the epidermis. One of the monoclonal antibodies also bound to intermediate filament networks of cultured human epithelial cells.