Human hair keratins

Noyes-Whitney Dissolution Model-Based pH-Sensitive Slow Release of Paclitaxel (Taxol) from Human Hair-Derived Keratin Microparticle Carriers

This paper describes a convenient and straightforward method developed to extract keratin particles (KPs) from human hair. It also involves their characterization by several methods and encapsulation of the anticancer drug Paclitaxel (Taxol) within them, aiming for targeted delivery to cancerous sites and slow release at their vicinity. The KPs obtained were in micrometer in size. They are capable of encapsulating Taxol within them with a high encapsulation efficiency of 56% and a drug loading capacity of 2.360 g of Taxol per g keratin. As revealed by the SEM elemental analysis, KPs do not contain any toxic metal ion, and hence, they pose no toxicity to human cells. The pH-dependent release kinetics of the drug from KPs indicates that the drug is released faster when the pH of the solution is increased in the 5.0 to 7.0 pH range. The release kinetics obtained is impressive, and once targeted to the cancerous sites, using cancer directing agents, such as folic acid; a glutamate urea ligand known as DUPA; aminopeptidase N, also known as CD13; and FAP-α-targeting agents, the slow release of the drug is expected to destroy only the cancerous cells. The Noyes-Whitney dissolution model was used to analyze the release behavior of Taxol from KPs, which shows excellent fitting with experimental data. The pH dependence of drug release from keratin is also explained using the 3-D structures and keratin stability at different pH values.

In vivo percutaneous permeation of gold nanomaterials in consumer cosmetics: implication in dermal safety assessment of consumer nanoproducts

The increasing emergence of nano-cosmetics in the marketplace provokes safety concerns with respect to percutaneous permeation and toxicity of nanomaterials inside the human body. In this study, in vivo percutaneous permeation and dermal safety of cosmetic cream containing Au nanosheets and extracted Au nanosheets from cosmetic creams are investigated with guinea pigs. Quantitative percutaneous permeation data suggests that Au nanosheets in cosmetic creams permeate into the skin epidermis, dermis, and subcutaneous layer after 10 d cutaneous exposure, but cannot enter the systemic circulation. However, more Au nanosheets are accumulated in the skin and the permeation of Au nanosheets increased after embedded into the cream matrix. Synchrotron radiation X-ray fluorescence (SRXRF) imaging reveals that Au nanosheets in cosmetics penetrate mainly through hair follicles in a time-dependent manner. Cosmetic creams rather than extracted Au nanosheets decrease the cell viability of keratinocytes and slightly induce apoptosis/necrosis of keratinocytes and skin dermal fibroblasts. Intriguingly, the growth of hair is inhibited by the cosmetic cream and the extracted Au nanosheets revealed by HE staining and immunohistochemistry (IHC) assay. Altogether this study provides insights into the comprehensive understanding of percutaneous permeation and dermal safety of cosmetic creams containing Au nanosheets. This work provides reliable methods to study the skin permeation, biodistribution, and dermal safety of nano-cosmetics and reminds the community of the crucial need to combine the assays at molecular, cellular, and organ levels in nanotoxicology research.

Association between maternal exposure to phthalates and lower language ability in offspring derived from hair metabolome analysis

The fetus undergoes a crucial period of neurodevelopment in utero. The maternal hair metabolome provides an integrated record of the metabolic state of the mother prior to, and during pregnancy. We investigated whether variation in the maternal hair metabolome was associated with neurodevelopmental differences across infants. Maternal hair samples and infant neurocognitive assessments (using the Bayley III Scales of Infant Development at 24 months) were obtained for 373 infant-mother dyads between 26–28 weeks’ gestation from the Growing Up in Singapore Towards Healthy Outcomes cohort. The hair metabolome was analysed using gas chromatography-mass spectrometry. Intensity measurements were obtained for 276 compounds. After controlling for maternal education, ethnicity, and infant sex, associations between metabolites and expressive language skills were detected, but not for receptive language, cognitive or motor skills. The results confirm previous research associating higher levels of phthalates with lower language ability. In addition, scores were positively associated with a cluster of compounds, including adipic acid and medium-chain fatty acids. The data support associations between the maternal hair metabolome and neurodevelopmental processes of the fetus. The association between phthalates and lower language ability highlights a modifiable risk factor that warrants further investigation.

Nanoparticle probes for quantifying supramolecular determinants of biosurface affinity

Interactions between macromolecular systems and biosurfaces are complicated by both the complexity of these multivalent interactions and challenges in quantifying affinities. A library of gold nanoparticles (AuNPs) as multivalent probes is used to quantify biosurface affinity, using hair as a model targeted substrate.

Homo- and heteropolymer self-assembly of recombinant trichocytic keratins

In the past two decades, keratin biomaterials have shown impressive results as scaffolds for tissue engineering, wound healing, and nerve regeneration. In addition to its intrinsic biocompatibility, keratin interacts with specific cell receptors eliciting beneficial biochemical cues. However, during extraction from natural sources, such as hair and wool fibers, natural keratins are subject to extensive processing conditions that lead to formation of unwanted by-products. Additionally, natural keratins suffer from limited sequence tunability. Recombinant keratin proteins can overcome these drawbacks while maintaining the desired chemical and physical characteristics of natural keratins. Herein, we present the bacterial expression, purification, and solution characterization of human hair keratins K31 and K81. The obligate heterodimerization of the K31/K81 pair that results in formation of intermediate filaments is maintained in the recombinant proteins. Surprisingly, we have for the first time observed new zero- and one-dimensional nanostructures from homooligomerization of K81 and K31, respectively. Further analysis of the self-assembly mechanism highlights the importance of disulfide crosslinking in keratin self-assembly.

Chemical Forms of Mercury in Human Hair Reveal Sources of Exposure

Humans are contaminated by mercury in different forms from different sources. In practice, contamination by methylmercury from fish consumption is assessed by measuring hair mercury concentration, whereas exposure to elemental and inorganic mercury from other sources is tested by analysis of blood or urine. Here, we show that diverse sources of hair mercury at concentrations as low as 0.5 ppm can be individually identified by specific coordination to C, N, and S ligands with high energy-resolution X-ray absorption spectroscopy. Methylmercury from seafood, ethylmercury used as a bactericide, inorganic mercury from dental amalgams, and exogenously derived atmospheric mercury bind in distinctive intermolecular configurations to hair proteins, as supported by molecular modeling. A mercury spike located by X-ray nanofluorescence on one hair strand could even be dated to removal of a single dental amalgam. Chemical forms of other known or putative toxic metals in human tissues could be identified by this approach with potential broader applications to forensic, energy, and materials science.

Surface active complexes formed between keratin polypeptides and ionic surfactants

Keratins are a group of important proteins in skin and hair and as biomaterials they can provide desirable properties such as strength, biocompatibility, and moisture regaining and retaining. The aim of this work is to develop water-soluble keratin polypeptides from sheep wool and then explore how their surface adsorption behaves with and without surfactants. Successful preparation of keratin samples was demonstrated by identification of the key components from gel electrophoresis and the reproducible production of gram scale samples with and without SDS (sodium dodecylsulphate) during wool fibre dissolution. SDS micelles could reduce the formation of disulphide bonds between keratins during extraction, reducing inter-molecular crosslinking and improving keratin polypeptide solubility. However, Zeta potential measurements of the two polypeptide batches demonstrated almost identical pH dependent surface charge distributions with isoelectric points around pH 3.5, showing complete removal of SDS during purification by dialysis. In spite of different solubility from the two batches of keratin samples prepared, very similar adsorption and aggregation behavior was revealed from surface tension measurements and dynamic light scattering. Mixing of keratin polypeptides with SDS and C₁₂TAB (dodecyltrimethylammonium bromide) led to the formation of keratin-surfactant complexes that were substantially more effective at reducing surface tension than the polypeptides alone, showing great promise in the delivery of keratin polypeptides via the surface active complexes. Neutron reflection measurements revealed the coexistence of surfactant and keratin polypeptides at the interface, thus providing the structural support to the observed surface tension changes associated with the formation of the surface active complexes.

Unusual surface and solution behaviour of keratin polypeptides

Intermediate filament-like aggregation from keratin polypeptides upon increasing [NaCl] as revealed by SANS.

Applications and limitations of lipid nanoparticles in dermal and transdermal drug delivery via the follicular route

Lipid nanoparticles (LN) such as solid lipid nanoparticles (SLN) and nanolipid carriers (NLC) feature several claimed benefits for topical drug therapy including biocompatible ingredients, drug release modification, adhesion to the skin, and film formation with subsequent hydration of the superficial skin layers. However, penetration and permeation into and across deeper skin layers are restricted due to the barrier function of the stratum corneum (SC). As different kinds of nanoparticles provide the potential for penetration into hair follicles (HF) LN are applicable drug delivery systems (DDS) for this route in order to enhance the dermal and transdermal bioavailability of active pharmaceutical ingredients (API). Therefore, this review addresses the HF as application site, published formulations of LN which showed follicular penetration (FP), and characterization methods in order to identify and quantify the accumulation of API delivered by the LN in the HF. Since LN are based on lipids that appear in human sebum which is the predominant medium in HF an increased localization of the colloidal carriers as well as a promoted drug release may be assumed. Therefore, sebum-like lipid material and a size of less or equal 640 nm are appropriate specifications for FP of particulate formulations.

Hair for brain trade-off, a metabolic bypass for encephalization

Hair loss in humans is perplexing and raises many hypothetical explanations. This paper suggests that hair loss in humans is metabolically related to encephalization; and that hair covered hominids would have been unable to evolve large brains because of a dietary restriction of several amino acids which are essential for hair and brain development. We use simulations to imply that hair loss must have preceded increase in brain size & volume. In this respect we see hair loss as a major force in human evolution. We assume that hair reduction required favorable climatic conditions and must have been quick. Using evolutionary and ecological time scales, we pinpoint hair loss to a period around 2.2-2.4 million years ago. The dating is further supported by a rapid selection at that time of the sialic acid deletion mutation which may have protected growing human brains against calcium ion flux. In summary we view encephalization, in part, as a metabolic trade-off between hair and brain. Other biochemical changes may have intervened in the process too; and the deletion mutation of sialic acid hydroxylation may have been involved as well.

Structure-property relationships of meta-kerateine biomaterials derived from human hair

The structure-property relationships of kerateine materials were studied by separating crude hair extracts into two protein sub-fractions, referred to as α- and γ-kerateines, followed by their de novo recombination into meta-kerateine hydrogels, sponges and films. The kerateine fractions were characterized using electrophoresis and mass spectrometry, which revealed that the α-fraction contained complexes of type I and type II keratins and that the γ-fraction was primarily protein fragments of the α-fraction along with three proteins of the KAP-1 family. Meta-kerateine materials with increased amounts of γ-kerateines showed diminished physical, mechanical and biological characteristics. Most notably, materials with higher γ-content formed less elastic and less solid-like hydrogels and sponges that were less hydrolytically stable. In addition, a model biological assay showed that meta-kerateine films with greater amounts of γ-kerateines were less supportive of hepatocyte attachment. Investigation into the mechanism of attachment revealed that hepatocyte adhesion to meta-kerateines is not mediated by the β1 integrin subunit, despite the presence of LDV binding motifs within the type I α-keratins. This work to define the role of protein composition on biomaterial function is essential for the optimization of keratin biomaterials for biomedical applications.

DNA from keratinous tissue. Part I: hair and nail

Keratinous tissues such as nail, hair, horn, scales and feather have been used as a source of DNA for over 20 years. Particular benefits of such tissues include the ease with which they can be sampled, the relative stability of DNA in such tissues once sampled, and, in the context of ancient genetic analyses, the fact that sampling generally causes minimal visual damage to valuable specimens. Even when freshly sampled, however, the DNA quantity and quality in the fully keratinized parts of such tissues is extremely poor in comparison to other tissues such as blood and muscle - although little systematic research has been undertaken to characterize how such degradation may relate to sample source. In this review paper we present the current understanding of the quality and limitations of DNA in two key keratinous tissues, nail and hair. The findings indicate that although some fragments of nuclear and mitochondrial DNA appear to be present in almost all hair and nail samples, the quality of DNA, both in quantity and length of amplifiable DNA fragments, vary considerably not just by species, but by individual, and even within individual between hair types.

Disposition kinetics of selenium in healthy volunteers following therapeutic shampoo treatment

This study was aimed at documenting the kinetic time courses of selenium (Se) in accessible biological matrices of volunteers following controlled applications of therapeutic shampoo containing Se, to better elucidate the mechanisms by which shampoo-Se accumulates in hair and hence estimate the contribution of this source to total Se body burden. Ten healthy volunteers were exposed to Se-shampoo three times a week over a month. Blood, hair and toenail concentrations along with daily urinary excretions were repeatedly measured over an 18-month period following the onset of application. Over the entire study period, blood concentrations of Se (range: 127-233μg/l) and daily urinary excretions (range: 11.9-150μg/d) remained within baseline range of the general population. Conversely, during shampoo application, mean Se concentrations in hair reached transitional levels of 89μg/g while, following cessation of treatment, a mono-exponential decrease was observed with a mean half-life of 4.5 weeks. Two of the volunteers also exhibited an increase in toenail concentrations of Se during the study period. Results show that Se-shampoo does not contribute significantly to total Se body burden, as assessed from blood and urine levels. Differences observed between blood and urine time courses as compared to hair profiles and the presence of Se on hair grown before treatment indicates an adsorption on hair; however, the gradual decrease in Se concentrations in successive centimeters of hair grown following the application period suggests a concomitant absorption from the scalp during treatment with subsequent excretion in hair.

A Review of Keratin-Based Biomaterials for Biomedical Applications

Advances in the extraction, purification, and characterization of keratin proteins from hair and wool fibers over the past century have led to the development of a keratin-based biomaterials platform. Like many naturally-derived biomolecules, keratins have intrinsic biological activity and biocompatibility. In addition, extracted keratins are capable of forming self-assembled structures that regulate cellular recognition and behavior. These qualities have led to the development of keratin biomaterials with applications in wound healing, drug delivery, tissue engineering, trauma and medical devices. This review discusses the history of keratin research and the advancement of keratin biomaterials for biomedical applications.

K25 (K25irs1), K26 (K25irs2), K27 (K25irs3), and K28 (K25irs4) represent the type I inner root sheath keratins of the human hair follicle

The recent elucidation of the human type I keratin gene domain allowed the completion of the so far only partially characterized subcluster of type I keratin genes, KRT25-KRT28 (formerly KRT25A-KRT25D), representing the counterparts of the type II inner root sheath (IRS) keratin genes, KRT71-KRT74 (encoding proteins K71-K74, formerly K6irs1-K6irs4). Here, we describe the expression patterns of the type I IRS keratin proteins K25-K28 (formerly K25irs1-K25irs4) and their mRNAs. We found that K25 (K25irs1), K27 (K25irs3), and K28 (K25irs4) occur in the Henle layer, the Huxley layer, and in the IRS cuticle. Their expression extends from the bulb region up to the points of terminal differentiation of the three layers. In contrast, K26 (K25irs2) is restricted to the upper IRS cuticle. Apart from the three IRS layers, K25 (K25irs1), K27 (K25irs3), and K28 (K25irs4) are also present in the hair medulla. Based on previous, although controversial claims of the occurrence in the IRS of various "classical" epithelial keratins, we undertook a systematic study using antibodies against the presently described human epithelial and hair keratins and show that the type I keratins K25-K28 (K25irs1-K25irs4) and the type II keratins K71-K74 (K6irs1-K6irs4) represent the IRS keratins of the human hair follicle.

Characterization of the omega class of glutathione transferases

The Omega class of cytosolic glutathione transferases was initially recognized by bioinformatic analysis of human sequence databases, and orthologous sequences were subsequently discovered in mouse, rat, pig, Caenorhabditis elegans, Schistosoma mansoni, and Drosophila melanogaster. In humans and mice, two GSTO genes have been recognized and their genetic structures and expression patterns identified. In both species, GSTO1 mRNA is expressed in liver and heart as well as a range of other tissues. GSTO2 is expressed predominantly in the testis, although moderate levels of expression are seen in other tissues. Extensive immunohistochemistry of rat and human tissue sections has demonstrated cellular and subcellular specificity in the expression of GSTO1-1. The crystal structure of recombinant human GSTO1-1 has been determined, and it adopts the canonical GST fold. A cysteine residue in place of the catalytic tyrosine or serine residues found in other GSTs was shown to form a mixed disulfide with glutathione. Omega class GSTs have dehydroascorbate reductase and thioltransferase activities and also catalyze the reduction of monomethylarsonate, an intermediate in the pathway of arsenic biotransformation. Other diverse actions of human GSTO1-1 include modulation of ryanodine receptors and interaction with cytokine release inhibitory drugs. In addition, GSTO1 has been linked to the age at onset of both Alzheimer's and Parkinson's diseases. Several polymorphisms have been identified in the coding regions of the human GSTO1 and GSTO2 genes. Our laboratory has expressed recombinant human GSTO1-1 and GSTO2-2 proteins, as well as a number of polymorphic variants. The expression and purification of these proteins and determination of their enzymatic activity is described.

Keratins of the Human Hair Follicle

Substantial progress has been made regarding the elucidation of differentiation processes of the human hair follicle. This review first describes the genomic organization of the human hair keratin gene family and the complex expression characteristics of hair keratins in the hair-forming compartment. Sections describe the role and fate of hair keratins in the diseased hair follicle, particularly hereditary disorders and hair follicle-derived tumors. Also included is a report on the actual state of knowledge concerning the regulation of hair keratin expression. In the second part of this review, essentially the same principles are applied to outline more recent and, thus, occasionally fewer data on specialized epithelial keratins expressed in various tissue constituents of the external sheaths and the companion layer of the follicle. A closing outlook highlights issues that need to be explored further to deepen our insight into the biology and genetics of the hair follicle.

A role for the 1A and L1 rod domain segments in head domain organization and function of intermediate filaments: structural analysis of trichocyte keratin

A dynamic model is proposed to explain how the 1A and linker L1 segments of the rod domain in intermediate filament (IF) proteins affect the head domain organization and vice versa. We have shown in oxidized trichocyte IF that the head domain sequences fold back over and interact with the rod domain. This phenomenon may occur widely in reduced IF as well. Its function may be to stabilize the 1A segments into a parallel two-stranded coiled coil or something closely similar. Under differing reversible conditions, such as altered states of IF assembly, or posttranslational modifications, such as phosphorylation etc., the head domains may no longer associate with the 1A segment. This could destabilize segment 1A and cause the two alpha-helical strands to separate. Linker L1 would thus act as a hinge and allow the heads to function over a wide lateral range. This model has been explored using the amino acid sequences of the head (N-terminal) domains of Type I and Type II trichocyte keratin intermediate filament chains. This has allowed several quasi-repeats to be identified. The secondary structure corresponding to these repeats has been predicted and a model has been produced for key elements of the Type II head domain. Extant disulfide cross-link data have been used as structural constraints. A model for the head domain structure predicts that a twisted beta-sheet region may wrap around the 1A segment and this may reversibly stabilize a coiled-coil conformation for 1A. The evidence in favor of the swinging head model for IF is discussed.

Expression of human hair keratin basic 1 in pilomatrixoma. A study of 128 cases

Hard keratins are expressed in normal hair and nails, and are characterized by a higher cysteine content than cytokeratins. Previous studies have suggested a coexpression of hard keratins and cytokeratins in pilomatrixoma, a benign follicular tumour which could originate from the hair matrix. Human hair keratin basic 1 (hHb1) is a newly characterized hair keratin which is expressed specifically by cortical cells of the normal hair shaft. A preliminary study has suggested that hHb1 could be expressed in pilomatrixoma. In order to confirm this hypothesis, we have studied a series of 128 pilomatrixomas by in situ hybridization, using a 35S-labelled hHb1-specific probe. The anti-sense probe was used as a negative control. Among these pilomatrixomas, six were early cases, 60 were classified into the intermediate stage (either fully developed or early regressive cases) and 62 were late regressive tumours made of shadow cells only. Forty-seven tumours showed hHb1 expression (37%), all being intermediate stage pilomatrixomas. The areas positively stained by the probe were band-like structures made of transitional cells only, which were very close to cells showing tricholemmal keratinization features. Neither the basophilic matrix cells nor the shadow cells expressed hHb1. Our results suggest that pilomatrixomas can differentiate towards cortical cells during their maturation process, as this keratin is specifically expressed in the cortex of the normal hair shaft. These data are consistent with previous studies which showed the expression of a hard keratin group in transitional cells by immunohistochemistry. The histogenesis of basophilic cells of pilomatrixoma is controversial, but it is likely that transitional cells represent an equivalent of the hair cortex.

Hard alpha-keratin intermediate filament chains: substructure of the N- and C-terminal domains and the predicted structure and function of the C-terminal domains of type I and type II chains

The quantity of sequence data now available for both Type I and Type II hard alpha-keratin IF proteins makes it possible to analyze their N- and C-terminal domains and ascertain features of likely structural and/or functional importance. The N-terminal domains of both chain types can be divided into acidic (NA) and basic (NB) subdomains, where NA is 29 and 34 residues long, respectively, for Type I and II chains and is located immediately adjacent to the end of the rod domain. NB constitutes the remainder of the N-terminal domain and is about 27 and 70 residues long for the two chain types, respectively. The glycine residue contents, however, are high in NA(I) and NB(II), but low in NA(II) and NB(I). Subdomain NB(II) contains four consecutive nonapeptide quasirepeats of the form GGGFGYRSX. The C-terminal domain of Type I chains, termed C(I), is characterized by a PCX motif repeated 10 times, 7 of them contiguously. From an analysis of the conformation of like peptides from crystal structures it has been shown that this region will probably adopt a polyproline II left-handed helical structure with three residues per turn. In contrast, the C-terminal domain of Type II hard alpha-keratin chains (known as C(II)) contains a periodic distribution of hydrophobicities that, together with other predictive techniques, allow its conformation (a twisted four-stranded antiparallel beta-sheet) to be predicted with some degree of confidence. In addition, it is possible to suggest two partners with which this domain will interact. The first is with segment L12 in the rod domain and the second is with another C(II) domain in an antiparallel neighboring molecule. The latter possibility appears most likely. In either case the aggregation would likely serve to stabilize the molecular assembly through the interaction of two beta-sheets via their apolar faces and, in so doing, would position a number of cysteine residues in external positions that would allow them to form a number of covalent disulfide bonds with other molecules.

The role of keratin proteins and their genes in the growth, structure and properties of hair

The importance of wool in the textile industry has inspired extensive research into its structure since the 1960s. Over the past several years, however, the hair follicle has increased in significance as a system for studying developmental events and the process of terminal differentiation. The present chapter seeks to integrate the expanding literature and present a broad picture of what we know of the structure and formation of hair at the cellular and molecular level. We describe in detail the hair keratin proteins and their genes, their structure, function and regulation in the hair follicle, and also the major proteins and genes of the inner and outer root sheaths. We discuss hair follicle development with an emphasis on the factors involved and describe some hair genetic diseases and transgenic and gene knockout models because, in some cases, they stimulate natural mutations that are advancing our understanding of cellular interactions in the formation of hair.

Genomic characterization of the human type I cuticular hair keratin hHa2 and identification of an adjacent novel type I hair keratin gene hHa5

Hair keratins, a subset of the keratin multigene family expressed in hard keratinizing structures, previously have been thought to comprise four members of each subfamily, designated Ha1-4 (type I) and Hb1-4 (type II), which are differentially expressed in the cuticle and cortex of the hair follicle. This report describes the genomic cloning and sequencing of the human type I cuticular hair keratin hHa2, as well as the identification of a previously unknown human type I hair keratin gene. The 12.5-kilobase pair genomic clone ghkI2.12, obtained by hybridization of a human genomic deoxyribonucleic acid library with a 3'-complementary deoxyribonucleic acid probe of hHa2, as well as the partially overlapping 14.4-kilobase pair genomic clone ghkI2.17, isolated using a 5'-fragment of clone ghkI2.12, allowed the characterization of the entire hHa2 gene. The gene displays the same exon/intron structure as two previously characterized type I mouse and sheep hair/wool keratin genes with strict positional conservation of the six introns in the region coding for the central alpha-helix. At the 5'-extremity of clone ghkI2.17, i.e., approximately 8.0 kilobase pairs upstream of the hHa2 gene and oriented in the same transcriptional direction, lies the gene for a hitherto unknown human type I hair keratin. Clone ghkI2.17 contains partial sequence information for this gene beginning with intron 5 and extending to the end of the gene. Screening of a human scalp complementary deoxyribonucleic acid library with a 3'-fragment of the gene yielded a full length complementary deoxyribonucleic acid clone of the new hair keratin, which in continuation of the current nomenclature for hair keratins was termed hHa5. Remarkably, the hHa5 gene, which contains an additional 7th intron in its 3'-noncoding region, is expressed mainly in supramatricial cells and lowermost cortical cells of the hair bulb and thus constitutes a very early component of hair morphogenesis. Our results confirm the type specific clustering of keratin genes and indicate that the human type I hair keratin subfamily contains more members than previously assumed.

The region coding for the helix termination motif and the adjacent intron 6 of the human type I hair keratin gene hHa2 contains three natural, closely spaced polymorphic sites

Mutations in distinct sites of epidermal keratins, in particular in the helix initiation and termination regions, cause human genodermatoses due to faulty intermediate filament formation. Extension of this observation to human hereditary hair and nail diseases includes population analyses of human hair keratin genes for natural sequence variations in the corresponding sites. Here we report on a large-scale genotyping of the short helix termination region (HTR) of the human type I cortical hair keratins hHa1, a3-I, and a3-II, and the cuticular hair keratin hHa2. We describe two polymorphic loci, P1 and P2, exclusively in the cuticular hHa2 gene, both creating dimorphic protein variants. P1 is due to a C to T mutation in a CpG element leading to a threonine to methionine substitution; P2 concerns a serine codon AGT that also occurs as an asparagine coding variant AAC. A third polymorphism, P3, is linked with a C to T point mutation located at the very beginning of intron 6. The three polymorphic sites are clustered in a 39-nucleotide sequence of the hHa2 gene. Both allelic frequency calculations in individuals of different races and pedigree studies indicate that the two-allelic hHa2 variants resulting from P1 and P2 occur ubiquitously in a ratio of about 1:1 (P1) and 2:1 (P2) respectively in our survey, and are clearly inherited as Mendelian traits. A genotype carrying both mutations simultaneously on one allele could not be detected in our sampling, and there was no association of a distinct allelic hHa2 variant with the known ethnic form variations of hairs. Sequence comparisons of the HTR of hHa2 with those of other type I hair keratins including the hHa2-ortholog from chimpanzee provide evidence that the P1- and P2-linked mutations must have occurred very early in human evolution and that the two P2-associated codon variants may be the result of two independent point mutations in an ancestral AGC serine codon. These data describe natural polymorphisms in the HTR of a member of the keratin multigene family.

A cDNA encoding the human type I hair keratin hHal

A full-length cDNA of a human type I hair keratin was isolated that encodes a protein of 416 amino acids. Northern blot analysis shows that the mRNA is present in human scalp but not in hairless skin. Based on sequence homology comparisons with the four known mouse type I hair keratins mHal-4 the keratin could be identified as the human hair keratin hHal.

Sequence and expression of human hair keratin genes

Normal hair growth and differentiation requires co-ordinate expression of many hair specific structural protein genes. It has been established that one of the 4 major groups of hair structural proteins, low-sulphur hair keratins, belongs to the intermediate filament (IF) multigene family. Hair keratin IF proteins differ from those of other epithelia as they contain cysteine-rich terminal domains allowing more extensive disulphide bonding to the high-sulphur hair matrix proteins. Until recently, little information concerning the primary sequence of hair keratins was available but cloning of some mouse hair and sheep wool keratins has now been reported. Using these sequences, we have polymerase chain reaction (PCR) amplified genomic fragments of human hair-specific keratin IF genes and isolated cosmid clones containing full length genes. We have sequenced part of these genes and studied their expression in human hair follicles. Hair specific keratin fragments were amplified from placental gDNA by PCR primed with synthetic oligonucleotides. Fragments were cloned and sequenced after ligation into pGEM-3Z and labelled riboprobes were generated for in situ hybridization on human skin sections. A human cosmid library was screened with PCR fragments and clones encoding human hair keratin genes were characterised by southern hybridization and sequencing. The type I human hair-specific keratin clones obtained (HaKA1-b2, 386 bp; hHaKA1-XH1, 1202 bp) encoded 2B helix, C-terminal and 3'nc regions and were 65% homologous to mouse sequences. The type II hair keratin clone (hHaKB2-1, 829 bp) also encoded 2B helix and C-terminal regions and was 95% homologous to mouse. In situ hybridization on human skin sections showed a specific reaction with precortical cells of the hair follicle. One human cosmid clone, isolated with the hHaKB2-1 probe, contained two type II hair keratin genes about 7 kb apart, each of which had 9 exons spanning approximately 6 kb. The coding sequences were homologous to mouse cDNA (77-88%). These human hair-specific keratin clones are useful molecular tools for studies of hair differentiation.

Human hair production by scalp samples grafted onto nude mice. Biochemical data on normal human hair and the genetic defect trichothiodystrophy

The authors report on a laboratory model for continuous production of human hair during long periods of time. This study shows that the amino acid composition of hairs collected in situ from human scalp was similar to that of terminal hairs produced by the donors' scalp follicles grafted and maintained onto nude mice. A similar experiment was performed with scalp samples from a foetus with trichothiodystrophy (TTD). The amino acid analysis of TTD lanugo hairs and of the TTD shafts produced by grafted scalp specimens was consistent with findings published in the literature: severe decrease of cys (< 50% of control values) and moderate decrease of thr and pro (80% of control values or less) with an increase of ala-asp-ile-leu-lys-met-phe (120% of control values or more). These changes indicate a decrease of high sulphur proteins (HSP) and consequently a relative increase of keratins. Furthermore, when foetal scalp samples were grafted, the lanugo hairs transformed into terminal hairs along with normal initiation of melanisation. Hence, keratin and HSP gene expression and regulation of melanogenesis in the normal and genetically defective TTD human hair follicle grafts appear to be independent of systemic host-related factors, at least during a 6 months follow-up period after grafting. The present experimental evidence further supports conclusions gained from previous assays with normal and TTD variant scalp grafts, i.e. that the nude mouse bearing human scalp specimens may serve as a clinically relevant laboratory model for evaluating regulation of normal and abnormal gene expression in the hair follicle under well controlled experimental conditions.