Size Polymorphisms in the Human Ultrahigh Sulfur Hair Keratin-Associated Protein 4, KAP4, Gene Family

Recent omics advances in hair aging biology and hair biomarkers analysis

Aging is a complex natural process that leads to a decline in physiological functions, which is visible in signs such as hair graying, thinning, and loss. Although hair graying is characterized by a loss of pigment in the hair shaft, the underlying mechanism of age-associated hair graying is not fully understood. Hair graying and loss can have a significant impact on an individual's self-esteem and self-confidence, potentially leading to mental health problems such as depression and anxiety. Omics technologies, which have applications beyond clinical medicine, have led to the discovery of candidate hair biomarkers and may provide insight into the complex biology of hair aging and identify targets for effective therapies. This review provides an up-to-date overview of recent omics discoveries, including age-associated alterations of proteins and metabolites in the hair shaft and follicle, and highlights the significance of hair aging and graying biomarker discoveries. The decline in hair follicle stem cell activity with aging decreased the regeneration capacity of hair follicles. Cellular senescence, oxidative damage and altered extracellular matrix of hair follicle constituents characterized hair follicle and hair shaft aging and graying. The review attempts to correlate the impact of endogenous and exogenous factors on hair aging. We close by discussing the main challenges and limitations of the field, defining major open questions and offering an outlook for future research.

Non-invasive assessment of hair regeneration in androgenetic alopecia mice in vivo using two-photon and second harmonic generation imaging

The identification of crucial targets for hair regrowth in androgenetic alopecia (AGA) involves determining important characteristics and different stages during the process of hair follicle regeneration. Traditional methods for assessing key features and different stages of hair follicle primarily involve taking skin tissue samples and determining them through various staining or other methods. However, non-invasive assessment methods have been long sought. Therefore, in this study, endogenous fluorescence signals from skin keratin and second harmonic signals from skin collagen fibers were utilized as probes, two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) imaging techniques were employed to non-invasively assess hair shafts and collagen fibers in AGA mice in vivo. The TPEF imaging technique revealed that the alternation of new and old hair shafts and the different stages of the growth period in AGA mice were delayed. In addition, SHG imaging found testosterone reduced hair follicle area and miniaturized hair follicles. The non-invasive TPEF and SHG imaging techniques provided important methodologies for determining significant characteristics and different stages of the growth cycle in AGA mice, which will facilitate future non-invasive assessments on human scalps in vivo and reduce the use of animal testing.

DNA and protein analyses of hair in forensic genetics

Hair is one of the most common pieces of biological evidence found at a crime scene and plays an essential role in forensic investigation. Hairs, especially non-follicular hairs, are usually found at various crime scenes, either by natural shedding or by forcible shedding. However, the genetic material in hairs is usually highly degraded, which makes forensic analysis difficult. As a result, the value of hair has not been fully exploited in forensic investigations and trials. In recent years, with advances in molecular biology, forensic analysis of hair has achieved remarkable strides and provided crucial clues in numerous cases. This article reviews recent developments in DNA and protein analysis of hair and attempts to provide a comprehensive solution to improve forensic hair analysis.

Short Communication: A highly polymorphic caprine keratin-associated protein gene identified and its effect on cashmere traits

Five keratin-associated protein 6 genes (KRTAP6) have been identified in sheep and variation in some KRTAP6 has been associated with wool fibre diameter-related traits, but none of these homologues has been identified in goats. In this study, we reported the identification of the sheep KRTAP6-5 homologue on goat chromosome 1 and PCR-single strand conformation polymorphism analysis in 300 Longdong cashmere goats revealed the existence of twelve variant sequences. Both coding region and 3'UTR of the putative caprine KRTAP6-5 displayed a biggest sequence similarity to ovine KRTAP6-5 gene. This suggested that the gene represents caprine KRTAP6-5 sequences, and these sequences composed twenty three genotypes which was the most polymorphism gene in KRTAPs that have been studied. Among these sequences, fifteen nucleotide substitutions and a 24-bp insertion/detection were identified. Variation in goat KRTAP6-5 was associated with variation in mean fibre diameter, suggesting that KRTAP6-5 is worthy of further study in the context of variation in cashmere traits.

Deletions in the KAP6-1 gene are associated with fiber traits in cashmere-producing goats

Keratin-associated proteins (KAPs) are important structural components of fibers that predominantly present in the ortho-cortex. These proteins form a cross-linked network with keratin intermediate filaments (KIFs), thus producing a strong hair shaft. The keratin-associated protein 6-1 gene (KAP6-1) is a member of the KAPs family that has a potential correlation with fiber traits. In this study, we investigated the influence of KAP6-1 sequence polymorphisms on the fiber characteristics of a Chinese cashmere-producing goat breed (n = 844). Two main variants were found, including a three base pair (bp) deletion (namely B) and a 36-bp deletion (namely C), while the reference genotype of KAP6-1 was named A. Among them, the B variant was first reported on cashmere goats. This study then correlated these genotypes with the collected fiber data to investigate the potential association of these variants. The results showed that variant A is associated with decreased fiber diameter (p < 0.01), while variant C is associated with deceased fiber length (p < 0.01). These two related variants of the KAP6-1 gene have potential applications as gene-makers to improve the fiber diameter and length in cashmere-producing goats.

Wool Keratin-Associated Protein Genes in Sheep-A Review

The importance of sheep's wool in making textiles has inspired extensive research into its structure and the underlying genetics since the 1960s. Wool keratin-associated proteins (KAPs) are a key structural component of the wool fibre. The characterisation of the genes encoding these proteins has progressed rapidly with advances in the nucleotide and protein sequencing. This review describes our knowledge of ovine KAPs, their categorisation into families, polymorphism in the proteins and genes, the clustering and chromosomal location of the genes, some characteristics of gene expression and some potential effects of the KAPs on wool traits. The extent and nature of genetic variation in wool KAP genes and its association with fibre characteristics, provides an opportunity for the development of gene-markers for selective breeding of sheep to produce better wool with properties highly matched to specific end-uses.

Mammalian keratin associated proteins (KRTAPs) subgenomes: disentangling hair diversity and adaptation to terrestrial and aquatic environments

Background

Adaptation of mammals to terrestrial life was facilitated by the unique vertebrate trait of body hair, which occurs in a range of morphological patterns. Keratin associated proteins (KRTAPs), the major structural hair shaft proteins, are largely responsible for hair variation.

Results

We exhaustively characterized the KRTAP gene family in 22 mammalian genomes, confirming the existence of 30 KRTAP subfamilies evolving at different rates with varying degrees of diversification and homogenization. Within the two major classes of KRTAPs, the high cysteine (HS) subfamily experienced strong concerted evolution, high rates of gene conversion/recombination and high GC content. In contrast, high glycine-tyrosine (HGT) KRTAPs showed evidence of positive selection and low rates of gene conversion/recombination. Species with more hair and of higher complexity tended to have more KRATP genes (gene expansion). The sloth, with long and coarse hair, had the most KRTAP genes (175 with 141 being intact). By contrast, the “hairless” dolphin had 35 KRTAPs and the highest pseudogenization rate (74% relative to the 19% mammalian average). Unique hair-related phenotypes, such as scales (armadillo) and spines (hedgehog), were correlated with changes in KRTAPs. Gene expression variation probably also influences hair diversification patterns, for example human have an identical KRTAP repertoire as apes, but much less hair.

Conclusions

We hypothesize that differences in KRTAP gene repertoire and gene expression, together with distinct rates of gene conversion/recombination, pseudogenization and positive selection, are likely responsible for micro and macro-phenotypic hair diversification among mammals in response to adaptations to ecological pressures.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-779) contains supplementary material, which is available to authorized users.

Autozygome sequencing expands the horizon of human knockout research and provides novel insights into human phenotypic variation

The use of autozygosity as a mapping tool in the search for autosomal recessive disease genes is well established. We hypothesized that autozygosity not only unmasks the recessiveness of disease causing variants, but can also reveal natural knockouts of genes with less obvious phenotypic consequences. To test this hypothesis, we exome sequenced 77 well phenotyped individuals born to first cousin parents in search of genes that are biallelically inactivated. Using a very conservative estimate, we show that each of these individuals carries biallelic inactivation of 22.8 genes on average. For many of the 169 genes that appear to be biallelically inactivated, available data support involvement in modulating metabolism, immunity, perception, external appearance and other phenotypic aspects, and appear therefore to contribute to human phenotypic variation. Other genes with biallelic inactivation may contribute in yet unknown mechanisms or may be on their way to conversion into pseudogenes due to true recent dispensability. We conclude that sequencing the autozygome is an efficient way to map the contribution of genes to human phenotypic variation that goes beyond the classical definition of disease.

Characterization of the human hair keratin-associated protein 2 (KRTAP2) gene family

Hair keratin-associated proteins (KRTAPs) are one of the major structural components of the hair shaft. Approximately 100 KRTAP genes have been identified in humans to date, with each of the genes classified into a number of families based on their sequence homology and the nature of the repeat structures. The biophysical features of KRTAPs, however, have remained largely unknown. In this study, we investigated the characteristics of the human KRTAP2 family members at the DNA, RNA, and protein levels. We initially found that these genes had various size polymorphisms that were mainly due to differences in the length of the 3'-noncoding sequences. Reverse transcriptase-PCR experiments further detected the presence of KRTAP2 transcripts in plucked human hairs. Using indirect immunofluorescence with an anti-KRTAP2 antibody, we found that there was a predominant expression of the KRTAP2 proteins in the keratinizing zone of the human hair shaft cortex. In addition, we showed that the KRTAP2 proteins interacted with each other and preferentially bound to hair keratins, but not to epithelial keratins. Finally, we determined that the head domain of the hair keratins was essential for the affinity to KRTAP2 proteins. Our results further enhance the crucial roles of KRTAPs in hair shaft keratinization in humans.

Hair greying is associated with active hair growth

BACKGROUND

Hair greying is an obvious sign of ageing in humans. White (nonpigmented) hair is thicker than black (pigmented) hair. The growth rate of white hair is also significantly higher than that of black hair. However, the mechanism underlying this is largely unknown.

OBJECTIVES

To examine the association between hair greying and hair growth patterns by evaluating expression of the genes or proteins related to hair growth in white and black hairs.

METHODS

Morphological characteristics were observed in eyebrow and scalp hairs. The differential expression of genes was analysed in black and white hairs from human scalp by a microarray analysis. Reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry for genes and proteins related to hair growth were performed in black and white hairs.

RESULTS

Keratin and keratin-associated protein (KRTAP) genes in white hair were upregulated at least two-fold in comparison with black hair in a microarray analysis. Upregulation of selected keratin genes and KRTAP4 isoform genes in white hair was validated by RT-PCR. Immunoreactivity for KRT6, KRT14/16 and KRT25 was increased in the hair follicle of white hair compared with black hair. Gene expression of fibroblast growth factor 5 (FGF5) was downregulated in white hair compared with black hair. However, gene expression of FGF7 was upregulated in white hair compared with black hair.

CONCLUSIONS

Expression of genes and proteins associated with active hair growth is upregulated in white (nonpigmented) hair compared with black (pigmented) hair. These results suggest that hair greying is associated with active hair growth.

An updated nomenclature for keratin-associated proteins (KAPs)

Most protein in hair and wool is of two broad types: keratin intermediate filament-forming proteins (commonly known as keratins) and keratin-associated proteins (KAPs). Keratin nomenclature was reviewed in 2006, but the KAP nomenclature has not been revised since 1993. Recently there has been an increase in the number of KAP genes (KRTAPs) identified in humans and other species, and increasingly reports of variation in these genes. We therefore propose that an updated naming system is needed to accommodate the complexity of the KAPs. It is proposed that the system is founded in the previous nomenclature, but with the abbreviation sp-KAPm-nL*x for KAP proteins and sp-KRTAPm-n(p/L)*x for KAP genes. In this system “sp” is a unique letter-based code for different species as described by the protein knowledge-based UniProt. “m” is a number identifying the gene or protein family, “n” is a constituent member of that family, “p” signifies a pseudogene if present, “L” if present signifies “like” and refers to a temporary “place-holder” until the family is confirmed and “x” signifies a genetic variant or allele. We support the use of non-italicised text for the proteins and italicised text for the genes.

This nomenclature is not that different to the existing system, but it includes species information and also describes genetic variation if identified, and hence is more informative. For example, GenBank sequence JN091630 would historically have been named KRTAP7-1 for the gene and KAP7-1 for the protein, but with the proposed nomenclature would be SHEEP-KRTAP7-1*A and SHEEP-KAP7-1*A for the gene and protein respectively. This nomenclature will facilitate more efficient storage and retrieval of data and define a common language for the KAP proteins and genes from all mammalian species.

Emerging issues with the current keratin-associated protein nomenclature

Keratin associated proteins (KAPs) are a class of proteins that associate with keratin intermediate filament proteins through disulphide linkages to give fibres such as hair and wool their unique properties. Up to 90 proteins from some 25 families have been identified and this does not include polymorphic variants of individual proteins within these families. The existence of this diverse group of proteins has been known for some 75 years but, despite this, there is still no universally accepted nomenclature for them. This paper sets out the case for revising the current system to deal with this nomenclature issue.

Ageing processes influence keratin and KAP expression in human hair follicles

In many cultures, a youthful look is strictly linked to strong and healthy hair. Source of the hair fibre is the hair follicle, a highly specialized skin appendage. Biological alterations because of intrinsic or extrinsic stimuli can destabilize this perfectly organized system, thus effecting hair growth or metabolism. Also, ageing could be characterized as a disturbance in this well-balanced machinery. Albeit the predominant symptom of hair ageing, greying, is addressed in a plurality of research activities, further age-related changes, e.g. related to hair structure, remain obscure. Therefore, we characterized hair follicles of two volunteer panels (below 25 years, above 50 years) on the molecular level, especially focussing on alterations influencing gene expression of keratins and keratin-associated proteins. We showed that concordantly to other biological systems the hair follicle undergoes several modifications during the ageing process associated among others with a significant decline in these structural proteins. Providing strategies to fight against these age-related changes is a challenge for hair science.

Diversity of the glycine/tyrosine-rich keratin-associated protein 6 gene (KAP6) family in sheep

Keratin-associated proteins (KAPs) are structural components of wool and variation in them may affect wool characteristics. In this study, we used PCR-SSCP to analyse the ovine KAP6 family which encodes glycine and tyrosine-rich KAPs. Five unique PCR-SSCP patterns were detected in the 250 sheep investigated. Between two and five patterns were observed in individual sheep and none with only one pattern was detected. This suggests the amplicons were heterogeneous and derived from more than one locus. To analyse these heterogeneous PCR amplicons, a sequencing approach using SSCP to separate individual amplified sequences, was developed. Using this approach, five DNA sequences (A-E) representing five unique PCR-SSCP patterns were obtained. D was identical to a published ovine KAP6-1 sequence (GenBank accession no. M95719), whereas the others were novel, but the closest homology was with KAP6 sequences from human, sheep, goats and cattle. The five ovine KAP6 sequences could be assigned into three distinct groups. B and D were identical to each other, with the exception of a 57-bp deletion/insertion and a single nucleotide polymorphism (SNP) in the 3'-UTR region. These appear to be allelic variants of ovine KAP6-1. A and C could form another group, as they were similar to each other (with only one synonymous SNP), but different to the other sequences. This group appears to be related to a sheep KAP6 amino acid sequence, and represent allelic variation at another KAP6 locus (designated KAP6-2). The remaining sequence E did not show high sequence homology with either the KAP6-1 or KAP6-2 sequences, but exhibited homology with a bovine KAP6-3 sequence, with the exception of a deletion/insertion of 30 nucleotides. This suggests that E represents ovine KAP6-3. This sequence was detected in only 11% of the sheep investigated, suggesting either a KAP6-3 null allele, or failure to amplify allleles. These results suggest that ovine KAP6 is a complex gene family, that is not only comprised multiple loci, but that is also polymorphic.

Characterization and expression analysis of KAP7.1, KAP8.2 gene in Liaoning new-breeding cashmere goat hair follicle

Keratin-associated protein is one of the major structural proteins of the hair, whose content in hair has important effect on the quality of cashmere. In order to study the relationship between HGTKAP gene expression and cashmere fineness, the quantitative real-time RT-PCR (qRT-PCR) was firstly used to detect the levels of KAP7.1, KAP8.2 gene expression in the primary and secondary hair follicles; semi-quantitative RT-PCR was used to detect whether KAP7.1, KAP8.2 gene are expressed in heart, liver, spleen, lung, kidney tissues; and in situ hybridization(ISH) to detect KAP7.1 gene expression location. qRT-PCR result showed that the expression of both KAP7.1 and KAP8.2 gene in the secondary hair follicles are significantly higher than that in the primary follicles, relative quantitative analysis obtained that KAP7.1 was 2.28 times, while KAP8.2 was 2.71 times. Semi-quantitative RT-PCR results revealed that KAP 7.1 and KAP8.2 mRNA were not detected in the heart, liver, spleen, lung and kidney tissues, demonstrating that KAP7.1 and KAP8.2 were specially expressed in hair follicles, participating in hair formation. Moreover, KAP7.1 gene has a strong expression in the cortical layer, inner root sheath of the primary follicles and the cortical layer, inner root sheath and hair matrix of the secondary hair follicles by ISH analysis. Taken together, the evidence presented here indicated that in the formation of cashmere and wool, differential expression of these two genes in the primary and secondary hair follicles may have an important role in regulating the fiber diameter.

Molecular evolution of the keratin associated protein gene family in mammals, role in the evolution of mammalian hair

Background

Hair is unique to mammals. Keratin associated proteins (KRTAPs), which contain two major groups: high/ultrahigh cysteine and high glycine-tyrosine, are one of the major components of hair and play essential roles in the formation of rigid and resistant hair shafts.

Results

The KRTAP family was identified as being unique to mammals, and near-complete KRTAP gene repertoires for eight mammalian genomes were characterized in this study. An expanded KRTAP gene repertoire was found in rodents. Surprisingly, humans have a similar number of genes as other primates despite the relative hairlessness of humans. We identified several new subfamilies not previously reported in the high/ultrahigh cysteine KRTAP genes. Genes in many subfamilies of the high/ultrahigh cysteine KRTAP genes have evolved by concerted evolution with frequent gene conversion events, yielding a higher GC base content for these gene sequences. In contrast, the high glycine-tyrosine KRTAP genes have evolved more dynamically, with fewer gene conversion events and thus have a lower GC base content, possibly due to positive selection.

Conclusion

Most of the subfamilies emerged early in the evolution of mammals, thus we propose that the mammalian ancestor should have a diverse KRTAP gene repertoire. We propose that hair content characteristics have evolved and diverged rapidly among mammals because of rapid divergent evolution of KRTAPs between species. In contrast, subfamilies of KRTAP genes have been homogenized within each species due to concerted evolution.

Biology of the wool follicle: an excursion into a unique tissue interaction system waiting to be re-discovered

Wool fibres are hairs and the term 'wool' is usually restricted to describe the fine curly hairs that constitute the fleece produced by sheep. In a broader sense, it can be used to describe the fleeces produced by related species such as goat or yak. Research into the biology of wool growth and the structure of the wool fibre has been driven by the demands of the wool industry to improve both the efficiency of growing wool and the quality of the product. Well beyond this very applied perspective however, the wool follicle is a unique basic research model for the life sciences in general. These unique features include, to name just a few selected examples, accessibility for studying the molecular controls involved in branching of secondary epithelial-mesenchymal structures, the photoperiod-dependence of regenerating tissue interaction systems, the origin of fibre curliness and follicle wave pattern formation, and the effect of alterations in nutrient supply on epithelial growth and fibre structure. In this review, investigation of growth processes in the formation of the wool fibre is broadly surveyed. The relevance and potential for practical outcomes through characterization of wool follicle genes are discussed and particular features of the wool follicle contributing to our knowledge of the biology of hair growth are highlighted. The practical potential of gene discovery in wool research is the provision of molecular markers for selective breeding and for altering wool growth and wool structure by other biological pathways such as sheep transgenesis that could lead to novel wool properties. In this background, the current review attempts to revive general interest in the fascinating biology of the wool follicle which is not only of profound economic and practical importance but offers an exquisite, highly instructive research model for addressing key questions of modern biology.

Human hair keratin-associated proteins (KAPs)

Elucidation of the genes encoding structural proteins of the human hair follicle has advanced rapidly during the last decade, complementing nearly three previous decades of research on this subject in other species. Primary among these advances was both the characterization of human hair keratins, as well as the hair keratin associated proteins (KAPs). This review describes the currently known human KAP families, their genomic organization, and their characteristics of expression. Furthermore, this report delves into further aspects, such as polymorphic variations in human KAP genes, the role that KAP proteins might play in hereditary hair diseases, as well as their modulation in several different transgenic mouse models displaying hair abnormalities.

Human hair keratin-associated proteins

Hair keratin-associated proteins (KAP) are a major component of the hair fiber, and play crucial roles in forming a strong hair shaft through a cross-linked network with keratin intermediate filaments (KIF), which are produced from hair keratins. Recently, the study of human KAP has advanced significantly. So far, five clusters of human KAP genes have been characterized, leading to the identification of more than 80 individual human KAP genes. In situ hybridization studies have demonstrated sequential and spatial expression patterns of these KAP members in differential portions of the hair fiber cortex and cuticle. Furthermore, several human KAP genes have size polymorphisms that are mainly because of variable numbers of cysteine-rich repeat segments, and the patterns of some of these size variants are distinct between different human populations.

Spontaneous alopecia areata-like hair loss in one congenic and seven inbred laboratory mouse strains

Alopecia areata (AA) research has been hampered by the lack of suitable animal models for use in experimental procedures. AA-like hair loss has been observed in several species, including dogs, cats, horses, cattle, and nonhuman primates; however, these examples are isolated cases in outbred species of large size, limiting their use in AA research. Inbred rodent strains are ideal research models. C3H/HeJ mice can develop spontaneous AA-like hair loss and have previously been advanced as a suitable experimental model. The search for additional mouse strains with AA-like hair loss has continued. Nonscarring, inflammatory, spontaneously reversible hair loss has been observed in individual mice from several inbred mouse strains. Aside from C3H/HeJ mice, an AA-like phenotype has been observed in the substrain C3H/HeJBir, with an expression frequency of 5%. Up to 10% of individuals in an A/J mouse colony have been confirmed to develop patchy AA-like hair loss. Isolated examples of AA have also been identified in C3H/HeN/J mice, C3H/OuJ mice, HRS/J+/hr heterozygous normal mice, CBA/CaHN-Btk(xid)/J mice, and BALB.2R-H2h2/Lil mice, each with a colony frequency of less than 1%. BALB.2R-H2h2/Lil mice may also have severe nail defects. AA is regarded as rare in nonhuman species; however, nonscarring inflammatory based alopecia has been identified in several mouse strains. These examples may represent different subtypes of the heterogeneous AA phenotype. Pathologic and genetic analysis of different AA affected mouse strains may contribute to understanding AA pathogenesis and elucidating susceptibility genes.