Dietary cysteine regulates the levels of mRNAs encoding a family of cysteine-rich proteins of wool

Wool fiber curvature is correlated with abundance of K38 and specific keratin-associated proteins

Curvature in mammalian fibers, such as wool and human hair, is an important feature of the functional trait of coat structure-it affects mechanical resilience and thermo-insulation. However, to examine the relationship between fiber curvature, ultrastructure and protein composition fiber diameter variability has to be minimal. To achieve this we utilised the progeny of straight-wool domestic sheep mutant rams (crimp mutants) and wild-type ewes. Proteomic and structural results of the resulting mutant/wild-type twin pairs confirmed that straight crimp mutant wool had a normal cuticle and the same cortical protein and ultrastructural building blocks as wild-type (crimpy) fibers but differed in the layout of its cortical cells and in the relative proportions of keratin (K) and keratin-associated proteins (KAPs). In the case of the crimp mutants (straight fibers), the orthocortex was distributed in a fragmented, annular ring, with some orthocortical cells near the central medulla, a pattern similar to that of straight hairs from humans and other mammals. Crimp mutant fibers were noted for the reduced abundance of some proteins in the high glycine-tyrosine class normally associated with the orthocortex, specifically the KAP6, KAP7, and KAP8 families, while proteins from the KAP16 and KAP19 were found in increased abundance. In addition to this, the type I keratin, K38, which is also associated with the orthocortex, was also found at lower abundance in the mutant fibers. Conversely, proteins from the ultra-high sulfur class normally associated with the paracortex, specifically the KAP4 and KAP9 families, were found in higher abundance.

Amino Acids in the Nutrition and Production of Sheep and Goats

In sheep and goats, amino acid nutrition is essential for the maintenance of health and productivity. In this review, we analysed literature, mostly from the past two decades, focusing on assessment of amino acid requirements, especially on the balance of amino acid profiles between ruminal microbial protein and animal production protein (foetal growth, body weight gain, milk and wool). Our aim was to identify amino acids that might limit genetic potential for production. We propose that much attention should be paid to amino acid nutrition of individuals with greater abilities to produce meat, milk or wool, or to nourish large litters. Moreover, research is warranted to identify interactions among amino acids, particularly these amino acids that can send positive and negative signals at the same time.

Diversity of Trichocyte Keratins and Keratin Associated Proteins

Wool and hair fibres are primarily composed of proteins of which the keratins and keratin associated proteins (KAPs) are the major component. Considerable diversity is known to exist within these two groups of proteins. In the case of the keratins two major families are known, of which there are 11 members in the acidic Type I family and 7 members in the neutral-basic Type II family. The KAPs are even more diverse than the keratins, with 35 families being known to exist when the KAPs found in monotremes, marsupials and other mammalian species are taken into consideration. Human hair and wool are known to have 88 and 73 KAPs respectively, though this number rises for wool when polymorphism within KAP families is included.

Cysteine Prevents the Reduction in Keratin Synthesis Induced by Iron Deficiency in Human Keratinocytes

L-cysteine is currently recognized as a conditionally essential sulphur amino acid. Besides contributing to many biological pathways, cysteine is a key component of the keratin protein by its ability to form disulfide bridges that confer strength and rigidity to the protein. In addition to cysteine, iron represents another critical factor in regulating keratins expression in epidermal tissues, as well as in hair follicle growth and maturation. By focusing on human keratinocytes, the aim of this study was to evaluate the effect of cysteine supplementation as nutraceutical on keratin biosynthesis, as well as to get an insight on the interplay of cysteine availability and cellular iron status in regulating keratins expression in vitro. Herein we demonstrate that cysteine promotes a significant up-regulation of keratins expression as a result of de novo protein synthesis, while the lack of iron impairs keratin expression. Interestingly, cysteine supplementation counteracts the adverse effect of iron deficiency on cellular keratin expression. This effect was likely mediated by the up-regulation of transferrin receptor and ferritin, the main cellular proteins involved in iron homeostasis, at last affecting the labile iron pool. In this manner, cysteine may also enhance the metabolic iron availability for DNA synthesis without creating a detrimental condition of iron overload. To the best of our knowledge, this is one of the first study in an in vitro keratinocyte model providing evidence that cysteine and iron cooperate for keratins expression, indicative of their central role in maintaining healthy epithelia.

Molecular characterization and expression pattern of a novel Keratin-associated protein 11.1 gene in the Liaoning cashmere goat (Capra hircus)

OBJECTIVE

An experiment was conducted to determine the relationship between the KAP11.1 and the regulation wool fineness.

METHODS

In previous work, we constructed a skin cDNA library and isolated a full-length cDNA clone termed KAP11.1. On this basis, we conducted a series of bioinformatics analysis. Tissue distribution of KAP11.1 mRNA was performed using semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis. The expression of KAP11.1 mRNA in primary and secondary hair follicles was performed using real-time PCR (real-time polymerase chain reaction) analysis. The expression location of KAP11.1 mRNA in primary and secondary hair follicles was performed using in situ hybridization.

RESULTS

Bioinformatics analysis showed that KAP11.1 gene encodes a putative 158 amino acid protein that exhibited a high content of cysteine, serine, threonine, and valine and has a pubertal mammary gland) structural domain. Secondary structure prediction revealed a high proportion of random coils (76.73%). Semi-quantitative RT-PCR showed that KAP11.1 gene was expressed in heart, skin, and liver, but not expressed in spleen, lung and kidney. Real time PCR results showed that the expression of KAP11.1 has a higher expression in catagen than in anagen in the primary hair follicles. However, in the secondary hair follicles, KAP11.1 has a significantly higher expression in anagen than in catagen. Moreover, KAP11.1 gene has a strong expression in inner root sheath, hair matrix, and a lower expression in hair bulb.

CONCLUSION

We conclude that KAP11.1 gene may play an important role in regulating the fiber diameter.

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.

Hair curvature: a natural dialectic and review

Although hair forms (straight, curly, wavy, etc.) are present in apparently infinite variations, each fibre can be reduced to a finite sequence of tandem segments of just three types: straight, bent/curly, or twisted. Hair forms can thus be regarded as resulting from genetic pathways that induce, reverse or modulate these basic curvature modes. However, physical interconversions between twists and curls demonstrate that strict one-to-one correspondences between them and their genetic causes do not exist. Current hair-curvature theories do not distinguish between bending and twisting mechanisms. We here introduce a multiple papillary centres (MPC) model which is particularly suitable to explain twisting. The model combines previously known features of hair cross-sectional morphology with partially/completely separated dermal papillae within single follicles, and requires such papillae to induce differential growth rates of hair cortical material in their immediate neighbourhoods. The MPC model can further help to explain other, poorly understood, aspects of hair growth and morphology. Separate bending and twisting mechanisms would be preferentially affected at the major or minor ellipsoidal sides of fibres, respectively, and together they exhaust the possibilities for influencing hair-form phenotypes. As such they suggest dialectic for hair-curvature development. We define a natural-dialectic (ND) which could take advantage of speculative aspects of dialectic, but would verify its input data and results by experimental methods. We use this as a top-down approach to first define routes by which hair bending or twisting may be brought about and then review evidence in support of such routes. In particular we consider the wingless (Wnt) and mammalian target of rapamycin (mTOR) pathways as paradigm pathways for molecular hair bending and twisting mechanisms, respectively. In addition to the Wnt canonical pathway, the Wnt/Ca(2+) and planar cell polarity (PCP) pathways, and others, can explain many alternatives and specific variations of hair bending phenotypes. Mechanisms for hair papilla budding or its division by bisection or fission can explain MPC formation. Epithelial-to-mesenchymal (EMT) and mesenchymal-to-epithelial (MET) transitions, acting in collaboration with epithelial-mesenchymal communications are also considered as mechanisms affecting hair growth and its bending and twisting. These may be treated as sub-mechanisms of an overall development from neural-crest stem cell (NCSC) lineages to differentiated hair follicle (HF) cell types, thus providing a unified framework for hair growth and development.

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.

Expression patterns of keratin intermediate filament and keratin associated protein genes in wool follicles

The catalogue of hair keratin intermediate filaments (KIFs) and keratin-associated proteins (KAPs) present in wool follicles is incomplete. The full coding sequences for three novel sheep KIFs (KRT27, KRT35 and KRT38) and one KAP (KRTAP4-3) were established in this study. Spatial expression patterns of these and other genes (KRT31, KRT85, KRTAP6-1 and trichohyalin) were determined by in situ hybridisation in wool follicles at synchronised stages of growth. Transcription proceeded in the order: trichohyalin, KRT27, KRT85, KRT35, KRT31, KRT38, KRTAP6-1 and KRTAP4-3, as determined by increasing distance of their expression zones from the germinal matrix in anagen follicles. Expression became gradually more restricted to the lower follicle during follicle regression (catagen), and ceased during dormancy (telogen). Some genes (KRT27, KRT31, KRT85 and KRTAP6-1), but not others, were expressed in cortical cells forming the brush-end, indicating specific requirements for the formation of this anchoring structure. The resumption of keratin expression was observed only in later stages of follicle reactivation (proanagen). KIF expression patterns in primary wool follicles showed general resemblance to their human homologues but with some unique features. Consistent differences in localisation between primary and secondary wool follicles were observed. Asymmetrical expression of KRT27, KRT31, KRT35, KRT85 and trichohyalin genes in secondary follicles were associated with bulb deflection and follicle curvature, suggesting a role in the determination of follicle and fibre morphology.

Characterization of the structural and molecular defects in fibres and follicles of the Merino felting lustre mutant

The felting lustre (FL) mutation found in Merino sheep results in a fleece that has a lustrous appearance and readily felts. This phenotype was described 50 years ago to result from the mutation of a single gene, but the molecular and cellular changes in the wool are not well understood. In this study, follicle and fibre material of FL mutant (n = 3) and normal control (n = 5) Merino ewes was compared using histological analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), real-time polymerase chain reaction (qPCR) and electron microscopy [scanning electron microscopy (SEM) and transmission electron microscopy (TEM)]. Histological examination suggested that follicle structure in FL mutants is essentially normal, while SDS-PAGE analysis found that some low molecular weight keratin-associated proteins (KAP) were present at much lower levels in FL wool. Examination of transcript prevalence revealed that the KAP6.1, KAP7 and KAP8 genes in FL mutant follicles are downregulated, while the KAP2.12 and KAP4.2 genes are upregulated. TEM analysis indicated that there is only one type of cortical cell, the paracortical cell, in the fibre of FL mutants, while there are paracortical and orthocortical cells in fibres of normal Merino sheep. In contrast, SEM suggested the surface topography of FL wool fibres is normal. The evidence presented here strongly suggests that the properties of FL wool can be ascribed, at least in part, to the lower content of high glycine/tyrosine proteins and the reduction in orthocortical cells in mutant wool fibres.

The differential expression of proteins in the cortical cells of wool and hair fibres

Three different cell types have been identified in the cortex of wool: orthocortex, mesocortex and paracortex. Fine wool fibres, particularly Merino sheep, are noted for their bilateral distribution of orthocortical and paracortical cells, with the latter following the concave side of the crimp wave. Furthermore, studies have indicated that the paracortex has a higher concentration of cysteine than the orthocortex. This has been supported by in situ hybridization studies in the follicle that have shown that sulphur-rich proteins are initially expressed on the paracortical side of the fibre, with some becoming more uniformly spread, laterally, over the entire fibre as the keratinization process progresses. In contrast, proteins high in glycine and tyrosine tend to be expressed initially on the orthocortical side of the follicle. While these in vitro studies have pointed to where specific proteins are located in the follicle, elucidating the situation for the mature fibre has been less easy. A range of approaches have been used to separate orthocortical and paracortical cells and these have only been able to provide evidence for a higher level of cysteine in the latter. Electrophoretic studies have found a number of differences in protein expression between the two sides but have not specifically identified which proteins. Thus, there appears to be good evidence for the paracortex containing a higher proportion of proteins in the ultra-high sulphur class but there is some uncertainty regarding the exact distribution of proteins high in glycine and tyrosine.

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.

Keratin gene expression in Merino sheep with divergent wool growth

South Australian Merino sheep were selected on the basis of high or low estimated breeding values (EBV) for wool growth rate (W), but with similar bodyweight, follicle density, and mean fibre diameter. Differences in the level of expression of keratin genes were examined in the skin of these sheep to test the hypothesis that divergence in EBV for wool growth is related to the production of wool proteins differing in sulfur (S) content. Further, it was proposed that this differential gene expression would be most pronounced when the supply of S amino acids to the animal was increased. Sheep selected for high EBV (+W) produced more wool per day than low EBV sheep (–W) (on average 32.5 v. 17.7 g/day clean wool, respectively; P < 0.05) but the S content of the wool did not differ between selection groups (2.77% v. 2.87% S, respectively; P = 0.2). Expression of keratin genes including keratin-associated protein KAP 2 (a high S gene), KAP 4 (an ultra-high S gene), KAP 6 (a high glycine/tyrosine gene), and the intermediate filament gene K 2.10, did not differ significantly between +W and –W groups. KAP 2 and K 2.10 each accounted for approximately 5% of the variation in wool growth rate (WGR) but expression of none of the genes examined was significantly related to the S content of the fibre produced. This suggests that differential keratin gene expression was not the source of genetic divergence in WGR. Instead the latter likely reflects a combination of differential cellular rate and growth processes (e.g. rate of bulb cell production, hypertrophy of cortical cells), differences in the relative production of inner root sheath and fibre from the follicle bulb cell population, or differential nutrient uptake into the follicle.

Characterization of human keratin-associated protein 1 family members

Keratin-associated proteins are involved in the formation of the cross-linked network of the keratin-intermediate filament proteins that support hair fibers. In recent years, several keratin-associated protein genes have been identified and become an attractive topic in hair research. More recently, we isolated two cDNA encoding novel members of the human keratin-associated protein 1 family (human keratin-associated protein 1.6 and human keratin-associated protein 1.7), and described their expression in the hair follicle by RNA in situ hybridization. A comparison of human keratin-associated protein 1.6 and human keratin-associated protein 1.7 with other human keratin-associated protein 1 members revealed that keratin-associated protein 1 proteins are fundamentally composed of five distinct domains, and that they can be classified primarily by a striking variation in double cysteine-containing pentapeptide repeats in the repetitive I domain. The sum of the data analyzed suggests that human keratin-associated protein 1 family genes may have arisen mainly through gene duplication of the cysteine-repeat motifs during evolution.

Characterization of a first domain of human high glycine-tyrosine and high sulfur keratin-associated protein (KAP) genes on chromosome 21q22.1

Analysis of the EBI/GeneBank(TM) data base using non-human hair keratin-associated protein (KAP) cDNA sequences as a query resulted in the identification of a first domain of high glycine-tyrosine and high sulfur KAP genes located on human chromosome 21q22.1. This domain, present on the DNA accession numbers and, was approximately 535 kb in size and contained 17 high glycine-tyrosine and 7 high sulfur KAP genes, as well as 9 KAP pseudogenes. Based on amino acid sequence comparisons of the encoded proteins, the KAP genes could be divided into seven high glycine-tyrosine gene families (KAP6-KAP8, and KAP19-KAP22) and four high sulfur gene families (KAP11, KAP13, KAP15, and KAP23). The high glycine-tyrosine genes described here appear to represent the complete set of this type of KAP genes present in the human genome. Both systematic cDNA isolation studies from an arrayed scalp cDNA library and in situ hybridization expression studies of all of the KAP genes identified in the 21q22.1 region revealed varying degrees and regions of expression of 11 members of the high tyrosine-glycine genes and 6 members of the high sulfur KAP genes in the hair forming compartment.

Polymorphisms in the human high sulfur hair keratin-associated protein 1, KAP1, gene family

Hair fiber differentiation and maturation involves the close interaction between hair keratins and their associated proteins, KAPs. Recently, a cluster of seven human KAP multigen families has been identified on chromosome 17q12-21 among which were four hKAP1 genes (hKAP1.1B, hKAP1.3, hKAP1.4, and hKAP1.5). In addition, there were previous as well as recent reports on four additional hKAP1 genes (hKAP1.1A, hKAP1.2, hKAP1.6, and hKAP1.7) with unknown chromosomal location. In this study, we have analyzed these eight hKAP1 genes in unrelated Japanese and Caucasian individuals and discovered that hKAP1.1A, hKAP1.6, and hKAP1.7 represent size polymorphisms of the hKAP1.1B gene. In addition, we show that hKAP1.2 as well as three hitherto unknown genes (hKAP1.8A, hKAP1.8B, and hKAP1.9) are size polymorphisms of the hKAP1.3 gene. In contrast, no polymorphic alleles were found for the hKAP1.4 and hKAP1.5 genes. We provide evidence that the polymorphic hKAP1.1B and hKAP1.3 alleles arose mainly by intragenic deletion and/or duplication events of distinct pentapeptide repeats typical for hKAP1 genes. We also demonstrate the occurrence of both frequent and rare population-specific hKAP1.1B and hKAP1.3 alleles, which were obviously generated after the divergence of the Caucasian and Japanese lineage. In addition, by means of a pan-hKAP1 antibody, we confirm the previous hKAP1 family mRNA localization data in the middle to upper cortex of the human anagen hair follicle.

hKAP1.6 and hKAP1.7, two novel human high sulfur keratin-associated proteins are expressed in the hair follicle cortex

Hair fiber differentiation involves the expression of both hair keratin intermediate filament proteins and their associated proteins, termed keratin-associated proteins. In this study, cDNA clones encoding two novel keratin-associated proteins were isolated from human hair follicle mRNA. The predicted amino acid sequence derived from these clones revealed that these proteins represent members of the human keratin-associated protein 1 family. They show strong sequence homology to two previously described keratin-associated protein 1 family members hKAP1.1 A and hKAP1.1B. We have called these new proteins hKAP1.6 and hKAP1.7, respectively. RNA in situ hybridization studies of human anagen hair follicles using a conserved probe for these four keratin-associated protein 1 members demonstrated the expression of this group in the differentiated portions of the hair cortex.

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.

A cluster of keratin-associated proteins on mouse chromosome 10 in the region of conserved linkage with human chromosome 21

A gene cluster of three to five high-cysteine keratin-associated proteins (KAPs) has been identified on mouse Chromosome 10 (MMU10) in the region of conserved linkage with human chromosome 21 (HSA21). One of these genes, Krtap12-1, has been sequenced in its entirety and shown to be an intronless gene encoding a predicted 130-amino-acid protein. Krtap12-1 is most closely related to two previously identified KAP4 genes, but variation in sequence and cysteine content suggests that it represents a new KAP family. Krtap12-1 is expressed in the skin of a 3-day-old mouse. The corresponding region of HSA21, between ITGB2 (integrin beta2) and PFKL (the liver isoform of phosphofructokinase), has proven refractory to cloning, and thus mapping of this region at high resolution has been problematic. Based on the KAP gene cluster position in mouse, evidence has been found for an orthologous human KAP cluster on HSA21q22.3, reinforcing the observation that comparative genomics can play an essential and practical role in determining mammalian genome organization.

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.

Isolation and characterization of genomic clones of human sequences presumably coding for hair cysteine-rich proteins

The major biochemical components of the mammalian hair are the intermediate filaments or keratins and the keratin associated proteins. Keratin associated proteins are classified into two groups (high-cysteine and high glycine-tyrosine-rich polypeptides) according to the content of these amino acids. Cysteine-rich group contains high sulphur (16-24% cysteine) and ultra-high sulphur (> 30% cysteine) proteins. We report here the identification of a human sequence presumably coding for a new ultra-high sulphur protein (hUHSp21) and the isolation and characterization of four genomic clones containing six related sequences. We also discuss the possibility that all the genes encoding keratin associated proteins are evolutionary related. These human clones should provide useful molecular tools for studies of hair differentiation and understanding of the molecular basis of human trichothiodystrophy.

Inhibition of polyamine synthesis alters hair follicle function and fiber composition

The activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase, two of the enzymes involved in the synthesis of the polyamines, were found to be high in follicle-rich homogenates of sheep skin, and to be responsive to the nutrition of the animal. Systemic provision of the inhibitor of ornithine decarboxylase, alpha difluoromethylornithine, markedly altered the length, diameter, and composition of the fiber, the last being accompanied by an increase in the proportion of the fiber occupied by paracortical cells and an increase in the level of mRNA encoding a cysteine-rich family of keratin proteins. The growth of wool follicles cultured in media containing alpha-difluoromethylornithine was not inhibited, even at high concentrations. In contrast, low concentrations of methylglyoxal (bis)guanylhydrazone, the inhibitor of S-adenosylmethionine decarboxylase, completely inhibited fiber growth in culture follicles. Addition of spermidine to the media overcame this inhibition but spermine had no effect. Further evidence that spermine is not required for normal follicle function was provided by incubating follicles with the specific inhibitor of spermine synthase, n-butyl-1,3-diaminopropane. This inhibitor, even at high concentrations, had no effect on fiber growth in vitro. Spermidine partially overcame the growth depression that occurred in follicles cultured in methionine-deficient media, suggesting that part of the requirement for methionine is for spermidine synthesis in the follicle. These investigations provide strong evidence that the polyamines in general , and spermidine in particular, play a major role in hair growth.

Characterization of a gene encoding a cysteine-rich keratin associated protein synthesized late in rabbit hair follicle differentiation

Many different cysteine-rich proteins are synthesized during hair follicle differentiation, forming part of the interstitial matrix between bundles of intermediate filaments. We have isolated a rabbit gene (rKAP4L), a member of a multigene family that encodes a small cysteine-rich hair keratin associated protein. This is the first complete gene sequence for this family. The rKAP4L gene is expressed in the cortex of rabbit pelage hair follicles at a late stage of hair follicle differentiation, well after the synthesis of the other major hair proteins, the intermediate filament and glycine/tyrosine-rich keratin associated proteins, has commenced. The protein contains 36 mol % cysteine, with a molecular size of 13593 daltons, and its sequence appears to be based on a pentapeptide repeat. It is predicted to adopt a folded conformation characterized by beta-turns interspersed with short stretches of beta-sheet or random coil.

Differential expression of genes encoding a cysteine-rich keratin family in the hair cuticle

In the hair follicle the cuticle develops as a thin layer of cells between the hair shaft cortex and the inner root sheath. Once the cuticle cells begin to differentiate they accumulate cysteine-rich granules in their cytoplasm but the identity of their constituent proteins has remained largely an enigma. In this report we show differential expression of a family of genes encoding cysteine-rich, glycine-rich keratins in the cuticle. Two clones of the sheep KAP5 gene family were isolated: the KAP5.4 cDNA encodes a protein of 190 amino acids (M(r) = 16,936) containing 32 mol% cysteine, 26 mol% glycine and the partial KAP5.5 cDNA encodes a protein of at least 197 amino acids (M(r) > or = 17,474) containing 29 mol% cysteine, 28 mol% glycine. The predicted amino acid sequences of the KAP5 family show extensive sequence conservation and all the proteins are composed almost entirely of cysteine-rich and glycine-rich repeats. Each KAP5 gene produces an approximately 1.5-kb mRNA species but the KAP5.4 and KAP5.5 mRNA levels appear to be severalfold greater than the KAP5.1 mRNA. Comparative tissue in situ hybridizations reveal a positive correlation between the onset of expression and follicle depth. For a given KAP5 gene two widely different cuticle expression patterns were noted amongst the follicle populations, and on the basis of follicle bulb cell kinetics they are consistent with expression in either sheep primary or secondary follicle types.