The keratin BIIIB gene family: isolation of cDNA clones and structure of a gene and a related pseudogene

Spatiotemporal Expression and Haplotypes Identification of KRT84 Gene and Their Association with Wool Traits in Gansu Alpine Fine-Wool Sheep

Keratin (K) is a major protein component of hair and is involved in hair growth and development. In this study, we analysed the expression, localization, and polymorphism of the K84 gene (KRT84) in Gansu Alpine Fine-wool sheep using immunofluorescence, RT-qPCR, and PARMS (penta-primer amplification refractory mutation system). Haplotypes of KRT84 were also constructed and their relationship with wool traits analysed. It was revealed that KRT84 was highly expressed in hair follicles, including the inner root sheath, outer root sheath, and hair medulla and at all six lamb ages investigated from 1 to 270 days of age. Three SNPs were detected in KRT84 exon 1, and they formed three haplotypes (named H1, H2, and H3) and six genotypes. Analyses revealed an association between haplotype combinations (diplotypes) and the mean fibre curvature, mean staple length, mean staple strength, mean fibre diameter, the coefficient of variation of fibre diameter, and comfort factor for these sheep. These results suggest that KRT84 is of importance in determining several key traits in Gansu Alpine Fine-wool sheep and that the gene could possibly be used as a genetic marker for wool trait selection in these sheep.

The Complexity of the Ovine and Caprine Keratin-Associated Protein Genes

Sheep (Ovis aries) and goats (Capra hircus) have, for more than a millennia, been a source of fibres for human use, be it for use in clothing and furnishings, for insulation, for decorative and ceremonial purposes, or for combinations thereof. While use of these natural fibres has in some respects been superseded by the use of synthetic and plant-based fibres, increased accounting for the carbon and water footprint of these fibres is creating a re-emergence of interest in fibres derived from sheep and goats. The keratin-associated proteins (KAPs) are structural components of wool and hair fibres, where they form a matrix that cross-links with the keratin intermediate filaments (KIFs), the other main structural component of the fibres. Since the first report of a complete KAP protein sequence in the late 1960s, considerable effort has been made to identify the KAP proteins and their genes in mammals, and to ascertain how these genes and proteins control fibre growth and characteristics. This effort is ongoing, with more and more being understood about the structure and function of the genes. This review consolidates that knowledge and suggests future directions for research to further our understanding.

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.

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.

Characterization of the Promoter Regions of Two Sheep Keratin-Associated Protein Genes for Hair Cortex-Specific Expression

The keratin-associated proteins (KAPs) are the structural proteins of hair fibers and are thought to play an important role in determining the physical properties of hair fibers. These proteins are activated in a striking sequential and spatial pattern in the keratinocytes of hair fibers. Thus, it is important to elucidate the mechanism that underlies the specific transcriptional activity of these genes. In this study, sheep KRTAP 3–3 and KRTAP11-1 genes were found to be highly expressed in wool follicles in a tissue-specific manner. Subsequently, the promoter regions of the two genes that contained the 5′ flanking/5′ untranslated regions and the coding regions were cloned. Using an in vivo transgenic approach, we found that the promoter regions from the two genes exhibited transcriptional activity in hair fibers. A much stronger and more uniformly expressed green fluorescent signal was observed in the KRTAP11-1-ZsGreen1 transgenic mice. In situ hybridization revealed the symmetrical expression of sheep KRTAP11-1 in the entire wool cortex. Consistently, immunohistochemical analysis demonstrated that the pattern of ZsGreen1 expression in the hair cortex of transgenic mice matches that of the endogenous KRTAP11-1 gene, indicating that the cloned promoter region contains elements that are sufficient to govern the wool cortex-specific transcription of KRTAP11-1. Furthermore, regulatory regions in the 5′ upstream sequence of the sheep KRTAP11-1 gene that may regulate the observed hair keratinocyte specificity were identified using in vivo reporter assays.

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.

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.

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.

Identification of differentially expressed genes during a wool follicle growth cycle induced by prolactin

The wool follicles of New Zealand Wiltshire sheep can be induced to undergo growth cycles by manipulating circulating prolactin levels. Altered patterns of gene expression through this cycle were examined using differential display, and nine sequence tags for differentially expressed genes were isolated. Four of these tags were identified as fragments of known genes, encoding a wool keratin, KRTAP3.2, a desmosome component, desmoglein 1, an epithelial cell marker, stratifin, and a protein kinase, Clk3. All four genes were shown to be downregulated in telogen skin compared with anagen. In situ hybridization showed that all had localization patterns which included cells that are absent in telogen. The stratifin tag was used to clone a cDNA that incorporated a complete open-reading frame for ovine stratifin. Ovine stratifin is similar to the human form, showing only six single residue differences in the predicted amino acid sequence. Stratifin probably acts as a regulator of other proteins involved in trichocyte cell cycling and differentiation. Clk3 is involved in regulating RNA splicing. KRTAP3.2 and Dsg1 both play structural roles in hair follicles. The other five tags, including two representing genes that were upregulated during catagen, could not be identified by homology. Differential display is an effective means of identifying genes involved in follicle function and, potentially, of genes controlling the growth cycle.

Hair follicle has a novel anagen-specific protein, mKAP13

To identify the anagen hair follicle-specific proteins, we screened the cDNA library prepared from the murine skins of anagen phase by the differential hybridization technique. Fifty-four cDNA clones expressed specifically in anagen phase were isolated, and most were found to correspond to known proteins in the hair follicles. Alternatively, we isolated a cDNA clone encoding a novel protein that possessed an entire open reading frame of 501 base pairs. This protein with a molecular weight of 17.9 kDa has no specific motifs nor significant homology to proteins already reported, although it contains some direct repeats that are often observed in intermediate filament-associated proteins and has a similar amino acid composition as a member of them. Northern blot analysis demonstrates that the transcript of this protein is skin specific, and that it is present in mid- and late anagen but not in catagen, telogen, and early anagen phases. The transcript appears to be expressed specifically in the keratogenous zone of the cortical cells of hair follicles, as exhibited by in situ hybridization. Furthermore, immunohistochemical study confirms that the protein is distributed in the cytoplasms of the keratinizing cortical cells and is undetected in the completely keratinized ones. These results suggest that this protein can be identified as a new member of intermediate filament-associated proteins and is related to the keratinization of the cortical cell layer in mouse hair. Therefore, we have termed this novel protein mKAP13 according to the unified nomenclature.

Expression of a wool intermediate filament keratin transgene in sheep fibre alters structure

Alteration of the protein composition of the wool fibre via transgenesis with sheep wool keratin and keratin associated protein (KAP) genes may lead to production of fibre types with improved processing and wearing qualities. Using this approach, we have demonstrated that high level cortical-specific expression of a wool type II intermediate filament (IF) keratin gene, K2.10, leads to marked alterations in both the microstructure and macrostructure of the wool fibres, which have higher lustre and reduced crimp. Analysis of mRNA found reduced levels of transcripts from endogenous cortical type I (p < 0.05) and type II (p < 0.01) keratin IF genes and from the KAP8 (p < 0.001) and KAP2 (p < 0.01) gene families. Examination of protein composition revealed an altered ratio in the keratin type II protein family of the wool fibre cortex. Whilst the over-expressed K2.10 transgene product constituted the majority of keratin type II IF protein, it appeared unable to form heterodimers with much of the expressed endogenous keratin type I IF. In comparison with non-transgenic sheep, fewer IF microfibrils were visible in the cortical cells of fibres from transgenics. The combined effect on fibre structure was disruption of the formation of orthocortical and paracortical cells in the fibre cortex, a factor which could account for the reduction in fibre crimp. No effects upon transcript or protein levels, or fibre microstructure or macrostructure were observed in transgenic sheep expressing the transgene at lower levels, indicating that subtle changes to the gene expression profile in sheep wool follicles can be tolerated. The data here also illustrate that control over endogenous transcript levels in the cortex results when factors acting on the endogenous keratin type I, keratin type II and KAP gene sequences are sequestered by the active K2.10 transgene locus. Moreover, interference to a transcriptional hierarchy shared by keratin and KAP genes may occur prior to establishment of the orthocortical and paracortical compartments of the follicle cortex, at the level of the chromatin.

Structure and hair follicle-specific expression of genes encoding the rat high sulfur protein B2 family

High sulfur proteins are cysteine-rich proteins synthesized during the differentiation of hair matrix cells, and form hair fibers in association with hair keratin intermediate filaments. Rat high sulfur protein B2 genes were isolated after screening of a rat genomic library using the cDNA as a probe. Sequence analysis of a 4 kb fragment revealed two high sulfur protein genes, B2E and B2F. Both genes lacked introns, with B2F being located at 2 kb downstream of B2E. The 5' flanking regions of both genes had TATA and CAAT boxes, and consensus sequences of B2 genes. The upstream region of B2F had possible AP-1 and Sp-1 binding elements. The high sulfur protein B2E and B2F, which have putative 188 and 122 amino acids, respectively, comprised four distinct domains with a characteristic repetitive sequence. In situ hybridization indicated that the mRNA of high sulfur protein B2 was specifically localized in the cortex of the hair shaft, and northern blot analysis indicated that the expression of B2 increased in anagen and decreased in telogen, suggesting that high sulfur protein B2 synthesized in cortical cells during anagen contributes to the production of hair fibers.

Characterization and chromosomal localization of human hair-specific keratin genes and comparative expression during the hair growth cycle

During anagen, cell proliferation in the germinative matrix of the hair follicle gives rise to the fiber and inner root sheath. The hair fiber is constructed from structural proteins belonging to four multigene families: keratin intermediate filaments, high-sulfur matrix proteins, ultra high-sulfur matrix proteins, and high glycine-tyrosine proteins. Several hair-specific keratin intermediate filament proteins have been characterized, and all have relatively cysteine-rich N- and C-terminal domains, a specialization that allows extensive disulfide cross-linking to matrix proteins. We have cloned two complete type II hair-specific keratin genes (ghHb1 and ghHb6). Both genes have nine exons and eight introns spanning about 7 kb and lying about 10 kb apart. The structure of both genes is highly conserved in the regions that encode the central rod domain but differs considerably in the C-terminal coding and noncoding sequences, although some conservation of introns does exist. These genes have been localized to the type II keratin cluster on chromosome 12q13 by fluorescence in situ hybridization. They, and their type I partner ghHa1, are expressed in differentiating hair cortical cells during anagen. In cultured follicles, ghHa1 expression declined in cortical cells and was no longer visible after 6 d, whereas the basal epidermal keratin hK14 appeared in the regressing matrix. The transition from anagen to telogen is marked by downregulation of hair cortical specific keratins and the appearance of hK14 in the epithelial sac to which the telogen hair fiber is anchored. Further studies of the regulation of these genes will improve our understanding of the cyclical molecular changes that occur as the hair follicle grows, regresses, and rests.

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.

Genetic variation in Australian Merino sheep

Variation at 22 gene loci was investigated in a flock of Australian Merino sheep using restriction fragment length polymorphism (RFLP) analysis. Polymorphism was observed at 20 loci, including loci for wool keratin, hormone and immunoglobulin light chain genes. Eleven loci yielded unambiguous genotypes suitable for population data analysis. Average heterozygosity, determined from these and two monomorphic loci, was estimated as 0.107 (SE = 0.024). Average heterozygosity excluding all monomorphic data as estimated at 0.377 (SE = 0.031), which is comparable with human RFLP heterozygosities for loci chosen in the same way that we selected sheep loci.

The commercial and agricultural applications of animal transgenesis

The potential for commercial application of transgenic technologies in domestic animals is discussed in relation to the areas where a significant impact on agriculture might be expected. These are the endocrine system, novel biochemical pathways, structural proteins of milk and of textile fibers, and the immune system. Manipulation of the endocrine system has been investigated for some years and it is clear that very accurate control is needed over gene expression if this approach is to prove commercially useful. The area most advanced in commercial application is the production of high-value pharmaceutical proteins in the mammary glands of domestic animals. Other applications that are discussed remain to be proven in larger animals despite being demonstrated laboratory test animals. These include a functional cysteine biosynthetic pathway and a functional glyoxylate cycle transferred from bacteria to mice, and alterations to the proteins of hair that change the physical properties of the resultant fibers. Research is also actively directed toward novel approaches for providing domestic animals with resistance to insects.

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.

Isolation and characterization of a novel hair follicle-specific gene, Hacl-1

We have isolated a hair-follicle-specific gene, termed hacl-1, from a cDNA library of ICR mouse skin. Hacl-1 is expressed specifically in skin, and its mRNA level is correlated with the active state of hair follicles in developmental and regenerative processes of hair. Its mRNA is approximately 1 kilobase pairs (kb). Its cDNA was completely co-linear with the genomic clone, indicating that the hacl-1 gene is composed of one exon. The hacl-1 gene has an open reading frame of 579 base pairs (bp). The deduced amino acid sequence showed six direct repeats of a decapeptide on the C-terminal side. The repetitive unit contains a CQP motif, which is present in repetitive peptide sequences of some hair- and epidermal-cell-specific proteins. In situ hybridization with a 3' untranslated region of the hacl-1 cDNA as a probe showed that hacl-1 was expressed specifically in the keratogenous zone of the cortical cells of the hair shaft. No other components of hair follicles or epidermis showed a positive signal. Thus, hacl-1 is a novel, hair-follicle-specific gene.

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

The abomasal or intravenous infusion of sulphur-containing amino acids such as cysteine or methionine into sheep on low-quality diets increases the sulphur content of the wool by increasing the synthesis of proteins containing a cysteine content of approximately 30 mol %. To investigate the molecular and cellular basis of this nutritional effect, quantitative analyses of wool keratin mRNA and protein levels, and follicle cortical cell type, were undertaken in sheep intravenously infused with cysteine. Northern blot analyses revealed that the mRNA levels of one gene family encoding cysteine-rich keratin-associated proteins (KAP4 family) expressed in the wool follicle cortex, increased approximately 5-6 times. Furthermore, the response was rapid as the mRNA levels increased approximately 3.5 times after 1 d of the cysteine infusion and, by 1 d post-infusion, they had fallen, approaching their basal level. No changes in the mRNA levels encoding the intermediate filament or the other keratin-associated protein families of lower cysteine content were observed. Concomitantly, two-dimensional polyacrylamide gel electrophoresis analysis of wool proteins showed a striking increase in the abundance of a group of cysteine-rich keratin-associated proteins in the wool by the end of the infusion period, returning to basal levels by 3 weeks later. At the cellular level, KAP4 expression was localized to the follicle paracortical cells, and the proportion of paracortical cells and the extent of KAP4 expression paralleled the changes in the cysteine infusion status of the sheep.

Isolation and characterization of a sheep cysteine-rich cuticle keratin pseudogene

The cysteine-rich keratin proteins of the hair cuticle are derived from a multigene family that has been highly conserved during mammalian evolution. We have recently characterized one cuticle keratin gene isolated from a sheep lambda library, and Southern blot analysis of that clone suggested the presence of a second related gene. In the present paper sequencing of the second gene has now indicated that it is a pseudogene, a finding supported by a lack of expression in vivo. The pseudogene appears to have arisen by gene duplication, possibly from the adjacent functional gene. Key mutations seem to have occurred in the promoter and processing signals of this gene to render it non-functional and two in-frame termination codons are present in the coding region. A possible recombination point between sequences encoding glycine-rich repeats was identified that could have lead to the creation of the in-frame termination codons.

Regulation of keratin gene expression in hair follicle differentiation

In hair growth, as the follicle bulb cells rapidly differentiate into either cortical or cuticle hair keratinocytes, about 50-100 keratin genes are transcriptionally activated. However, this complexity can be reduced to several, highly conserved gene families. In studying the regulation of keratin gene expression in the hair follicle we have isolated genes from most of these families and have examined their expression patterns by in situ hybridization. In the cortical keratinocytes striking patterns of keratin gene expression exist, suggesting that different transcriptional hierarchies operate in the various cell types. Comparisons of the keratin gene promoter regions indicates conserved sequence motifs that could be involved in determining these cell specificities. Similarly, we have isolated related sheep and human cuticle keratin genes and find conserved DNA motifs and expression patterns in cuticle cell differentiation. Additionally, the expression of sheep wool follicle IF and high-sulfur keratin genes in transgenic mice suggests that the regulatory DNA elements and proteins of hair keratin genes are functionally conserved between mammals.

The genetic engineering of production traits in domestic animals

The transfer of recombinant DNA by microinjection of embryo pronuclei provides a novel approach to the manipulation of production traits in domestic animals. In this review, several of the key areas currently under investigation are examined and their progress evaluated. These include the manipulation of the endocrine system by altered growth hormone genes and the modification of animal biochemistry by the introduction of the cysteine biosynthetic pathway and the glyoxylate cycle. The possibilities inherent in the alteration of structural proteins important to domestic animal productivity, and some ethical issues relevant to the release of modified animals are also considered. The experimental information obtained so far in the area indicates that transcriptional regulation of the genes and a thorough understanding of the physiological processes involved are both important factors in the practical application of the technique to the improvement of animal productivity.

An ultrahigh-sulphur keratin gene of the human hair cuticle is located at 11q13 and cross-hybridizes with sequences at 11p15

A human hair cuticle ultrahigh-sulphur keratin Q (UHSK) gene (KRN1) has been mapped by Southern analysis of a somatic cell hybrid panel and by in situ hybridization. A probe containing the coding region of this gene mapped to 11pter- greater than 11q21 using the hybrid cell panel and on in situ hybridization mapped to two regions on chromosome 11: the distal part of 11p15, most likely 11p15.5, and the distal part of 11q13, most likely 11q13.5. A probe from the 3' noncoding region of KRN1 mapped to 11q13.5 indicating that this was the map location of the cloned gene. The sequence of 11p15.5 is termed KRN1-like (KRN1L). The results reveal that the cuticle UHSK gene family is clustered in the human genome.

Structure and expression of genes for a class of cysteine-rich proteins of the cuticle layers of differentiating wool and hair follicles

The major histological components of the hair follicle are the hair cortex and cuticle. The hair cuticle cells encase and protect the cortex and undergo a different developmental program to that of the cortex. We report the molecular characterization of a set of evolutionarily conserved hair genes which are transcribed in the hair cuticle late in follicle development. Two genes were isolated and characterized, one expressed in the human follicle and one in the sheep follicle. Each gene encodes a small protein of 16 kD, containing greater than 50 cysteine residues, ranging from 31 to 36 mol% cysteine. Their high cysteine content and in vitro expression data identify them as ultra-high-sulfur (UHS) keratin proteins. The predicted proteins are composed almost entirely of cysteine-rich and glycine-rich repeats. Genomic blots reveal that the UHS keratin proteins are encoded by related multigene families in both the human and sheep genomes. Tissue in situ hybridization demonstrates that the expression of both genes is localized to the hair fiber cuticle and occurs at a late stage in fiber morphogenesis.