Genes for hair and avian keratins

Freeze-thaw cycles for biocompatible, mechanically robust scaffolds of human hair keratins

The keratin-based scaffolds are getting more and more attention in the application of tissue engineering. Though various approaches have been considered to improve the physical properties of these scaffolds, few succeeded in achieving the enhanced properties of the pure keratin scaffolds. Due to the presence of -OH, -NH₂ , >CO, and -SH on the extracted human hair keratin (HHK), the formation of hydrogen bonds and disulfide bridges could be triggered under certain conditions, leading to the self-cross-linking of HHK materials. Herein, a simple and green strategy was introduced, via freeze-thaw cycles of keratin solutions without addition of extraneous reagents, to obtain the mechanically robust HHK scaffolds. The comparative quantitation of residual -SH among the samples treated with 1, 5, and 9 cycles confirmed the oxidation in the thaw process for forming disulfide bonds. So, the equivalent thaw time was applied in this study, and three groups of the treated samples after 1, 5, and 9 cycles with an appropriate extension thaw time were prepared to solely investigate the effects of physical cross-linking networks, primarily by formation of hydrogen bonds, on the properties of the obtained scaffolds. The systematic assessments including swelling behavior, porosity, thermal analysis, compressive measurement, and microstructural observation confirmed that the repetitive freeze-thaw treatment contributed to mechanically robust scaffolds with good porous interconnectivity. The cell culturing experiments further verified that these HHK scaffolds had desirable cytocompatibility, permitting the proper proliferation, attachment, and infiltration. Accordingly, this study provided a simple and efficient method to obtain biocompatible, mechanically robust keratin scaffolds. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1452-1461, 2019.

Using scale and feather traits for module construction provides a functional approach to chicken epidermal development

Gene co-expression network analysis has been a research method widely used in systematically exploring gene function and interaction. Using the Weighted Gene Co-expression Network Analysis (WGCNA) approach to construct a gene co-expression network using data from a customized 44K microarray transcriptome of chicken epidermal embryogenesis, we have identified two distinct modules that are highly correlated with scale or feather development traits. Signaling pathways related to feather development were enriched in the traditional KEGG pathway analysis and functional terms relating specifically to embryonic epidermal development were also enriched in the Gene Ontology analysis. Significant enrichment annotations were discovered from customized enrichment tools such as Modular Single-Set Enrichment Test (MSET) and Medical Subject Headings (MeSH). Hub genes in both trait-correlated modules showed strong specific functional enrichment toward epidermal development. Also, regulatory elements, such as transcription factors and miRNAs, were targeted in the significant enrichment result. This work highlights the advantage of this methodology for functional prediction of genes not previously associated with scale- and feather trait-related modules.

Immunolocalization of a Histidine-Rich Epidermal Differentiation Protein in the Chicken Supports the Hypothesis of an Evolutionary Developmental Link between the Embryonic Subperiderm and Feather Barbs and Barbules

The morphogenesis of feathers is a complex process that depends on a tight spatiotemporal regulation of gene expression and assembly of the protein components of mature feathers. Recent comparative genomics and gene transcription studies have indicated that genes within the epidermal differentiation complex (EDC) encode numerous structural proteins of cornifying skin cells in amniotes including birds. Here, we determined the localization of one of these proteins, termed EDMTFH (Epidermal Differentiation Protein starting with a MTF motif and rich in Histidine), which belongs to a group of EDC-encoded proteins rich in aromatic amino acid residues. We raised an antibody against an EDMTFH-specific epitope and performed immunohistochemical investigations by light microscopy and immunogold labeling by electron microscopy of chicken embryos at days 14-18 of development. EDMTFH was specifically present in the subperiderm, a transient layer of the embryonic epidermis, and in barbs and barbules of feathers. In the latter, it partially localized to bundles of so-called feather beta-keratins (corneous beta-proteins, CBPs). Cells of the embryonic periderm, the epidermis proper, and the feather sheath were immunonegative for EDMTFH. The results of this study indicate that EDMTFH may contribute to the unique mechanical properties of feathers and define EDMTFH as a common marker of the subperiderm and the feather barbules. This expression pattern of EDMTFH resembles that of epidermal differentiation cysteine-rich protein (EDCRP) and feather CBPs and is in accordance with the hypothesis that a major part of the cyclically regenerating feather follicle is topologically, developmentally and evolutionarily related to the embryonic subperiderm.

Topographical mapping of α- and β-keratins on developing chicken skin integuments: Functional interaction and evolutionary perspectives

Avian integumentary organs include feathers, scales, claws, and beaks. They cover the body surface and play various functions to help adapt birds to diverse environments. These keratinized structures are mainly composed of corneous materials made of α-keratins, which exist in all vertebrates, and β-keratins, which only exist in birds and reptiles. Here, members of the keratin gene families were used to study how gene family evolution contributes to novelty and adaptation, focusing on tissue morphogenesis. Using chicken as a model, we applied RNA-seq and in situ hybridization to map α- and β-keratin genes in various skin appendages at embryonic developmental stages. The data demonstrate that temporal and spatial α- and β-keratin expression is involved in establishing the diversity of skin appendage phenotypes. Embryonic feathers express a higher proportion of β-keratin genes than other skin regions. In feather filament morphogenesis, β-keratins show intricate complexity in diverse substructures of feather branches. To explore functional interactions, we used a retrovirus transgenic system to ectopically express mutant α- or antisense β-keratin forms. α- and β-keratins show mutual dependence and mutations in either keratin type results in disrupted keratin networks and failure to form proper feather branches. Our data suggest that combinations of α- and β-keratin genes contribute to the morphological and structural diversity of different avian skin appendages, with feather-β-keratins conferring more possible composites in building intrafeather architecture complexity, setting up a platform of morphological evolution of functional forms in feathers.

Dynamic evolution of the alpha (α) and beta (β) keratins has accompanied integument diversification and the adaptation of birds into novel lifestyles

BACKGROUND

Vertebrate skin appendages are constructed of keratins produced by multigene families. Alpha (α) keratins are found in all vertebrates, while beta (β) keratins are found exclusively in reptiles and birds. We have studied the molecular evolution of these gene families in the genomes of 48 phylogenetically diverse birds and their expression in the scales and feathers of the chicken.

RESULTS

We found that the total number of α-keratins is lower in birds than mammals and non-avian reptiles, yet two α-keratin genes (KRT42 and KRT75) have expanded in birds. The β-keratins, however, demonstrate a dynamic evolution associated with avian lifestyle. The avian specific feather β-keratins comprise a large majority of the total number of β-keratins, but independently derived lineages of aquatic and predatory birds have smaller proportions of feather β-keratin genes and larger proportions of keratinocyte β-keratin genes. Additionally, birds of prey have a larger proportion of claw β-keratins. Analysis of α- and β-keratin expression during development of chicken scales and feathers demonstrates that while α-keratins are expressed in these tissues, the number and magnitude of expressed β-keratin genes far exceeds that of α-keratins.

CONCLUSIONS

These results support the view that the number of α- and β-keratin genes expressed, the proportion of the β-keratin subfamily genes expressed and the diversification of the β-keratin genes have been important for the evolution of the feather and the adaptation of birds into multiple ecological niches.

Comparative aspects of the inner root sheath in adult and developing hairs of mammals in relation to the evolution of hairs

The inner root sheath (IRS) allows the exit of hairs through the epidermal surface. The fine structure of monotreme and marsupial IRS and trichohyalin is not known. Using electron microscopy and immunocytochemistry, the localization of trichohyalin and transglutaminase have been studied in monotreme and marsupial hairs, and compared with trichohyalin localization in placental hairs. Trichohyalin in all mammalian species studied here is recognized by a polyclonal antibody against sheep trichohyalin. This generalized immunoreactivity suggests that common epitopes are present in trichohyalin across mammals. In differentiating IRS cells, trichohyalin granules of variable dimensions are composed of an immunolabelled amorphous matrix associated with a network of 10-12-nm-thick keratin filaments. Transglutaminase labelling is present among keratin bundles and trichohyalin granules, and in condensed nuclei of terminally differentiating cells of the inner root sheath. The IRS in monotreme hairs is multistratified but lacks a distinguishable Henle layer. Cornification of IRS determines the sculpturing of the fibre cuticle and later shedding from the follicle for the exit of the hair fibre on the epidermal surface. It is hypothesized that the stratification of IRS in Henle, Huxley and IRS cuticle layers is derived from a simpler organization, like that present in the IRS of monotremes. The IRS is regarded as a localized shedding/sloughing layer needed for the exit of hairs without injury to the epidermis. The formation of the IRS during the evolution of mammalian epidermis allowed the physiological exit of hairs produced inside the skin. The peculiar morphogenesis of hairs in possible primitive skins, such as those of the monotremes (mammals with some reptilian characteristics) or the tails of some rodents (a scaled skin), may elucidate the evolution of hairs. In monotreme and rodent tail skin, the dermal papilla remains localized on the proximal side of the hair peg and forms a hair placode with bilateral symmetry. The papilla is progressively surrounded by the down-growing hair peg until a dermal papilla with radial symmetry is formed. It is speculated that the progressive reduction of the extended dermal papilla of reptilian scales into small and deep papillae of therapsid reptiles produced hairs in mammals.

Fine structure of marsupial hairs, with emphasis on trichohyalin and the structure of the inner root sheath

The fine structure and cornification of marsupial hairs are unknown. The distribution of keratins, trichohyalin, and transglutaminase in marsupial hairs was studied here for the first time by electron microscopy and immunocytochemistry. The localization of acidic and basic keratins in marsupial hairs is similar to that of hairs in placental mammals, and the keratins are mainly localized in the outer root sheath and surrounding epidermis. Marsupial trichohyalin in both medulla and inner root sheath (IRS) cross-reacts with a trichohyalin antibody that recognizes trichohyalin across placental species, indicating a common epitope(s) among mammalian trichohyalin. Roundish to irregular trichohyalin granules are composed of a network of immunolabeled 10-15-nm-thick coarse filaments within an amorphous matrix in which a weak labeling for transglutaminases is present. This suggests that the enzyme, and its substrate trichohyalin, are associated in mature granules. Transglutaminase labeling mainly occurs in condensing chromatin of mature cells of the outer and inner root sheaths, suggesting formation of the nuclear envelope connected with terminal differentiation of these cells. In mature Huxley or Henle layers the filaments lose the immunolabeling for trichohyalin when they are reoriented into parallel rows linked by short bridges, thus suggesting that the filaments with their reactive epitopes are chemically modified during cornification, as seen in the IRS of hairs of placental mammals. The Huxley layer probably acts as a cushion, absorbing the tensions connected with the distalward movement of the growing hair fiber. Variations in stratification of the Huxley layer are probably related to the diameter of the hair shaft. The cytoplasmic and junctional connections between cells of the Huxley layer and the companion layer and the outer root sheath enhance the grip of the IRS and hair fiber within the follicle. The role of cells of the IRS in sculpturing the fiber cuticle and in the mechanism of shedding that allows the exit of hair on the epidermal surface in mammals are discussed.

A rapid extraction procedure of human hair proteins and identification of phosphorylated species

We developed a rapid and convenient extraction procedure of human hair proteins to examine their biochemical properties in detail. This procedure is based upon the fact that the combination of thiourea and urea in the presence of a reductant can effectively remove proteins from the cortex part of human hair. The extracted fraction mainly consisted of hard alpha-keratins with molecular masses of 40-60 kDa, matrix proteins with 12-18kDa, and minor components with 110-115kDa and 125-135kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The protein phosphorylation in human hair was investigated by immunoblotting with antibodies against phosphoserine, phosphothreonine and phosphotyrosine. We found serine phosphorylation in alpha-keratins and matrix proteins and threonine phosphorylation in alpha-keratins. The extraction was also found to be effective when wool, chicken feathers, rat hair and human nails were used as starting materials.

Keratin: a journey of three decades

During the past three decades, major progress has been made in our understanding of the processes which lead to the formation of a keratinized epidermis in normal and pathologic situations. Stimulated by clinical studies of exfoliative dermatitis and related diseases, a series of investigations have been performed which proved initially that the pathways and controls of epidermal protein synthesis were equivalent to protein synthetic pathways in all other tissues of the body. Keratin was identified as not only an insoluble protein which makes up the vast majority of the intracellular protein in the stratum corneum, but as a member of the intermediate filament family of cytoskeletal proteins. Of all such proteins, the keratins are most complex, occurring in two families separable on the basis of size, structure and isoelectric point. The keratin intermediate filaments are heteropolymers of two paired components, one from each family. The pairs of keratins which form the intermediate filaments in basal and differentiated layers of epidermis and other epithelia have been defined and antibodies to specific keratins are now being used for diagnostic purposes. Sophisticated biochemical, physicochemical, and molecular biologic studies have led to complete definitions of almost all the epithelial keratin molecules and to cloning of their genes. These genes are currently being used in analyses of control of keratin expression and definition of the specific abnormalities associated with "keratinopathies" including epidermolysis bullosa simplex and epidermolytic hyperkeratosis.

Avian scale development

Germinative cells of the scutate scale epidermis from 15-day embryos are committed to appendage-specific, beta stratum formation in association with a foreign dermis. Commitment precedes the time (17 days of development) at which beta strata are actually present in their site-specific locations along the outer surface of each scutate scale. This observation suggested the possibility that commitment to beta stratum formation might be occurring as the outer epidermal surface of each scutate scale first becomes established between 12 and 13 days of development. It is at this time that the scale epidermis loses its ability to participate in feather morphogenesis and cell proliferation becomes restricted to a true stratum basale. To examined the ability of the presumptive scutate scale epidermis to generate beta strata in the absence of the inductive scutate scale dermis, scutate scale epidermis from 11-, 12-, and 13-day embryos was recombined with 15-day reticulate scale dermis and grown for 7 or 9 days. The dermis of reticulate scales does not induce beta stratum formation, but it does support differentiation of a beta stratum by the determined 15-day scutate scale epidermis. Using immunohistological and biochemical analyses of beta-keratins, we find that each of these presumptive scutate scale epidermises is competent to generate appendage-specific beta strata in the absence of the scutate scale dermis. This determination is occurring prior to scale ridge morphogenesis and differentiation of the epidermis into the distinct outer and inner epidermal surfaces of the scale ridge. The restricted distribution of beta strata to the apical domes of individual reticulate-like scales demonstrates that the germinative cells of the committed epidermises are responding to patterned cues. This study also suggests that all basal cells of the presumptive scutate scale epidermis are initially endowed with the ability to generate cells that form a beta stratum.

Region-specific expression of scutate scale type beta keratins in the developing chick beak

This study shows that different patterns of scutate scale type beta keratins are accumulated in the three adjacent structures of the embryonic chick beak: periderm, egg tooth, and cornified beak. The cornified beak accumulates all of the beta keratins of scutate scale except pp2,3. The periderm, which is the outermost, multilayered covering of the whole embryonic beak, accumulates only beta keratins 2,3, and p2,3 of the scutate scale pattern. The egg tooth, which is the rounded elevation on the dorsal surface of the upper beak, and the embryonic claw accumulate greatly reduced levels of 2,3 and p2,3 compared to scutate scale. Like cornified beak, the claw does not accumulate pp2,3, but both tissues express a potentially new beta keratin, beta keratin 8. Neither the histidine rich "fast" proteins (HRPs), which are expressed in embryonic scutate scales and feathers, nor the avian cytokeratin associated proteins (cap-1 and cap-2), which are expressed in scutate and reticulate scales, are expressed in any of the embryonic beak structures or in the claw. The implications of these findings with regard to regulation of terminal differentiation of avian skin are discussed.

The structure and expression of a gene encoding chick claw keratin

A cDNA library was constructed from embryonic chick claw mRNA and a claw keratin (cKer)-encoding clone was isolated and sequenced. Subsequently, a genomic clone, containing four cKer-encoding genes (cKer) was isolated and one of the genes (cKer1) was completely sequenced. The cKerl gene appears to be differentially expressed in the keratinizing tissue appendages of the embryonic chick, being abundantly expressed in the claw and at a low level in feather tissue. Comparison of the deduced amino acid (aa) sequence of the cKer to those of feather (fKer) and scale keratins (sKer) showed that the regions conserved between fKer and sKer are also found in the cKer. The glycine-rich as repeat region characteristic of sKer is also present in a shortened form in the cKer sequence. Like the fKer genes (fKer) and the feather histidine-rich protein-encoding gene (HRP), the cKer1 gene also contains one intron which interrupts the 5'-noncoding region at an equivalent position to that found in the fKer and HRP genes. Genomic Southern analysis using the cKer cDNA as a probe indicated the presence of several related genes in the chick genome.

Avian keratin genes. II. Chromosomal arrangement and close linkage of three gene families

We describe the isolation and characterization of a set of overlapping cosmid clones that contain chicken keratin genes. The 100 kb (1 kb = 10(3) base-pairs) of DNA represented in these clones contains a cluster of 18 feather keratin genes spanning 53 kb of DNA. The feather keratin genes are spaced about 3 kb apart and at least 11 of them have the same transcriptional orientation. Southern analysis using oligonucleotide probes made from highly conserved portions of the 5' non-coding, intron and 3' non-coding regions, respectively, indicate that these sequences have been highly conserved among the gene family as a whole, with only one or two exceptions in each case. The presence of some regularly repeated restriction enzyme sites are indicative of tandem duplication events in the recent history of the feather keratin gene family. The feather keratin gene locus is flanked on both sides by related types of keratin genes. On the 5' side of the feather gene cluster are three keratin genes (designated feather-like) that are located 5 kb from the last feather keratin gene and are spaced about 4 kb apart. On the 3' side of the feather gene cluster, 21 kb from the last feather keratin gene, lies a cluster of four genes that encode claw keratins. These genes are spaced about 1 kb apart and appear to be divergently transcribed. Partial DNA sequence analysis of the feather-like gene lying proximal to the feather keratin gene cluster demonstrated that it encodes a protein of 115 amino acid residues that is 80% homologous to the feather keratins at both the DNA and amino acid sequence levels. The feather-like gene(s) are expressed in both embryonic and adult (post-hatch) chick feathers and at a very low level in embryonic scale tissue. These genes therefore form a new family of feather proteins that is distinct from the previously characterized feather keratins.

Avian keratin genes. I. A molecular analysis of the structure and expression of a group of feather keratin genes

The nucleotide sequence of the four complete chicken feather keratin genes A to D contained in the previously isolated recombinant lambda CFK1 has been determined. All four genes have a very similar structure; each gene encodes a polypeptide of 97 amino acid residues and contains an intron in the 5' non-coding region, 37 base-pairs from the cap site. Comparison of the previously determined feather keratin gene C sequence to genes A, B and D indicates that a high level of gene correction has occurred in the protein coding and 5' non-coding regions, which show more than 90% homology, whereas the intron and 3' non-coding regions are by contrast poorly conserved with one or two exceptions. The dramatic conservation of the 5' non-coding region between the feather keratin sequences and an unrelated but co-expressed gene encoding a histidine-rich protein suggests that this segment may play an important role in transcriptional regulation. In addition, both gene types contain an identically positioned intron in the 5' non-coding region. Northern blots performed using gene-specific probes show that the four characterized genes A to D plus gene E, which is partially contained in the recombinant lambda CFK1, are all expressed in feather tissue from 14-day old chick embryos. In addition, we report that a scale keratin gene (originally isolated from a scale complementary DNA library) is expressed at a low level in the embryonic feather.

The amino acid sequence of component 7c, a type II intermediate-filament protein from wool

Component 7c is one of the four homologous type II intermediate-filament proteins that, by association with the complementary type I proteins, form the microfibrils or intermediate filaments in wool. Component 7c was isolated as the S-carboxymethyl derivative from Merino wool and its amino acid sequence was determined by manual and automatic sequencing of peptides produced by chemical and enzymic cleavage reactions. It is an N-terminally blocked molecule of 491 residues and Mr (not including the blocking group) of 55,600; the nature of the blocking group has not been determined. The predicted secondary structure shows that component 7c conforms to the now accepted pattern for intermediate-filament proteins in having a central rod-like region of approximately 310 residues of coiled-coil alpha-helix flanked by non-helical N-and C-terminal regions. The central region is divided by three non-coiled-coil linking segments into four helical segments 1A, 1B, 2A and 2B. The N-and C-terminal non-helical segments are 109 and 71 residues respectively and are rich in cysteine. Details of procedures use in determining the sequence of component 7c have been deposited as a Supplementary Publication SUP 50152 (65 pages) at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1989) 257,5. The information comprises: (1) details of chemical and enzymic methods used for cleavage of component 7c, peptides CN1, CN2 and CN3, and various other peptides, (2) details of the procedures used for the fractionation and purification of peptides from (1), including Figures showing the elution profiles from the chromatographic steps used, (3) details of methods used to determine the C-terminal sequence of peptide CN3, and (4) detailed evidence to justify a number of corrections to the previously published sequence.

An ultra-high sulfur keratin gene is expressed specifically during hair growth

To study the regulation of the hair cycle in the mouse, we have isolated and characterized a gene for ultra high sulfur keratin that is expressed specifically during the active hair growth cycle. The gene (gUHSK-704Eco) was isolated as a member of a gene cluster on a recombinant phage with a DNA insert of 18 kb that was isolated by screening a murine genomic library at low stringency with a synthetic oligonucleotide derived from a sheep high sulfur keratin gene (Powell, Nucleic Acids Res. 1983 11, 5327). The murine ultra-high sulfur keratin gene has no intervening sequence; the 558 nucleotide of the coding region specify 186 amino acids, of which 70 (37%) are cysteine. A Cys-Cys-Gln-Pro repeat is found 12 times within the coding region. RNA dot blots show that the ultra-high sulfur keratin gene is expressed during the hair cycle concomitant with the anterior-posterior temporal pattern of the normal murine hair cycle.

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

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