Search for Variation in the Ovine KAP7-1 and KAP8-1 Genes Using Polymerase Chain Reaction–Single-Stranded Conformational Polymorphism Screening

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 While use of these natural fibres has in some respects been superseded by the use of synthetic and plant-based fibres, increased accounting for the carbon and water footprint of these fibres is creating a re-emergence of interest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.

Variation in ovine KRTAP8-1 affects mean staple length and opacity of wool fiber

In this study, keratin-associated proteins gene (KRTAP8-1) from five different sheep breeds and breed-crosses (n = 310) was genotyped using a Polymerase Chain Reaction-Single Strand confirmation Polymorphism (PCR-SSCP). Six unique genotypes were observed: AA, AC, AD, AE, DD and EE, with AA being the most common in the different breeds and crosses. Twelve wool characteristics: yield, mean staple length (MSL), bulk, mean fiber diameter (MFD), fiber diameter standard deviation (FDSD), coefficient of variation of fiber diameter (CVFD), medullation, standard deviation of medullation (MeSD), coefficient of variation of medullation (CVMed), opacity, standard deviation of opacity (OpSD), and coefficient of variation of opacity (CVOp) were measured on wool derived from the sheep. Variation in KRTAP8-1 was found to have strong association with MSL, OpSD and CVOp (p ≤ 0.027). The MSL of sheep of genotype AE was greater (p = 0.027) than for sheep of genotype AA. The OpSD of sheep of genotype AA was less (p = 0.017) than sheep with the AE genotype, and the CVOp of sheep with genotype AA was less (p = 0.018) than sheep with genotype AE. Further studies are required to confirm the role of variation in KRTAP8-1 in improving quality wool production.

Polymorphism in the ovine keratin-associated protein gene KRTAP7-1 and its association with wool characteristics

The keratin-associated proteins (KAPs) are structural components of wool fibers and variation in the genes encoding the KAPs can affect wool traits. In this study, sequence variation in the ovine KAP7-1 gene (KRTAP7-1) was investigated in 222 sheep across 5 different Pakistani breeds and breed crosses. Two previously identified variants (A and B) of the KRTAP7-1 coding sequence were identified. The frequency of the genotypes AA and AB was 76% and 23%, respectively, and that of BB was 1%. The association of sequence variation with various wool traits and measurements included yield (the proportion of greasy fleece weight that is clean fleece), mean staple length (MSL), wool bulk, mean fiber diameter, fiber diameter SD, the coefficient of variation of fiber diameter, medullation, the SD of medullation, the coefficient of variation of medullation, fiber opacity, the SD of opacity, and the coefficient of variation of opacity. Variation in KRTAP7-1 was found to be associated with yield (P = 0.017). The adjusted mean yield of sheep of genotype AA (n = 169) was 79.9 ± 2.72%, while that of genotype AB (n = 51) was 81.9 ± 3.37%. There was also an association between variation in KRTAP7-1 and MSL (P = 0.024), with sheep of genotype AA (n = 169) having an adjusted mean MSL of 47.3 ± 0.57 mm compared with sheep of genotype AB (n = 51, 50.9 ± 0.65 mm). Yield and MSL are both important wool production traits, hence variation in KRTAP7-1 needs to be further investigated in more sheep of differing breed.

Characterisation of an Ovine Keratin Associated Protein (KAP) Gene, Which Would Produce a Protein Rich in Glycine and Tyrosine, but Lacking in Cysteine

The keratin-associated proteins (KAPs) are structural components of hair/wool fibres. All of the KAPs identified to date contain cysteine, which is thought to form disulphide bonds cross-linking the keratin intermediate filaments. Here, we report the identification of a KAP gene in sheep that would produce a protein that contains a high proportion (63.2 mol%) of glycine and tyrosine, but would not contain any cysteine. This suggests that other forms of intra- and inter-strand interaction may occur with this KAP, such as interactions via ring-stacking and hydrogen-bonding. The gene was dissimilar to any previously reported KAP gene, and was therefore assigned to a new family, and named KRTAP36-1. The KRTAP36-1 genome sequence was almost identical to some EST sequences from sheep and goat skin follicles, suggesting that it is present and expressed in sheep and goats. A BLAST search of the human genome assembly sequence did not reveal any human homologue. Three variant sequences (named A to C) of ovine KRTAP36-1 were identified and four single nucleotide polymorphisms (SNPs) were detected. One SNP was located 32 bp upstream of the coding region, and all of the others were in the coding region and were nonsynonymous. After correcting for potential linkage to the proximal KRTAP20-1, variant B of KRTAP36-1 was found to be associated with increased prickle factor (PF) in wool, suggesting that variation in the gene may have the potential to be used as gene marker for breeding sheep with lower PF.

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.

Identification of Ovine KRTAP28-1 and Its Association with Wool Fibre Diameter

Simple Summary

Keratin-associated proteins (KAPs) are fundamental components of wool and hair fibres. They are split into three broad groups: the high sulphur (HS), the ultra-high sulphur (UHS) and the high glycine-tyrosine (HGT) KAPs. KRTAP25-1 encodes a HS-KAP protein and the gene has recently been identified in humans. Here, we report the absence of a KRTAP25-1 in sheep, and we describe a new HS-KRTAP (named KRTAP28-1) in the chromosome region where KRTAP25-1 was expected to be found. Six variants (A−F) of KRTAP28-1 containing eight single nucleotide polymorphisms (SNPs) and a TG dinucleotide repeat polymorphism were detected. One SNP was located upstream of the start codon and all the others were non-synonymous SNPs, including a nonsense SNP. The TG repeat polymorphism would lead to a reading frame shift at the carboxyl-terminal end. The association of KRTAP28-1 with wool traits was investigated with 383 Southdown × Merino-cross lambs from seven sire lines. Of the four genotypes with a frequency over 5%, lambs of genotypes AB and BD produced wool of a smaller mean fibre diameter (MFD) than lambs of genotype BC. This shows that KRTAP28-1 is associated with a key wool trait, and variation in this gene might therefore have value as a marker for improving that trait.

Abstract

Keratin-associated proteins (KAPs) are a diverse group of proteins and form a matrix that cross-links keratin intermediate filaments in hair and wool fibres. From over 100 KAP genes (KRTAPs) identified in mammalian species, KRTAP25-1 is a high sulphur (HS)-KAP gene, which has recently been described in humans. Here, we report the absence of KRTAP25-1 in sheep, and describe a new HS-KRTAP (named KRTAP28-1) in the chromosome region where KRTAP25-1 was expected to be found. Six variants (A−F) of KRTAP28-1 containing eight single nucleotide polymorphisms (SNPs) and a TG repeat polymorphism were detected. One was positioned 30 bp upstream of the transcription start codon and all the others were non-synonymous SNPs, including a nonsense SNP. The TG repeat polymorphism would lead to a reading frame shift at the carboxyl-terminal end. The effect of KRTAP28-1 on wool traits was investigated with 383 Southdown × Merino-cross lambs from seven sire lines. Of the four genotypes with a frequency of over 5%, lambs of genotypes AB and BD produced wool of a smaller MFD than lambs of genotype BC. This shows that KRTAP28-1 is associated with wool fibre diameter, and that variation in this gene might have potential for use as a gene marker for reducing wool fibre diameter.

Polymorphism of keratin-associated protein (KAP) 7 gene and its association with wool traits in Rambouillet sheep

In the present study, association of polymorphic variants of KAP 7 gene with wool traits in Rambouillet sheep was investigated by using SSCP-PCR. Genomic DNA was isolated from blood samples of 100 Rambouillet sheep. A 388 bp segment was amplified by PCR using ovine specific primers for KAP 7 gene. The results identified 3 genotypes, viz. AA, AB and BB with genotype frequencies of 0.340 (34), 0.270 (27) and 0.390 (39) respectively and allele frequencies of 0.475 for allele A and 0.525 for allele B. The χ²-test showed that the genotype distribution was not in agreement with Hardy-Weinberg equilibrium (HWE). KAP 7 gene has significantly higher clean wool yield and greasy fleece weight in males whereas females have significantly superior fibre diameter, higher staple length and wool count. BB genotype has significantly higher staple length followed by AA and AB genotype. BB genotype has significantly higher greasy fleece weight production followed by AB and least by AA genotype. From the study, it may be concluded that KAP 7 gene might be a potential molecular marker for genetic selection for higher staple length and greasy fleece weight in Rambouillet sheep.

Variation in the Ovine KAP6-3 Gene (KRTAP6-3) Is Associated with Variation in Mean Fibre Diameter-Associated Wool Traits

Polymerase chain reaction-single stranded conformational polymorphism (PCR-SSCP) analysis was used to investigate variation in the ovine KAP6-3 gene (KRTAP6-3) in 383 Merino × Southdown-cross lambs from four sire-lines, and to determine whether this variation affects wool traits. Five PCR-SSCP banding patterns, representing five different nucleotide sequences, were detected, including four previously identified (named A, B, C, and F) variants and one newly identified (named G) variant. A new non-synonymous single nucleotide polymorphism (SNP) and a 45-bp deletion were detected in variant G. Of the three common genotypes (AA, AB, and AG) identified in these sheep, wool from sheep that were AG, on average, had a lower mean fibre diameter (MFD), fibre diameter standard deviation (FDSD), and prickle factor (PF) than wool from AA sheep, whereas wool from AB sheep, on average, had a higher MFD, FDSD, and PF than wool from AA sheep. This suggests that variation in ovine KRTAP6-3 affect MFD, FDSD, and PF, and that this gene may have potential for use as a gene-maker for improving fibre diameter-associated wool traits.

Identification of the Ovine Keratin-Associated Protein 22-1 (KAP22-1) Gene and Its Effect on Wool Traits

Keratin-associated proteins (KAPs) are structural components of wool and hair fibers. To date, eight high glycine/tyrosine KAP (HGT-KAP) families have been identified in humans, but only three have been identified in sheep. In this study, the putative ovine homolog of the human KAP22-1 gene (KRTAP22-1) was amplified using primers designed based on a human KRTAP22-1 sequence. Polymerase chain reaction-single stranded conformational polymorphism (PCR-SSCP) was used to screen for variation in KRTAP22-1 in 390 Merino × Southdown-cross lambs and 75 New Zealand (NZ) Romney sheep. Three PCR-SSCP banding patterns were detected and DNA sequencing revealed that the banding patterns represented three different nucleotide sequences (A-C). Two single nucleotide polymorphisms (SNPs) were identified in these sequences. Variant B was most common with a frequency of 81.3% in NZ Romney sheep, while in the Merino × Southdown-cross lambs, A was more common with a frequency of 51.8%. The presence of B was found to be associated with increased wool yield and decreased mean fiber curvature (MFC). Sheep of genotype BB or AB had a higher wool yield than those of genotype AA. These results suggest that ovine KRTAP22-1 variation may be useful when developing breeding programs based on increasing wool yield, or decreasing wool curvature.

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.

Combining Untargeted and Targeted Proteomic Strategies for Discrimination and Quantification of Cashmere Fibers

Cashmere is regarded as a specialty and luxury fiber due to its scarcity and high economic value. For fiber quality assessment, it is technically very challenging to distinguish and quantify the cashmere fiber from yak or wool fibers because of their highly similar physical appearance and substantial protein sequence homology. To address this issue, we propose a workflow combining untargeted and targeted proteomics strategies for selecting, verifying and quantifying biomarkers for cashmere textile authentication. Untargeted proteomic surveys were first applied to identify 174, 157, and 156 proteins from cashmere, wool and yak fibers, respectively. After marker selection at different levels, peptides turned out to afford much higher selectivity than proteins for fiber species discrimination. Subsequently, parallel reaction monitoring (PRM) methods were developed for ten selected peptide markers. The PRM-based targeted analysis of peptide markers enabled accurate determination of fiber species and cashmere percentages in different fiber mixtures. Furthermore, collective use of these peptide makers allowed us to discriminate and quantify cashmere fibers in commercial finished fabrics that have undergone heavy chemical treatments. Cashmere proportion measurement in fabric samples using our proteomic approach was in good agreement with results from traditional light microscopy, yet our method can be more readily standardized to become an objective and robust assay for assessing authenticity of fibers and textiles. We anticipate that the proteomic strategies presented in our study could be further implicated in discovery of quality trait markers for other products containing highly homologous proteomes.

The sheep KAP8-2 gene, a new KAP8 family member that is absent in humans

The keratin-associated proteins (KAPs) are fundamental components of hair and wool fibres, and are believed to in part be responsible for some of the properties of these fibres. KAPs can be divided into three groups: the high sulphur (HS) KAPs, the ultra-high sulphur (UHS) KAPs and the high glycine-tyrosine (HGT) KAPs. KAP8 is a HGT-KAP family and was believed to be coded for by a single gene in both humans and sheep. However, the recent identification of a KAP8-2 gene in goats led us to investigate whether a KAP8-2 gene exists in sheep. A BLAST search of the Ovine Genome Assembly v2.0 using the coding sequence of caprine KRTAP8-2 identified a homologous region on sheep chromosome 1 (OAR1:123005473_123005664; E = e(-101)). This region was clustered with a number of previously identified KAP genes including (in order from the centromere) KRTAP11-1, KRTAP7-1, KRTAP8-1, KRTAP6-2, KRTAP6-1, KRTAP13-3 and KRTAP24-1. PCR-SSCP analysis of the notional gene revealed two dissimilar PCR-SSCP banding patterns, representing two DNA sequences. A single nucleotide difference 21 bp upstream of the TATA box was identified. The two sequences did not have great homology with known ovine KRTAP sequences, but high sequence identity was found with KRTAP8-2 from goats and reindeer. These results suggest that sheep possess a KAP8-2 gene and that this gene is polymorphic. The notional KAP8-2 protein is comprised of 63 amino acid residues and is rich in glycine and tyrosine, but has a low cysteine content. In contrast to other HGT-KAPs, ovine KAP8-2 contains more acidic amino acid residues, and this would likely result in a lower isoelectric point (pI) of 6.3.

Variation and expression of KAP9.2 gene affecting cashmere trait in goats

Keratin-associated proteins 9.2 (KAP9.2) gene encodes one of the ultra high sulfur KAPs. Variation in KAP genes may affect the structure of KAPs and hence cashmere characteristics. In order to test the association between the polymorphism of KAP9.2 gene and cashmere trait, DNA sequencing was used to detect a novel C/T polymorphism of KAP9.2 gene from a genomic DNA pool. The mutation could be recognized by Pst I restriction enzyme. To Shanbei white cashmere goat, Inner Mongolia white cashmere goat and Guanzhong dairy goat, the genotypic frequencies of TT, TC and CC from total 1,236 animals were as follows: 0.047, 0.519 and 0.434; 0.180, 0.592 and 0.228; 0.431, 0.544 and 0.025. The allelic frequencies of T and C were 0.307 and 0.693; 0.476 and 0.524; 0.703 and 0.297, respectively, in breeds mentioned above. The frequency of C allele between cashmere and dairy goat was significant (P < 0.01). To provide support for the hypothesis that SNP 586 was responsible for KAP9.2 expression, quantitative real-time PCR analysis revealed that the expression level of KAP9.2 was reduced in individuals bearing genotype CC compared with TT individuals, suggesting that C was the nucleotide causing decreased expression of KAP9.2 or was in linkage disequilibrium with the causative SNP. The 586C/T SNP found in this study might control translation or stability of KAP9.2 mRNA, which would be beneficial for marker assistant selection in cashmere goat breeding.

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.