Ovine KRT81 Variants and Their Influence on Selected Wool Traits of Commercial Value.

Keratins are the main structural protein components of wool fibres, and variation in them and their genes (KRTs) is thought to influence wool structure and characteristics. The PCR-single strand conformation polymorphism technique has been used previously to investigate genetic variation in selected coding and intron regions of the type II sheep keratin gene KRT81, but no variation was identified. In this study, we used the same technique to explore the 5' untranslated region of KRT81 and detected three sequence variants (A, B and C) that contain four single nucleotide polymorphisms. Among the 389 Merino × Southdown cross sheep investigated, variant B was linked to a reduction in clean fleece weight, while C was associated with an increase in both greasy fleece weight and clean fleece weight. No discernible effects on staple length or mean-fibre-diameter-related traits were observed. These findings suggest that variation in ovine KRT81 might influence wool growth by changing the density of wool follicles in the skin, the density of individual fibres, or the area of the skin producing fibre, as opposed to changing the rate of extrusion of fibres or their diameter.

Ovine KRTAP36-2: A New Keratin-Associated Protein Gene Related to Variation in Wool Yield.

Keratin-associated proteins (KAPs) are structural components of wool fibres. High-glycine/tyrosine (HGT)-KAPs are a subset of the KAP family, and their abundance in fibres varies. In this study, we report the discovery of an ovine HGT-KAP gene to which we assigned the name KRTAP36-2. Polymerase chain reaction and single-strand conformation polymorphism (PCR-SSCP) analyses revealed four variants of this gene in a screening population of 170 sheep from a variety of breeds. The DNA sequencing of the variants revealed four single-nucleotide polymorphisms (SNPs) and a dinucleotide deletion. Three of these SNPs were in the coding region, and one of these was non-synonymous and potentially led to the amino acid substitution p.Cys27Gly near the middle of the protein. The remaining SNP was located near the putative TATA box, and the di-nucleotide deletion was near the putative transcription initiation site. The effect of this variation in KRTAP36-2 was investigated in 274 Southdown × Merino lambs that were the progeny of five sires. Variation was only found to be associated with wool yield, that is, the proportion of the greasy fleece that remained as clean fleece upon scouring (expressed as a percentage). This may have some value in increasing wool production.

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

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.

Associations between variation in the ovine high glycine-tyrosine keratin-associated protein gene KRTAP20-1 and wool traits.

The keratin-associated proteins (KAPs) are important constituents of wool fibers. Of the many mammalian KAP genes (KRTAPs) identified, KRTAP20-1 has been described in humans, but it has not been described in any other species. A search of the sheep genome using the human KRTAP20-1 sequence revealed a homologous open reading frame on chromosome 1, which would encode a high glycine-tyrosine KAP. PCR-single-stranded conformational polymorphism (PCR-SSCP) analysis identified 8 different banding patterns representing 8 unique DNA sequences (named A to H). The sequences had highest similarity to the human KRTAP20-1 sequence, and this suggests that they are variants of ovine KRTAP20-1. Among these variants, a 12-bp insertion/deletion and 6 single nucleotide poly- morphisms (SNPs), including one 5' untranslated region (UTR) SNP, one 3' UTR SNP, and 2 nonsynonymous SNPs, were detected. Variant A was found to be associated with a decrease in mean fiber diameter, fiber diameter standard deviation, and prickle factor, whereas variant C was associated with increased greasy fleece weight and decreased wool yield. These associations persisted after adjusting for the effect of 2 nearby KRTAPs (KRTAP6-3 and KRTAP22-1) that have also been reported to associate with these wool traits. This suggests that variation in KRTAP20-1 affects wool yield and mean fiber diameter-associated traits, and that this effect is unlikely to be the result of the clustering of these KRTAPs on chromosome 1.