Short communicationVariation in the KAP6-1 gene in Chinese Tan sheep and associations with variation in wool traits
Introduction
The keratin associated proteins (KAPs) are a structural component of wool fibres and form a matrix that cross-links with the intermediate filaments (Powell and Rogers, 1997). KAPs can be classified into three broad groups on the basis of their amino acid composition: the high glycine-tyrosine (HGT; 35–60 mol% glycine and tyrosine) KAPs, the high sulphur (HS; ≤30 mol% cysteine) KAPs and the ultra-high sulphur (UHS; >30 mol% cysteine) KAPs (Gong et al., 2016). Of these, the HGT-KAPs are predominantly found in the orthocortex of wool fibres and they vary in abundance both between and within breeds (Rogers, 2006, Gillespie, 1990). For example, wool from Lincoln sheep contains less than 1% by weight HGT-KAPs, while Merino wool has between 4% and 12% of HGT-KAPs by weight (Gillespie, 1990). Merino felting lustre (FL) mutant wool contains a low amount of HGT-KAPs (Gillespie and Darskus, 1971), and the expression of the HGT-KAP genes has been revealed to be down-regulated in FL mutant follicles (Li et al., 2009). This variation in the content of HGT-KAPs in wool fibres raises the question of whether these proteins affect the properties of wool.
Three HGT-KAP families have been identified in sheep: KAP6, KAP7 and KAP8 (Gong et al., 2016). KAP6 is a diverse KAP family with five genes identified to date (Zhou et al., 2016). Recently variation in one KAP6 gene (KRATP6-1) has been reported to affect wool fibre diameter-associated traits (Zhou et al., 2015).
Tan sheep are indigenous to China and they are recognised for producing long, curled or crimped, white wool by the early age of approximately 35 days. This is known as the age of “Er-mao” by Chinese people. Four wool crimp patterns have been described for wool at ‘Er-mao”, and these can be translated into “random curly”, “soft and big curly”, “walnut flower curly” and “Chinese string curly” (Tao et al., 2017). Variation in these traits affects the value of wool and lamb pelts in China. The genetic basis of these characteristics is currently unknown, hence the objective of this study was to characterize KRTAP6-1 in Chinese Tan sheep and investigate whether variation if present in the gene, affects wool traits of economic value in China.
Section snippets
Sheep investigated and wool traits recorded
Five hundred and twenty-nine Chinese Tan lambs from 23 sire-lines were investigated. The majority of the lambs were born as singles and only 14 of them were born as twins. These twins were removed from the association analyses and only the 515 single lambs were analysed.
As most rural Chinese wool and pelt producers do not have access to internationally standardised wool testing methods, they have devised and used their own methods to measure the wool traits that they are interested in and
Polymorphism of KRTAP6-1 in Chinese Tan sheep
SSCP analysis of PCR amplicons identified four alleles of KRTAP6-1 in the Chinese Tan sheep, including two previously identified variants (A and B) and two new variants (D and E) that have not been described previously (Fig. 1). Variant C (Zhou et al., 2015) was not found in these Tan sheep. Variant E was defined by a SNP that has not previously been described and was located upstream of the coding region. While variant D did not contain any new SNP, it had a sequence difference that appears to
Discussion
The identification of two additional variants of this gene takes the reported number of KRTAP6-1 variants from three to five, suggesting KRTAP6-1 is a polymorphic gene in sheep and confirming its effect on wool characteristics warrants further investigation.
Associations were revealed between variation in KRTAP6-1 and various wool traits of value in Chinese markets. At Er-mao, a longer straightened fibre-length, a higher crimp number and a higher degree of crimping were found to be associated
Conflict of interest statement
The authors have declared that no conflict of interest exists.
Acknowledgments
The financial support from the Lincoln University Gene-Marker Laboratory and the Ningxia Special Breeding Program are acknowledged. We thank the support of the AGMARDT Postdoctoral Fellowship to Hua Gong, and the technical support from Seung Byun and Qian Fang.
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2019, Molecular Phylogenetics and EvolutionCitation Excerpt :The KRTAPs are intron-less genes, with small coding sequences of less than 1 kb in length) (Rogers and Schweizer, 2005; Gong et al., 2016; Stein, 2004; Torrents et al., 2003). In addition, the KRTAPs show high levels of population variation, with all known KRTAP genes being polymorphic in sheep (Gong et al., 2016, 2010b; Zhou et al., 2016), where they are well studied because of their roles in determining wool phenotypes (Li et al., 2017a, 2017b, 2017c; Tao et al., 2017a, 2017b; Zhou et al., 2015). Despite this variation, it has been reported that some KRTAP genes show a pattern of concerted evolution between the paralogous gene copies (Khan et al., 2014; Rogers et al., 1994; Wu et al., 2008).
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