Variation in the Caprine KAP24-1 Gene Affects Cashmere Fibre Diameter

The keratin-associated proteins (KAPs) are structural components of cashmere fibres. The gene encoding the high-sulphur (HS)-KAP24-1 (KRTAP24-1) has been identified in humans and sheep, but it has not been described in goats. In this study, we report the identification of caprine KRTAP24-1, describe variation in this gene, and investigate the effect of this variation on cashmere traits. A search for sequences orthologous to the ovine gene in the goat genome revealed a 774 bp open reading frame on chromosome 1, which could encode an HS-KAP. Based on this goat genome sequence and comparison with ovine KRTAP24-1 sequences, polymerase chain reaction (PCR) primers were designed to amplify an 856 bp fragment that would contain the entire coding region of the putative caprine KRTAP24-1. Use of this PCR amplification with subsequent single-strand conformation polymorphism (SSCP) analysis of the amplicons identified four distinct patterns of DNA bands on gel electrophoresis, with these representing four different DNA sequences (A to D), in 340 Longdong cashmere goats reared in China. The variant sequences had the highest similarity to KRTAP24-1 sequences from sheep and humans, suggesting that they are variants of caprine KRTAP24-1. Nine single-nucleotide polymorphisms (SNPs) were detected in the gene, including four non-synonymous SNPs and an SNP in proximity to the ATG start codon. Of the three common genotypes (AA, AB, and BB) found in these Longdong cashmere goats, cashmere fibres from goats of genotype AA had lower mean fibre diameter (MFD) than did those of genotype AB, and cashmere fibres from goats of genotype AB had lower MFD than did those from goats of genotype BB.