Developmental expression patterns and association analysis of sheep KAP8.1 and KAP1.3 genes in Chinese Merino sheep

The keratin-associated protein (KAP) is one of the main structural proteins of wool fibre, which is responsible for the major structural and mechanical properties of the wool fibre. Here, the quantitative real-time PCR was used to investigate the developmental changes of KAP8.1 and KAP1.3 mRNA expression levels in skin tissue of Chinese Merino lambs. In addition, the genetic variations of sheep KAP8.1 and KAP1.3 genes and their associations with wool traits were also tested by least square means in 197 adult Chinese Merino sheep. The results showed that the developmental expression patterns of KAP8.1 and KAP1.3 genes were similar, presenting the highest levels at day 0 followed by decline, the sheep KAP1.3 was highly expressed in the skin, while the KAP8.1 was weakly expressed. Moreover, association analysis showed that polymorphisms at both KAP8.1 and KAP1.3 loci were associated with fiber diameter (P = 0.021 and 0.001, respectively). In detail, individuals with KAP8.1 BC genotype were significantly smaller fibre diameter than those of individuals with genotype AB (P<0.01) and BB (P<0.05), individuals with KAP1.3 AA genotype were significantly smaller fibre diameter than those of individuals with genotype AB (P<0.05) and BB (P<0.01). In addition, the combined genotypes of KAP8.1-KAP1.3 genes seem to improve the association, and the optimal combined genotype of KAP8.1-KAP1.3 genes was BC-AA.