Significance of KLK7 expression, polymorphisms, and function in sheep horn growth

Sheep horns play a critical role in the survival and reproduction of sheep. Research on sheep horns not only aids in comprehending their biological roles but is also vital for developing hornless breeds. Although previous studies have suggested that KLK7 may be associated with keratin growth, there are few studies that have focused on the role of KLK7 in sheep horns. This study aims to elucidate the relationship between KLK7 and sheep horns by analyzing the expression, genetic polymorphisms, and potential functions of KLK7 in sheep horns. This study utilized RNA sequencing (RNA-Seq) data to analyze the expression levels of the KLK7 gene across different species, as well as among different breeds, tissue types, and genders in sheep. Potential functional sites of KLK7 were explored using whole-genome sequencing (WGS) data. Allele specific expression sites in the KLK7 gene sequence were identified. Finally, the WGS data were linked with sheep horn length for association analysis, and significantly different single-nucleotide polymorphisms (SNPs) were detected and validated by Kompetitive Allele Specific PCR (KASP) genotyping. Our results demonstrate that KLK7 was highly expressed in soft horn and skin tissues, and its expression was significantly higher in small-horned sheep than it was in large-horned sheep, suggesting that KLK7 may have an inhibitory effect on horn growth. By comparing the amino acid sequence of KLK7 with KLK7 sequences in other species, we discovered eight amino acids at specific positions in the KLK7 protein sequence that may have regulatory functions in determining the size of horns in ruminant animals. Thirteen SNPs with F-statistic value (Fst) > 0.15 were identified. By integrating RNA-Seq and WGS data, we discovered two SNPs (g.56695395 T > C and g.56695484A > C) with allele specific expression between the large- and small-horned sheep. The two SNPs were validated and were found to have significantly different (P