Transcriptomic Identification and Validation of FGF5/FGF18 Associated with Cashmere Fiber Fineness in Yanshan Cashmere Goats

This study aims to accelerate the breeding of Yanshan cashmere goats and explore key genes affecting the cashmere fiber fineness. In this study, two groups of 5 individuals with significant differences in cashmere fiber fineness (coarse-cashmere group and fine-cashmere group) were selected from 101 female Yanshan cashmere goats. Using RNA-seq technology, transcriptome sequencing was performed on the skin tissues of the two groups of goats. Candidate genes with significant differential expression and closely related to fineness of cashmere fibers were verified using RT-qPCR technology. Screening was performed according to the criteria of |Log2 (fold change)| > 1, P-value < 0.05, padj < 0.05. RNA-seq identified 167 significantly differentially expressed genes, with 135 upregulated and 32 downregulated. Significantly differentially expressed genes were analyzed by GO functional annotation and KEGG pathway enrichment analysis, it was found that FGF5 and FGF18 genes were present in multiple pathways such as fibroblast growth factor receptor signaling pathway, response to fibroblast growth factor, growth factor activity and receptor binding in GO functional annotation. The KEGG pathway enrichment mainly includes MAPK signaling pathway, PI3K Akt signaling pathway, Rap1 signaling pathway, etc. This suggests that these two genes may regulate the cashmere fiber fineness through fibroblast growth. RT-qPCR verification indicated that the mRNA expression levels of both FGF5 and FGF18 genes were lower in the fine-cashmere group compared to the coarse-cashmere group, with a particularly significant difference in mRNA expression levels between the two groups for the FGF18 gene (P < 0.05). The results of RT-qPCR and RNA-seq for the two genes were basically consistent. It is speculated that both FGF5 and FGF18 are key genes regulating the fineness of cashmere fibers in Yanshan Cashmere goats. The research results have enriched our understanding of the molecular genetic mechanisms of cashmere fiber fineness, providing a new theoretical basis for improving the fiber fineness of Yanshan cashmere goats and facilitating the breeding of high-quality individuals.