Abstract
Cashmere goat skin contains two types of hair follicles (HF): primary hair follicles (PHF) and secondary hair follicles (SHF). Although multiple genetic determinants associated with HF formation have been identified, the molecules that determine the independent morphogenesis of HF in cashmere goats remain elusive. The growth and development of SHF directly influence the quantity and quality of cashmere production. Here, we report the transcriptome profiling analysis of nine skin samples from cashmere goats using 60- and 120-day-old embryos (E60 and E120, respectively), as well as newborns (NB), through RNA-sequencing (RNA-seq). HF morphological changes indicated that PHF were initiated at E60, with maturation from E120, while differentiation of SHF was identified at E120 until formation of cashmere occurred after birth (NB). The RNA-sequencing analysis generated over 20.6 million clean reads from each mRNA library. The number of differentially expressed genes (DEGs) in E60 vs. E120, E120 vs. NB, and E60 vs. NB were 1,024, 0 and 1,801, respectively, indicating that no significant differences were found at transcriptomic levels between E120 and NB. Key genes including B4GALT4, TNC, a-integrin, and FGFR1, were up-regulated and expressed in HF initiation from E60 to E120, while regulatory genes such as GPRC5D, PAD3, HOXC13, PRR9, VSIG8, LRRC15, LHX2, MSX-2, and FOXN1 were up-regulated and expressed in HF keratinisation and hair shaft differentiation from E120 and NB to E60. Several genes belonging to the KRT and KRTAP gene families were detected throughout the three HF developmental stages. The transcriptional trajectory analyses of all DEGs indicated that immune privilege, glycosaminoglycan biosynthesis, extracellular matrix receptor interaction, and growth factor receptors all played dominant roles in the epithelial-mesenchymal interface and HF formation. We found that the Wnt, transforming growth factor-beta/bone morphogenetic protein, and Notch family members played vital roles in HF differentiation and maturation. The DEGs we found could be attributed to the generation and development of HF, and thus will be critically important for improving the quantity and quality of fleece production in animals for fibres.
Highlights
Cashmere goats have double coats consisting of non-modulated fine inner hairs or cashmere fibres produced by secondary hair follicles (SHF) and guard hairs produced by primary hair follicles (PHF), which are invaginated into the basement membrane of the skin [1, 2]
The time point and characteristics of HF morphogenesis during embryogenesis in cashmere goats has been reported to be between 55 and 135 days of fetal life, and this process is divided into three specific stages: initiation, differentiation and maturation [7]
Our analysis identified a set of genes belonging to keratin family member encoding genes (KRT) and keratin-associated protein encoding genes (KRTAP), which were markedly up-regulated in E120 vs. E60
Summary
Cashmere goats have double coats consisting of non-modulated fine inner hairs or cashmere fibres produced by secondary hair follicles (SHF) and guard hairs produced by primary hair follicles (PHF), which are invaginated into the basement membrane of the skin (epithelial and mesenchymal compartment) [1, 2]. Cashmere is a fine wool cashmere fibre (generally with diameter < 19 μm) that is used to produce soft luxurious apparel. Given that the generation of HF is established during early fetal life, and fibre characteristics are realised when the follicles are mature, examination of the processes and transcriptional regulatory mechanisms of the skin epithelium and skin appendage morphogenesis is required to achieve maximum cashmere production [4]. The process of follicle morphogenesis has been studied extensively in murine models, but rarely in goats that produce fibres [5, 6]. HF morphogenesis is a continuum process between 55 and 135 days of fetal life, which can represent the initiation, differentiation and maturation stages of HF
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