Regulatory Mechanism Of Morphogenesis And Development Of Sheepskin Wool Follicles And Sebaceous Glands

Wool of sheep has good economic value,and developmental morphology of wool follicles can determine wool quality in many aspects.Sebaceous glands,derived from wool follicles,secret sebum that not only nourish and protect grease wool,but also produce lanolin.Tibetan sheep is a unique breed of coarse wool sheep in China,but there are few studies on the development of wool follicles or sebaceous glands of coarse wool breeds.It is necessary to understand the morphogenesis of wool follicles and sebaceous glands,as well as the expression patterns of key signals related to the process.The wool traits of different body regions of Tibetan sheep,and also diverse from fine and coarse wool breeds.Morphologic and molecular studies of body regions and coarse to fine wool breeds may provide a theoretical basis for sheep breeding,especially for wool fineness,net hair rate and lanolin production.In this study,sections with HE staining and Oil-Red staining were performed on Tibetan sheep fetuses’skin throughout different stages,as well as immunohistochemical（fluorescence）localization and q RT-PCR quantification of marker signals at different developmental stages,to detail the morphological and molecular marker characteristics at each stage during development.Morphologic differences between dorsal to belly skin of Tibetan lamb or between Tibetan sheep to Qinghai fine wool sheep at same period were compared.Different signaling networks were described based on transcriptional sequencing analysis.Whole genome sequencing data of plateau Tibetan sheep and several fine wool breeds in database were used for differential selection signal analysis by F_ST,XP-EHH and i HS,and the single nucleotide polymorphism that might be related to wool fineness or sebaceous gland morphology were screened.The results were as follows.1.In Tibetan sheepskin,the morphologic development of wool follicles experienced 6stages,with marker genes located in specific region and related transcriptional level changes.The stages were Placodes,Pc/DC,Germ,Peg,Bulbous peg,and Follicle,successively.Genes induced wool follicles proliferation and differentiation were highly expressed before Peg which expressed in almost all hair follicle structures,then,decreased.Instead,genes for sebaceous glands development climbed fast after the very first sebocyte emerged,and were specifically located in sebaceous glands.2.The relative size of sebaceous glands in Tibetan sheep dorsal skin were significant smaller than that in belly;and in Qinghai fine wool sheep dorsal skin.RNA-seq analysis between dorsal to belly skin of Tibetan lamb,and between Tibetan or Small Tailed Han sheep to Chinese super merino showed in same trends:different expressional genes were enriched to PI3κ-Akt,Wnt,TNF KEGG pathways;GO Terms was enriched in biological processes such as fatty acid biosynthesis and fatty acid chain elongation.Screening of differential alternative splicing events of Tibetan sheep dorsal and belly skin RNA-seq data,skipped exon of the 7th exon of FBXO32 in belly skin tissue resulting in partial deletion of its F-box domain and decreased negative regulation of c-Myc,which was related to larger sebaceous glands in belly skin compared to dorsal.3.The nucleotide polymorphisms of Tibetan sheep are more abundant than those of fine wool sheep,and many sites of fine wool sheep are close to homozygous after breeding.A total of 62111 SNPs and 1705 genes were identified by whole genome sequencing analysis of Tibetan sheep and fine wool sheep.The Thr165Ile missense mutation in EVI2B coding region was screened.Verification in Tibetan sheep and Qinghai fine wool sheep in this study.In summary,WFs were completely developed with appendages before birth.In early stages,progenitor cell proliferated and differentiated to induct WFs formation,and in later period,appendages budded,grew and developed to improve physiological function.Morphology related to signaling network patten presented regularity:thicker wool with smaller sebaceous glands in（dorsal）region or（coarse wool）breeds,the molecular network tended to promote development of wool follicles.Reasons result in larger sebaceous glands might be:higher frequency of 7th exon skipped of FBXO32 in belly Tibetan sheepskin,or EVI2B Thr165Ile missense variant was strongly selected in fine-wool sheep.