Comparative Study On Sheep Skin Transcriptome To Reveal Primary Wool Follicle Development Between Coarse And Fine Wool Sheep

Wool,an economic product of wool sheep,is a part of wool follicles in sheep skin.Wool quality is a main characteristic among different breeds in wool sheep husbandry.Coarse and fine wool sheep,have significant differences in thickness and length of the wool fibers.The most obvious difference is outer wool fibers stretching from the development of primary follicles.The relative comparative study is rarely reported.The study on molecular regulatory networks of primary wool follicle development between coarse and fine wool sheep remains unknown.The current study is to conduct comparative studies on the mechanisms regulating early development of skin and wool follicles to explain the differences observed in wool quality and will have impact on improving wool quality for wool sheep breeding.In the present study,the morphological development of primary wool follicles at the specific developmental stage of sheep embryos(about 65 days in embryonic stage,also called the primary wool follicle placode stage)was selected.RNA-seq technique was used for transcriptomes analysis comparison of the dorsal skin samples of the coarse wool and fine wool sheep embryos.The results are as follows:1.In the early development of primary wool follicles,there are morphological differences between the coarse and fine wool sheep skin.A comparative study of skin morphological differences during primary follicle morphogenesis at primary follicle placode stage revealed that the dermis thickness and the cross-sectional area of coarse wool follicle placodes were significantly larger than those of fine wool sheep.2.Comparative study on the molecular mechanisms of skin morphology differences between primary wool follicles of coarse and fine wool sheep.(1)The transcriptional differences between the fetal skin of coarse and fine wool sheep were compared,and detected 726 differentially expressed genes,by RNA-seq sequencing.Among them,there were 435 up-regulated genes and 291 down-regulated genes in the coarse wool sheep samples.(2)GO analyses revealed 498 genes that were enriched in the biological processes,cellular components and molecular functions,and were mainly related to morphogenesis,organ tissue development,and cell differentiation.The KEGG pathway analyses indicate that the differentially expressed genes were mainly related to signaling pathways regulating cell morphology,cell development and proliferation,such as "PI3K-Akt signaling pathway","MAPK signaling pathway","Focal adhesion","ECM-receptor interaction",and "Wnt signaling pathway".(3)Further analyses detected 4,31 and 12 differentially expressed genes,corresponding to the development of the epidermis,dermis and hair follicle dermal condensation of skin,respectively.These marker genes were grouped in Wnt,IGF,and FGF signaling pathways,suggesting that these genes are candidates regulating morphological differences between coarse and fine wool sheep fetal skin.(4)9 differentially expressed genes were selected for qPCR validation analysis.The results showed that the expression pattern of four(FZD4,FZD9,DKK1 and BAMBI)genes were consistent with those of RNAseq.ConclusionThis study observed significant differences in skin thickness and wool follicle cross-sectional area during early embryonic development between coarse and fine wool sheep.The comparative analyses of transcriptome found that differentially expressed genes were correlated with development of the dermis and hair follicle dermal condensation,which directly or indirectly regulated the morphological differences in fetal skin between coarse and fine wool sheep.The specific function still needs to be further researched.This report is a preliminary study on the molecular networks regulating primary wool follicle development in sheep skin,and will provide new ideas to improve the quality of sheep wool fibers.