The Detection Of Key Genes For Embryonic Tail Development Of Fat-tailed Sheep

As one of the largest sheep stock and mutton consumption countries,improving the performance of sheep production has always been the focal point in the field of genetics and breeding for livestock.Sheep can be divided into fat-tailed sheep,fat-rumped sheep and thin-tailed sheep according to tail types,and it is generally accepted that the fat tail is a unique trait formed by long-term natural selection and artificial breeding of thin-tailed sheep.At present,most of the researches are mainly focus on studying adult sheep with various tail type at genome and transcriptome level.However,the deposition of fat tail have begun at embryonic period.Therefore,the present study explored the key functional genes and biological pathways in the process of embryonic fat tail deposition.Based on the above background,the main researches and results are as follows.(1)The histological analysis suggested that the E70-E80 was the key time point of fat tail deposition.We collected the tail tissues of Tan sheep at 60 days(E60),70 days(E70),80days(E80)and 90 days(E90)of gestation and performed HE and Oil red staining.From E60 to E70,there didn’t have fat deposition in tail tissue and the preadipocytes gathered to regular leaf cell masses;from E70 to E80,the preadipocytes intensively proliferated and differentiated into adipocytes and lots of fat deposited in the tail tissue.(2)The time of fat deposition in the tail tissue was earlier than that in subcutaneous,intramuscular and perirenal tissues.We performed HE staining for tail,muscle,muscle,skin,liver and kidney at the same time and didn’t find fat droplets.(3)Through the hierarchical analysis for the 1066 differently expressed genes,we found six clusters finally(K1-K6)and K2 and K4 contained the largest number of DEGs.The genes enriched in K2 mainly related energy metabolism pathways,such as oxidative phosphorylation and mitochondrial component,which were upregulated in E60-E70 and down regulated.However,the genes enriched in K4 mainly related to cytolergy pathways,such as focal adhesion,ECM receptor interaction and ARVC,which express opposite expression trend compared with K2.Therefore,we thought that E60-E70 was the preparation stage for preadipocyte differentiation and fat deposition,which upregulated the genes related to energy metabolism and down regulated the genes related to cell activities to increase the oxidative phosphorylation level in cells and accumulate energy for cell proliferation,differentiation and fat deposition;E70-E80 was the stage of preadipocyte differentiation and fat deposition,during which cytolergy increased and energy accumulation activity decreased,so that,preadipocytes could proliferate and differentiate into adipocytes in a short time.(4)Mitochondria and oxidative phosphorylation happened in mitochondria played an important role in the early stage of fat tail development.Finally,we focused on 183 genes,which contains four genes(GMPR,GSTP1,SLC25A4 and EIF4EBP1)with the most significantly expressional change,and two important transcription factors,NME2 and NME4.(5)In addition,we also proved that PDGFD gene is an important regulator of fat tail phenotype by expressional studies and dual-luciferase reporter experiments.Mutations in the conserved region of the first intron are probably related to the transcriptional activity of PDGFD gene and fat deposition.The present study investigated the morphogenesis and expressional changes during fat tail development in gestation comprehensively from the perspective of histomorphology and comparative transcriptome,defined the key period of fat tail development,found the important role of mitochondria and oxidative phosphorylation,screened the key genes and transcriptional factors regulating fat tail development and provided theoretical basis for fat tail breeding.