Comparative Proteomics Exploring The Biological Mechanism Of Large Adipose Accumulated In Tail Or Rump Of Fat-tailed Sheep

Fat-tail as a stable inheritance of phenotype which plays an important role as a survival mechanism for the fat-tailed sheep, but the fat of livestock has lost much of its market demand with the requiement of people’s healthy diet, so it’s valuable to let tail fat as little as possible by the selection. Few studies on the molecular mechanism and morphogenesis of the development of adipose tissue both in fat-tailed and thin-tailed sheep especially no major genes related to this phenotype were found, the early growth priod is very important time for the lamb to accumulated fat in tail, but no studies focus on this priod, there must be an incomprehensible reason for the genetic mechanism of fat deposition in the tail or rump of fat-tailed sheep. In this study, we observe the morphology of different fatty tissue from 5 sheep breeds by cryo-sectioning technique, along with the determination of fatty acid composition of three main adipose tissue in lamb by GC-MS(gas chromatography-mass spectrometer), after the protein extraction from the lambs’ tail adipose tissues in 5 breeds and trypsin digestion in liquid as well as phosphopeptides were enriched by IMAC, then followed by LC-MS(liquid chromatography-mass spectromitry) identification and bioinformatics analysis, finally, function analysis of the key protein by western blot, immunohistochemistry and immunofluorescence, revealing the biological mechanisms involved in the formation and development of those different tail adipose tissues.1. The adipocyte size of all the fatty tissues in fat-tailed lamb were significantly bigger than that in thin-tailed during early growth period, including the tail adipose tissue, also the cell size of adipocytes became lager with age. Compared with thin-tailed that the tail adipose tissue of fat-tailed developed early and with a higher efficiency of fat accumulation, with adipocyte cell number initially increasing, followed by an increasing in cell size when keep on a high-fat diet. The tail adipose tissue with a rapid development at early growth period that is very important for the tail fat accumulation of the fat-tailed sheep.2. The fatty acids profile of different adipose tissues were dominated by C18 Cis-9:1, C16:0 and C18:0, which comprised more than 80% total fatty acids in all the 5 breeds, PCA analysis of the fatty acid composition showed that there were a great deal of discrepancies between fat-tailed and thin-tailed lamb, presumably due to tissue specificity and breed differences.3. 3400 proteins were identified in the five groups, among them, 804 differentially expressed proteins were found. Some of high expression proteins related to the function of lipogenesis and fatty acid biosynthesis were deteced in fat-tailed lamb, which were beneficial to the development of the tail adipose tissue, a few proteins involved in the degradation of fatty acids were also high in fat-tailed lamb, which indicates the cell differentiation is necessary to increase cell number at lamb just for preparing the fat accumulation subsequently, therefore metabolic progess is requrement to creat enough capacity. Realtime PCR and Western blot tecniques were used to detect the expression of some protein and the results were almost consistent with the data of proteomics. FABP4 and ERK2 with high expression in the capillary wall were found in the tail adipose tissue of the fat-tailed lamb which may be benefit to the cell proliferation and fatty acids transportation from the blood to the fat cells. The FABP4 gene expression in fat-tail can be considered as an important index of fat deposition. ACSL1 is important for adipocyte differentiation culminating in triacylglycerol(TAG) synthesis and storage which was found high expression in fat-tailed lamb.4. We identified 1493 high-confidence phosphosites on 804 proteins which were mainly involved in translation, gene expression, protein metabolism, cell morphology, cytoskeleton, protein degradation, cell apoptosis and protein modification, it indicates that the development of adipose tissue requires these biological functions, 435 differentially phosphorylated proteins were detected in our study and among them 28 proteins involved in protein phosphorylation which may be important for the tail adipocyte development, the differentially phosphorylated proteins were related to cytoskeleton, the positive regulation of protein translation, apoptotic signal pathway regulation and so on, finally the result also contained the minimal ERK1/2 consensus motif, indicating ERK1/2 may take part in the positive regulation of adipogenesis.This study focus on the biological mechanism of the large fat deposition in tail of fat-tailed sheep, with the effect of intervention on the expression of proteins related to adipocyte differentiation and fat deposition may prevent the normal development of the tail adipose tissue at the ealy growth priod of the fat-tail lamb, which is of great significance in breeding practice to let fat tail to be thin.