Weighted Gene Coexpression Network Analysis (WGCNA) Identify The Fat Deposition Gene In Pig Oocytes

As an organelles for energy storage in cells, lipid droplets regulates the storage and utilization of fatty acids and maintain energy balance. Moreover, it has the function of signal transduction and immunity. In the process of oocyte maturation, fertilization and early embryo development, lipid droplets are the source of endogenous lipids in oocytes, which provide energy for oocytes. However, the abnormal deposition of lipids in oocytes increases the sensitivity of oocytes to cryopreservation.Compared to other mammalian oocytes, porcine oocytes contain more abundant lipid droplets. Mainly based on this physiological characteristics, this study use microarray data analysis of porcine oocyte transcriptome, explored the lipid deposition molecular mechanism. The main results of this study in the following sections:1. Used Sudan III staining and oil red O staining of pig oocyte, and HE staining of porcine adipose tissue, We further validated the physiological characteristics of the lipid droplet content in porcine oocytes.2. In order to explore the molecular mechanism of lipid deposition in porcine oocytes, we used eight tissues of pig (COCs, fat, muscle, liver, lung, kidney, blood and testis) for the unsupervised hierarchical clustering analysis. Through hierarchical clustering analysis, we find that oocyte cumulus cells and adipose tissue belong to the same branch and separate with other organizations. Reproductive related testis and oocyte clustering distance is farther. It showed that the expression pattern of porcine oocytes and adipose tissue was more similar than other tissues. There may be have similar model between oocyte and fat in lipid deposition.3. To further explore the similarities of the oocyte and adipose tissue, we use WGCNA in eight tissues of pig, to explore different tissue specific expression module and lipid droplets related modules. Finally, the tissue specific modules were found in the oocytes, fat, testis, lung, blood and muscle. The correlation coefficient of the specific modules of those tissue is more than 0.8, and the correlation coefficient of the individual modules is more than 0.95. This indicates the relative specific expression of tissue specific modules. Through the function enrichment analysis, we found that different tissue related modules were closely related to the biological function of the tissue. It is proved that the method has high reliability.4. We finally found a module with 34 genes (r=0.9), which is highly related to the deposition of lipid droplets. The functional enrichment analysis of the module found that this module mainly in the process of fat metabolism and lipid metabolism, and related to the formation of lipid droplets. In these 34 genes,5 genes were specific expressed in oocytes and adipose tissue. 5. In order to reduce the screening range, we further analyze the lipid droplet related modules. we found 10 hub genes. In these 10 hub genes,4 genes were found to be highly expressed in oocytes and adipose tissue, and 8 genes were reported to be related to fat metabolism, lipid droplet formation and obesity, which contains fatty acid synthase (FASN), cathepsin K (ctsk), interleukin 6 (IL-6), perilipinl(plinl), ATP citrate lyase ACLY etc. They all known as fat metabolism closely related genes. TMEM229A and PATL1, are not related to lipid droplet formation at present. They can be used at the next step in the study of genes associated with lipid droplet deposition.These results suggest that porcine oocyte and adipose tissue have co-expression patterns in the deposition. We finally found a module that is associated with lipid droplet deposition, which provides the target gene for the further study of oocyte lipid deposition.