Differential transcriptomic profiling provides new insights into oocyte development and lipid droplet formation in Japanese flounder (Paralichthys olivaceus)

Abstract

The molecular mechanisms underlying the transition from primary to secondary growth stage of oocyte remain elusive in teleost. In this study, oocytes in various diameters and developmental states, including primary growth stage (PG) (~35 μm), early lipid droplet stage (EDO) (~70 μm) and late lipid droplet stage (LDO) (~100 μm) in P. olivaceus, were isolated using collagenase digestion combined with physical filtering methods in vitro. Subsequent transcriptome analysis showed that there were 2288, 3344, and 337 differentially expressed genes (DEGs) in comparison of PG-vs-EDO, PG-vs-LDO and EDO-vs-LDO, respectively. Most of the DEGs, such as members of the ZP family and the HSP family, were highly expressed at PG. Besides, some genes associated with fatty acid metabolism were up-regulated from PG to LDO. KEGG pathway analysis revealed that some DEGs were linked to Notch, Hippo, Axon guidance, and immune-related pathways including the TNF and Small cell lung cancer signaling pathway. In addition, we used the up-regulated gene set in the trend analysis to enrich for a number of signaling pathways related to the lipoprotein synthesis, including fatty acid biosynthesis, glycerolipid metabolism, glycerophospholipid metabolism, and phospholipase D signaling pathways. This study broadened our understanding of the genes and signaling pathways involved in the transition from primary to secondary oocyte growth stage, and provided some clues in regard to the mechanisms underlying lipid droplet synthesis in oocyte of teleost species.