Lipid droplets play versatile roles in ovarian development of the razor clam Sinonovacula constricta: Insights from proteomic and lipidomic analyses.

Lipid droplet (LD) deposition is a common phenomenon during ovarian development across marine mollusks; however, studies on the protein and lipid composition of their ovarian LDs remain limited. Here, we purified LDs from the ovaries of Sinonovacula constricta and isolated proteins and lipids from these purified LDs for proteomic and lipidomic analyses. Our proteomic analysis identified 3243 proteins, with PLIN2 being the most abundant (37.03 ± 13.56 %). We subsequently conducted a functional analysis of the top 500 most abundant LD-associated proteins, categorizing them into 15 groups, including those involved in lipid metabolism, sterol biosynthesis, tricarboxylic acid cycle, carbohydrate metabolism, G protein superfamily, protein chaperones, transport proteins, nucleotide-catabolic process, protein processing and degradation, cytoskeletal proteins, oxidative stress and immunity, and ribosome-associated proteins. In our lipidomic analysis, we identified 1158 molecules across 52 lipid classes, with phosphatidylcholine (PC) exhibiting the greatest diversity at 209 varieties, followed by EtherPC with 177 varieties and triglyceride (TG) with 149 varieties. The fatty acid (FA) analysis of LDs revealed that 16:0 was the most abundant (30.01 ± 0.42 %). Additionally, LDs were found rich in long-chain polyunsaturated FAs (35.63 ± 4.36 %), particularly EPA and DHA. Moreover, we analyzed the FA composition of TGs, PCs, and EtherPCs derived from ovarian LDs. In PCs and TGs, the predominant FAs were 16:0, 16:1, and 18:3, while 16:0, 22:6, and 18:4 constituted the major FA species in EtherPCs. Together, our results suggest that ovarian LDs in S. constricta not only participate in lipid metabolism but also interact with other organelles and metabolic processes, thereby facilitating ovarian development.