Gonadal Lipid Storage in Mytilus coruscus: A Comprehensive Gene Network and Key Gene Discovery

The hard-shelled mussel (Mytilus coruscus), a commercially vital bivalve in China, accumulates lipids predominantly in its gonads, the species' primary edible tissue. Understanding the molecular mechanisms underlying gonad-specific lipid storage is critical for improving reproductive efficiency and aquaculture yield. This study employs comparative transcriptomic analysis of multiple tissues (gonad, gill, mantle, foot, hemolymph) to pinpoint key regulatory genes involved in lipid deposition. Through weighted gene co-expression network analysis (WGCNA), vitellogenin (VG), perilipin (PLIN), and transmembrane protein (TM) were identified as hub genes in gonadal lipid regulation. Genomic characterization revealed 13 VG and three PLIN family members in M. coruscus, which displayed conserved structural motifs and were syntenic with related bivalves, underscoring their functional significance. Phylogenetic analyses further highlighted the evolutionary conservation of these lipid-associated genes across marine invertebrates. Concurrently, sex-specific metabolic divergence was investigated. Physiological validation demonstrated that ovarian crude fat content exceeded testicular levels by 36%, corroborated histologically by larger, more stable lipid droplets in female gonads. Sex-specific expression profiling uncovered pronounced divergence: VG and PLIN were markedly enriched in ovaries, whereas glucose-6-phosphatase (G6P), a driver of energy catabolism, was elevated in testes. This study provides a molecular framework for understanding reproductive lipid metabolism in bivalves, offering biomarkers to refine broodstock management and aquaculture practices.