Transcriptome analysis based on dietary beta-carotene supplement reveals genes potentially involved in carotenoid metabolism in Crassostrea gigas

Carotenoids are essential micronutrients for animals, and they can only be obtained from the diet for mollusk as well as other animals. In the body, carotenoids undergo processes including absorption, transport, deposition, and metabolic conversion; however, knowledge of the involved genes is still limited. To elucidate the molecular mechanisms of carotenoid processing and identify the related genes in Pacific oyster (Crassostrea gigas), we performed a comparative transcriptome analysis using digestive gland tissues of oysters on a beta-carotene supplemented diet or a normal diet. A total of 718 differentially expressed genes were obtained, including 505 upregulated and 213 downregulated genes in the beta-carotene supplemented group. Function Annotation and enrichment analyses revealed enrichment in genes possibly involved in carotenoid transport and storage (e. g., LOC105342035), carotenoid cleavage (e.g., LOC105341121), retinoid homeostasis (e.g., LOC105339597) and PPAR signaling pathway (e.g., LOC105323212). Notably, down-regulation of mRNA expressions of two apoli-poprotein genes (LOC105342035 and LOC105342186) by RNA interference significantly decreased the carot-enoid level in the digestive gland, supporting their role in carotenoid transport and storage. Based on these differentially expressed genes, we propose that there may be a negative feedback mechanism regulated by nu-clear receptor transcription factors controlling carotenoid oxygenases. Our findings provide useful hints for elucidating the molecular basis of carotenoid metabolism and functions of carotenoid-related genes in the oyster.

Automated summary

Carotenoids are essential micronutrients for oysters and other animals, and the molecular mechanisms and related genes involved in carotenoid processing are still limited. In this study, a comparative transcriptome analysis of Pacific oysters was performed, revealing differentially expressed genes related to carotenoid transport, storage, cleavage, and retinoid homeostasis. Down-regulation of apoli-poprotein genes significantly decreased the carotenoid level in the oyster's digestive gland, suggesting their role in carotenoid transport and storage. These findings provide insights into the molecular basis of carotenoid metabolism and functions of carotenoid-related genes in oysters.