Histological and transcriptomic analysis of the white hepatopancreas in Amphioctopus fangsiao

Ink production and release is one of the most important defense strategies in cephalopods. Previous studies have shown that ink production and release are closely associated with the hepatopancreas. In octopuses, the ink sac is embedded within the hepatopancreas, and the surrounding hepatopancreatic tissue appears white. To explore the differences between the white hepatopancreas and normal hepatopancreas, as well as the potential function of the white hepatopancreas, this study took Amphioctopus fangsiao as the research object and conducted histological and transcriptomic studies on white hepatopancreas and normal hepatopancreas tissues. Histological analysis revealed clear structural differences between the two tissues, with lipid droplets absent in the white hepatopancreas. Transcriptomic analysis identified 6530 differentially expressed genes (DEGs). Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and protein-protein interaction (PPI) analyses found that oxidative phosphorylation and the Apelin signaling pathways were significantly enriched in white hepatopancreas, suggesting an increase in ATP production and the alleviation of oxidative stress. Members of the ABHD gene family enriched may regulate lipid droplet metabolism. TAT, SLC6A6, Dop1R1 and Dop2R could potentially influence the levels of tyrosine, taurine and dopamine in the white hepatopancreas. Considering that these substances are involved in the main components of ink, we speculate that these genes may be related to the precursor supply for ink production. Our study demonstrates that the white hepatopancreas is structurally distinct from the normal hepatopancreas, and may be functionally related to the ink sac to some extent.