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Transcriptome analysis provides insights into a molecular mechanism of histamine response in the cyprid larvae of Amphibalanus amphitrite

: Barnacles are notorious marine fouling creatures; their planktonic cyprid larvae attach to material substrates and metamorphose. Histamine has shown great importance in regulating cyprid settlement and metamorphosis. This study aimed to investigate the mechanisms of histamine-induced larval settlement. Cyprids were exposed to histamine or loratadine, an anti-histamine compound. The percent larval settlements of the histamine-and anti-histamine-treated cyprids were significantly higher and lower, respectively, than the control group. Transcriptomic analyses showed that histamine-treated cyprids had 18 498 differentially expressed genes (DEGs, 14 531 up-regulated, 3967 down-regulated) and the anti-histamine group had 18 055 DEGs (17 237 up-regulated, 818 down-regulated) in comparison to untreated controls. In both treatment groups, significant enrichment of DEGs involved in the mitogen-activated protein kinase signaling pathway was observed. Based on the results of larval settlement bioassays, we set 4 filter conditions to perform DEG analyses, and 19 DEGs were selected as functional genes related to cyprid settlement. The functional categories of these genes included structural proteins, spider silk proteins, energy metabolism proteins, cement proteins, glycosyl proteins, and multifunctional proteins. The energy metabolism protein AdipoR was significantly up-regulated in the histamine-treated cyprids but significantly down-regulated in the anti-histamine group. The activity of adenosine monophosphate-activated protein kinase, a downstream signaling protein of AdipoR, increased in the histamine-treated group and decreased in the anti-histamine-treated group. Our results provide new insights into the molecular mechanisms underlying the histamine-induced settlement of barnacle cyprids and identify AdipoR as an im portant gene that can affect the settlement of cyprids, likely through regulating cyprid energy metabolism.