Molecular characterization and functional analysis of adrenergic like receptor during larval metamorphosis in Crassostrea angulata

Numerous reports have associated the catecholamines with larval settlement and metamorphosis in bivalve mollusks. However, little information about the receptors during larval development is available. In this study, for the first time we clone and characterize the cDNAs designated as adrenergic-like receptor (ARcga) from Crassostrea angulata. The deduced protein ARcga has high similarity with α2-adrenergic receptor (α2-AR) from Ixodes scapularis, and includes three major domains composed of a transmembrane domain with seven transmembrane motifs, a relatively long third cytoplasmic loop and a short fourth inner terminal domain. Using a real-time PCR approach, expression profiles of the ARcga were analyzed in adult tissues and during larval development. In adult oyster, the ARcga was expressed ubiquitously, although transcript levels varied between organs; the highest mRNA level was detected in labium followed by mantle and gonad. ARcga expression increased during larval development and reached the highest level at eyespot larvae, and then the expressions were maintained in a high level during metamorphosis. The temporal and spatial expression profile of mRNA was examined from trochophore to eyespot larva stages by whole mount in situ hybridization. In the four stages, ARcga mRNA was mainly detected in the cerebral ganglion and or the apical organ, the pedal ganglion and around the heart. The ganglion differentiation was found in the early umbo-veliger larva. To evaluate the possible regulation of ARcga by adrenaline in the oyster metamorphosis, competent larvae were exposed to the neurotransmitter adrenaline. ARcga expression increased for the first 12 h after treatment and then ARcga mRNA level decreases gradually to the same level of untreated control group. Overall, these results suggest that ARcga might play a considerable role in signal transduction during the larval metamorphosis of C. angulata

► ARcga cDNA was characterized from the oyster Crassostrea angulata.
► ARcga mRNA expression varied between organs.
► ARcga mRNA were expressed increasingly from trocophora to eyespot larvae.
► ARcga mRNA was regulated by the metamorphosis inducer adrenaline.
► ARcga mRNA was mainly distributed in the apical organ and or cerebral ganglion.