Effect of Kisspeptin-Type Neuropeptide on Locomotor Behavior and Muscle Physiology in the Sea Cucumber Apostichopus japonicus

SIMPLE SUMMARY: The sea cucumber Apostichopus japonicus is an important aquatic invertebrate, which has high nutritional and medicinal value. Kisspeptins are neuropeptides encoded by the kiss1 gene, and little is known about them outside of the vertebrate lineage. In this study, we investigated the effect of KPs on locomotor behavior in one control group and two treatment groups (AjK1 and AjK2). We found that AjK1 had a significant dose effect, mainly by reducing the stride length and duration of movement to decrease the movement distance of sea cucumbers, whereas AjK2 had little inhibitory effect at the same dose. The levels of phosphatidylethanolamine (PE), phosphatidylcholine (PC),uridine, glycine, and L-serine in the longitudinal muscle of A. japonicus treated with AjK1 differed significantly from those of the control, which may explain the observed changes in locomotor behavior. ABSTRACT: Kisspeptins are neuropeptides encoded by the kiss1 gene, and little is known about them outside the vertebrate lineage. Two kisspeptin-type neuropeptides (KPs) have been discovered in Apostichopus japonicus (AjK1 and AjK2), an edible sea cucumber, and have been linked to reproductive and metabolic regulation. In this study, we evaluated how KPs affected locomotor behavior in one control group and two treatment groups (AjK1 and AjK2). We discovered that AjK1 had a significant dose effect, primarily by shortening the stride length and duration of movement to reduce the sea cucumber movement distance, whereas AjK2 had little inhibitory effect at the same dose. The levels of phosphatidylethanolamine (PE), phosphatidylcholine (PC), uridine, glycine, and L-serine in the longitudinal muscle of A. japonicus treated with AjK1 differed significantly from those of the control, which may explain the observed changes in locomotor behavior. Treatment with AjK2 induced changes in aspartate levels. Our results imply that AjK1 is more likely than AjK2 to have a role in the regulation of A. japonicus locomotion.