Evolutionary conservation of the cholecystokinin/gastrin signaling system in nematodes.

Members of the cholecystokinin (CCK)/gastrin family of peptides, including the arthropod sulfakinins and their cognate receptors, play an important role in the regulation of feeding behavior and energy homeostasis. By using the potential Caenorhabditis elegans CCK receptors as bait, we have isolated and identified two CCK-like neuropeptides as the endogenous ligands of these nematode receptors. Both receptors and ligands share a high degree of sequence similarity with their vertebrate and arthropod counterparts and also display similar biological activities with respect to digestive enzyme secretion and fat storage. Our data indicate that the CCK/gastrin signaling system was already well established prior to the divergence of protostomes and deuterostomes.