Distribution of cionin and its receptor in the central nervous system of Ciona intestinalis type A

The cholecystokinin (CCK)/gastrin family peptides are involved in regulation of feeding and digestion in vertebrates. In the ascidian Ciona intestinalis type A (Ciona robusta), cionin, a CCK/gastrin family peptide, has been identified. Cionin is expressed exclusively in the central nervous system (CNS). In contrast, cionin receptor expression has been detected in the CNS, digestive tract, and ovary. Although cionin has been reported to be involved in ovulation, its physiological function in the CNS remains to be investigated.

To elucidate its neural function, researchers analyzed the expression of cionin and cionin receptors in the CNS. Cionin was expressed mainly in neurons residing in the anterior region of the cerebral ganglion. In contrast, the gene expression of the cionin receptor gene CioR1, was detected in the middle part of the cerebral ganglion and showed a similar expression pattern to that of VACHT, a cholinergic neuron marker gene.

Moreover, CioR1 was found to be expressed in cholinergic neurons. Consequently, these results suggest that cionin interacts with cholinergic neurons as a neurotransmitter or neuromodulator via CioR1. This study provides insights into a biological role of a CCK/gastrin family peptide in the CNS of ascidians.

This research highlights the potential for studying neural signaling pathways in non-vertebrate models using CCK-related peptides. However, further investigation is required to confirm the specific physiological roles of cionin within the central nervous system. The findings underscore the importance of understanding evolutionary conservation of peptide signaling mechanisms across species.