PACRG is Expressed on the Left Side of the Brain Vesicle in the Ascidian Halocynthia Larva

The ascidian larvae, which display a chordate ground body plan, are left-right asymmetric in several structures, including the brain vesicle. In ascidian larvae, the ocellus and otolith pigment cells, which are thought to detect light and gravity respectively, are located on the right side of the brain vesicle, while the coronet cells, which are presumed to be dopaminergic, are located on the left side. To study how left-right asymmetry of the brain vesicle in the ascidian <i>Halocynthia roretzi</i> larva is determined, I attempted to isolate a gene that is expressed in the brain vesicle. As a result, an ascidian Parkin co-regulated gene (<i>PACRG</i>) orthologue was cloned. Expression of <i>PACRG</i> begins weakly in the head region of the late tailbud embryos, and it thereafter is observed on the left side of the brain vesicle of the larvae just before hatching. The location of <i>PACRG</i> expression is estimated to overlap with the area stained by the coronet cell-specific antibody. Thus, it is suggested that <i>PACRG</i> might be involved in the formation of the left-side structures of the brain vesicle, including coronet cells, during ascidian embryogenesis.