Targeted knockdown of an opsin gene inhibits the swimming behaviour photoresponse of ascidian larvae.

The sequencing of the ascidian Ciona intestinalis genome was completed at the end of 2002. Effective targeted gene knockdown in this model chordate would greatly enhance understanding of how the genes affect the function of the neurons that underlie behaviour. We show here that antisense morpholinos (MOs) are effective and specific translational inhibitors in C. intestinalis larvae. The larvae developed from eggs injected with a Ci-opsin1 MO lost their photoresponse, which affected their swimming behaviour. Immunohistochemical analysis showed that the expression of Ci-opsin1, the visual pigments in the photoreceptor of the ocellus, had been lost in the larvae with the Ci-opsin1 MO. The inhibition of the photic behaviour of the knockdown larvae is solely due to the suppression of the synthesis of the visual pigments in the photoreceptors. These are the first results showing the knockdown of an ascidian gene and the elucidation of that gene's role in ascidian larval behaviour.