Opsin4, Opsin5, and Pax6 significantly increase their expression in recently settled juveniles of the sea urchin Strongylocentrotus intermedius (Echinodermata: Echinoidea)

Detection of light is essential for the interaction of sea urchins with a complex marine environment because it strongly affects various behavioral and physiological responses. Gene expression patterns of related genes of photoreceptor cells during larva development and metamorphosis in sea urchins remain unknown. We investigated the expression patterns of two representative opsin genes (Opsin4 and Opsin5) and Pax6 during larva development and after metamorphosis in the sea urchin Strongylocentrotus intermedius. Gene expression patterns of SIPax6, SIOpsin4, and SIOpsin5 were significantly different during the experimental period (p < 0.001). Expression of SIPax6 generally increased from the blastula stage to the eight-arm larva. However, SIOpsin5 and SIOpsin4 kept a relatively low expression during the whole experimental period except for a significant increase at the stage of early post-metamorphosis (23days after fertilization) (p < 0.001). Like the expression pattern of SIOpsin4 and SIOpsin5, SIPax6 significantly increased its expression from the eight-arm larva stage to the juvenile (p < 0.001). After the high expression in early settled juveniles, however, the expression of all the three genes significantly decreased to a level similar to that in eight-arm larvae (p < 0.05).