Mechanosensory cells and swimming behaviour of embryos of the sea urchin Strongylocentrotus purpuratus.

Recent sequencing of the genome of the sea urchin Strongylocentrotus purpuratus identified Usher syndrome genes involved in photo- and mechanosensation in vertebrate retina and inner ear as well as the TRPA1 ion channel often involved in mechanosensation. Sensory cells have not been definitively identified in sea urchins despite the known photo- and mechanosensory capabilities of adults, larvae and embryos. To identify sensory cells in embryos and early larvae expression of Usher and TRPA1 genes was investigated, but did not identify candidate sensory cells. Some Usher genes were expressed in neurogenic ectoderm of embryos. Screening for cells having putative mechanosensory channels was performed using cationic fluorescent dyes and identified several types, including blastocoelar cells. Temporal expression of the TRPA1 gene and inhibition of swimming activity by ion channel inhibitors suggest its involvement in control of swimming. This study provides evidence that mechanosensory channels modulate swimming behaviour of embryos and early larvae.