Journal
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
Volume 278, Issue 1723, Pages 3371-3379Publisher
ROYAL SOC
DOI: 10.1098/rspb.2011.0336
Keywords
sea urchin; opsins; photosensory; tube feet; echinoderm
Categories
Funding
- New Hampshire Sea Grant Programme [R/FMD-14, R/FMD-166]
- National Research Initiative, USDA [2002-35206-11631]
- northeast Regional Aquaculture Center [04-15]
- National Science Foundation [IBN-0131285]
- UNH Graduate School, Department of Zoology, Centre for Marine Biology
- Sigma Xi
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All echinoderms have unique hydraulic structures called tube feet, known for their roles in light sensitivity, respiration, chemoreception and locomotion. In the green sea urchin, the most distal portion of these tube feet contain five ossicles arranged as a light collector with its concave surface facing towards the ambient light. These ossicles are perforated and lined with pigment cells that express a PAX6 protein that is universally involved in the development of eyes and sensory organs in other bilaterians. Polymerase chain reaction (PCR)-based sequencing and real time quantitative PCR (qPCR) also demonstrate the presence and differential expression of a rhabdomeric-like opsin within these tube feet. Morphologically, nerves that could serve to transmit information to the test innervate the tube feet, and the differential expression of opsin transcripts in the tube feet is inversely, and significantly, related to the amount of light that tube feet are exposed to depending on their location on the test. The expression of these genes, the differential expression of opsin based on light exposure and the unique morphological features at the distal portion of the tube foot strongly support the hypothesis that in addition to previously identified functional roles of tube feet they are also photosensory organs that detect and respond to changes in the underwater light field.
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