title: Sea urchin tube feet are photosensory organs that express a rhabdomeric-like opsin and PAX6.
abstract: 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.
authors: Department of Molecular, Cellular and Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA. mpl@unh.edu
authors: Michael P
authors: MP
authors: Lesser
authors: Karen L
authors: KL
authors: Carleton
authors: Stefanie A
authors: SA
authors: Böttger
authors: Thomas M
authors: TM
authors: Barry
authors: Charles W
authors: CW
authors: Walker
mesh_terms: D000595:Amino Acid Sequence; D000825:Animal Structures / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D005121:Extremities / Q000502:physiology*; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry; D055537:Light Signal Transduction / Q000502:physiology*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D055355:Opsins / Q000235:genetics / Q000378:metabolism*; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D060888:Real-Time Polymerase Chain Reaction; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012617:Sea Urchins / Q000378:metabolism / Q000502:physiology*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D017931:DNA Primers; D005136:Eye Proteins; D018398:Homeodomain Proteins; D055355:Opsins; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D012097:Repressor Proteins