Abstract
Cephalopods are famous for their ability to change color and pattern rapidly for signaling and camouflage. They have keen eyes and remarkable vision, made possible by photoreceptors in their retinas. External to the eyes, photoreceptors also exist in parolfactory vesicles and some light organs, where they function using a rhodopsin protein that is identical to that expressed in the retina. Furthermore, dermal chromatophore organs contain rhodopsin and other components of phototransduction (including retinochrome, a photoisomerase first found in the retina), suggesting that they are photoreceptive. In this study, we used a modified whole-mount immunohistochemical technique to explore rhodopsin and retinochrome expression in a number of tissues and organs in the longfin squid, Doryteuthis pealeii. We found that fin central muscles, hair cells (epithelial primary sensory neurons), arm axial ganglia, and sucker peduncle nerves all express rhodopsin and retinochrome proteins. Our findings indicate that these animals possess an unexpected diversity of extraocular photoreceptors and suggest that extraocular photoreception using visual opsins and visual phototransduction machinery is far more widespread throughout cephalopod tissues than previously recognized.
Highlights
Cephalopods are well known for their remarkable ability to transform their appearance by altering their dermal coloration, patterning, and shape
Blue labeling seen in the outer segments represents autofluorescence of that
These results serve as a positive control for the protocol and provide confirmation that antibodies label the proteins of interest, as expression of rhodopsin and retinochrome in cephalopod retinas are well known [7,16], and that these antibodies label with the same pattern as thinly cryo-sectioned D. pealeii retinas [7,8]. α-tubulin labeling of axons at the proximal portion of the retina serves as a positive control, confirming that the antibody labels nerves
Summary
Cephalopods are well known for their remarkable ability to transform their appearance by altering their dermal coloration, patterning, and shape. They are thought to achieve this by detecting visual scenes using their eyes and controlling their dynamic patterning in a top-down manner. It has been shown that several cephalopod species have extraocular photoreceptors in parolfactory vesicles and epistellar bodies, both in the central nervous system[5]. These are functional partly because of the translucent skin of cephalopods.
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