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Fossilized eyes permit inferences of the visual capacity of extinct arthropods.sup.1-3. However, structural and/or chemical modifications as a result of taphonomic and diagenetic processes can alter the original features, thereby necessitating comparisons with modern species. Here we report the detailed molecular composition and microanatomy of the eyes of 54-million-year-old crane-flies, which together provide a proxy for the interpretation of optical systems in some other ancient arthropods. These well-preserved visual organs comprise calcified corneal lenses that are separated by intervening spaces containing eumelanin pigment. We also show that eumelanin is present in the facet walls of living crane-flies, in which it forms the outermost ommatidial pigment shield in compound eyes incorporating a chitinous cornea. To our knowledge, this is the first record of melanic screening pigments in arthropods, and reveals a fossilization mode in insect eyes that involves a decay-resistant biochrome coupled with early diagenetic mineralization of the ommatidial lenses. The demonstrable secondary calcification of lens cuticle that was initially chitinous has implications for the proposed calcitic corneas of trilobites, which we posit are artefacts of preservation rather than a product of in vivo biomineralization.sup.4-7. Although trilobite eyes might have been partly mineralized for mechanical strength, a (more likely) organic composition would have enhanced function via gradient-index optics and increased control of lens shape. Comparing the eyes of crane-fly fossils with those of extant species demonstrates that they contain eumelanic screening pigments and that the lenses are calcified during fossilization, with implications for interpreting optical systems in other extinct arthropods such as trilobites., Author(s): Johan Lindgren [sup.1] , Dan-Eric Nilsson [sup.2] , Peter Sjövall [sup.3] , Martin Jarenmark [sup.1] , Shosuke Ito [sup.4] , Kazumasa Wakamatsu [sup.4] , Benjamin P. Kear [sup.5] , [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.01.007 Byline: J.R. Turner (a), E.M. White (a), M.A. Collins (b), J.C. Partridge (a), R.H. Douglas (c) Keywords: Visual pigments; Bioluminescence; Lanternfish; Myctophidae; Spectral sensitivity; Visualisation distance Abstract: The sensitivity hypothesis seeks to explain the correlation between the wavelength of visual pigment absorption maxima (I'.sub.max) and habitat type in fish and other marine animals in terms of the maximisation of photoreceptor photon catch. In recent years its legitimacy has been called into question as studies have either not tested data against the output of a predictive model or are confounded by the wide phylogeny of species used. We have addressed these issues by focussing on the distribution of I'.sub.max values in one family of marine teleosts, the lanternfish (Myctophidae). Visual pigment extract spectrophotometry has shown that 54 myctophid species have a single pigment in their retinae with a I'.sub.max falling within the range 480-492nm. A further 4 species contain two visual pigments in their retinae. The spectral distribution of these visual pigments seems relatively confined when compared to other mesopelagic fishes. Mathematical modelling based on the assumptions of the sensitivity hypothesis shows that, contrary to the belief that deep-sea fishes' visual pigments are shortwave shifted to maximise their sensitivity to downwelling sunlight, the visual pigments of myctophids instead seem better placed for the visualisation of bioluminescence. The predicted maximum visualisation distance of a blue/green bioluminescent point source by a myctophid was up to 30m under ideal conditions. Two species (Myctophum nitidulum and Bolinichthys longipes) have previously been shown to have longwave-shifted spectral sensitivities and we show that they could theoretically detect stomiid far-red bioluminescence from as far as ca. 7m. Author Affiliation: (a) School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK (b) British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 OET, UK (c) Department of Optometry and Visual Science, City University, Northampton Square, London EC1V 0HB, UK Article History: Received 10 June 2008; Revised 5 January 2009; Accepted 15 January 2009

Nuclear magnetic resonance analysis reveal that 11-cis-locked cyclopropyl retinal adopts a twist chair conformation, involving the seven-membered ring, in solution. Data indicate that the compound exists as two diastereomeric populations. The native retinal does not exhibit twist preference around C6/C7 bond.

Comparison of the molecular properties of the visual pigments chicken blue, chicken green, chicken red and rhodopsin found that the faster decay of enzymatically active state is common in cone visual pigments and is independent of their spectral sensitivity. Data indicate that retinal chromophore changes its position relative to the amino acid residues during the lumi-to-meta I transition. These residues are those that regulate the maxima of original pigments through electrostatic interactions. Other residues regulate the thermal reactions of the visual pigments.

A visual pigment-like protein, referred to as peropsin, has been identified by large-scale sequencing of cDNAs derived from human ocular tissues. The corresponding mRNA was found only in the eye, where it is localized to the retinal pigment epithelium (RPE). Peropsin immunoreactivity, visualized by light and electron microscopy, localizes the protein to the apical face of the RPE, and most prominently to the microvilli that surround the photoreceptor outer segments. These observations suggest that peropsin may play a role in RPE physiology either by detecting light directly or by monitoring the concentration of retinoids or other photoreceptor-derived compounds.

Raman microprobe spectroscopy was used to investigate the wavelength mechanism in human green and red cone pigments. Results have shown that the opsin shift from rhodopsin to green pigment was determined by the weakening of the interaction of the rhodopsin chromophore with a protein hydrogen bond donor which lies adjacent to the protonated Schiff base group. Interactions between the hydroxyl group with amino acids and chromophore caused a red shift in the red cone pigment.

Low temperature spectroscopy enables an analysis of the photobleaching processes in gecko blue and gecko green, two visual pigments form the retina of Tokay gecko, which are purified by column chromatography. The photobleaching phenomenon in gecko green constitutes six intermediates, of which three are meta I, meta II and meta III. These three intermediates are present in the photobleaching process of gecko blue also. The meta II intermediate of both the pigments is thermally less stable than metarhodopsin II. The results indicate a cone-type structure for both the gecko visual pigments.

Studies of the molecular properties of chicken green and comparison with rhodopsin reveal that chicken green molecular extinction coefficient and photosensitivity are the same as that of rhodopsin. Chicken green is faster than rhodopsin in terms of regeneration from opsin moieties and the chromophore 11-cis-retinal and formation of the physiologically-active intermediate. These differences are similar to the physiological differences that exist between cones and rods.

Some combinations of sequences of the red and green pigment genes of X-chromosomal-linked gene arrangement provide individuals with selective ability by interacting at the neuronal level of color perception. The coevolution of tandemly repeated genes involves sequence homogenization and natural selection. Natural selection prevents the gene conversion at residues and promotes spectral tuning of photopigments.

The hydrogen-substituted analogue of 11-cis-retinal, 11-cis-9-desmethylretinal, adds to opsin in the bleached rods to generate defective photoproducts and enhance the quantal response amplitude of the visual pigment rhodopsin. Light activation reduces the quantal response and the decay rate of the pigment. This indicates that 9-methyl group is not essential for opsin transformation to the nondesensitizing state.

Visual pigment bacteriorhodopsin (bR) does not depend on the covalent bond between the protein backbone and retinal chromophore for its basic structure, proton pump activity and photochemical features. The mutant protein k216G with retinal alkylamine Schiff bases is used to prepare bR pigments that lack retinal-Lys-216 covalent bond.

The wildtype bovine opsin gene and several cysteine mutants were expressed in COS cellsand the expressed protein was analyzed for palmitoylation patterns. The resultsshowed that palmitoylation was specific for Cys-322 and Cys-323. The analyses also identified specific residues critical for folding and compartmentalization. Nonpalmitoylation of Cys-323 and Cys-322 did not affect the interaction with transducin or rhodopsin kinase, indicating that palmitoylation is not essential for the functional efficiency of C-terminus.

The photoreceptor cells of the nocturnal geckos consists of only the rod type. These photoreceptor cells contain the visual pigments P521 and P467. The cDNAs coding for these photopigments were isolated and characterized. Sequence analysis showed that P521 is highly similar to iodopsin, while P467 is similar to the chicken green-sensitive cone visual pigment. These results indicate that the visual pigments are more resistant to evolutionary changes than the morphology of the photoreceptors. The rod-shaped photoreceptors most likely arose from cones, as evidenced by the presence of cone-associated pigments in the rod cells of geckos.

A new type of visual pigment fromchicken was analyzed and its amino acid sequence determined. The amino acid sequence was found to approximate bovine, human and chicken rhodopsin. Photobleaching difference spectrum analysis showed that the pigment absorbs maximally at 495 nm and hydroxylamine reactivity at 20 degrees Celsius with 50nm hydroxylamine concentration at 16-minute half time.

Using a single-beam, wavelength-scanning, dichroic microspectrophotometer, we measured absolute absorbance, bleaching difference absorbance, and linear dichroism spectra from isolated retinal receptors of the black sea bass, Centropristis striata. We determined, among other properties, the wavelength of peak [alpha]-band absorbance ([lambda.sub.max]) of the pigment of the receptor cells. Out of well over 100 recordings, we found only 3 spectral types of visual pigment. The shortest-wavelength-absorbing type ([lambda.sub.max] = 463 [plus or minus] 2 nm) was present only in single cones. Both members of the double cones contained the longest-wavelength-absorbing pigment of the three, with [lambda.sub.max] = 527 [plus or minus] nm. Rods were found to bear a typical rhodopsin, with [lambda.sub.max] = 498 [plus or minus] 2 nm. Thus, the retina of this predatory demersal fish appears to use a set of three closely spaced visual pigments, with [lambda.sub.max] clustering about 500 [plus or minus] 30 nm. this remarkable feature is discussed in relation to photic conditions in the habitat.

A projection map of rhodopsin showing the configuration of its helices is presented. Rhodopsin is a visual pigment containing 348 amino acids, and has been characterized as having seveen helices crossing the disk membrane and an extracellular amino-terminus. Reconstitution of bovine rhodopsin into lipid bilayers yieelded 2-dimensional crystals, which were then analyzed by optical diffraction methods. The projection map provides a framework by which the abundant biochemical data for the protein can be interpreted.