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1. Cataract induction in an arthropod reveals how lens crystallins contribute to the formation of biological glass

   https://doi.org/10.1371/journal.pone.0325229  

   Mitra, Amartya T; Rathore, Shubham; Jester, Augusta; Hyland-Brown, Ruby; Hassert, J; Benoit, Joshua B; Stowasser, Annette; Buschbeck, Elke K (June 2025, PLOS One)

   Yousefi, Reza (Ed.)

   Lenses are vital components of well-functioning eyes and are crafted through the precise arrangement of proteins to achieve transparency and refractive ability. In addition to optical clarity for minimal scatter and absorption, proper placement of the lens within the eye is equally important for the formation of sharp, focused images on the retina. Maintaining these states is challenging due to dynamic and substantial post-embryonic eye and lens growth. Here, we gain insights into required processes through exploring the optical and visual consequences of silencing a key lens constituent inThermonectus marmoratussunburst diving beetle larvae. Using RNAi, we knocked down Lens3, a widely expressed cuticular lens protein during a period of substantial growth of their camera-type principal eyes. We show thatlens3RNAi results in the formation of opacities reminiscent of vertebrate lens ‘cataracts’, causing the projection of blurry and degraded images. Consequences of this are exacerbated in low-light conditions, evidenced by impaired hunting behaviour in this visually guided predator. Notably, lens focal lengths remained unchanged, suggesting that power and overall structure are preserved despite the absence of this major component. Further, we did not detect significant shifts in thein-vivorefractive states of cataract-afflicted larvae. This in stark contrast with findings in vertebrates, in which form-deprivation or the attenuation of image contrast, results in the dysregulation of eye growth, causing refractive errors such as myopia. Our results provide insights into arthropod lens construction and align with previous findings which point towards visual input being inconsequential for maintaining correctly focused eyes in this group. Our findings highlight the utility ofT. marmoratusas a tractable model system to probe the aetiology of lens cataracts and refractive errors. 

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2. Drosophila Retinal Patterning

   https://doi.org/10.1038/npg.els.0001511  

   Spencer, Susan A; Johnson, Ruth I; Setu, Bipul (January 2020, Encyclopedia of life sciences)

   The Drosophila eye is an outstanding model system for exploring fundamental mechanisms of growth and development. The adult eye is composed of a perfect hexagonal lattice of ∼750 unit eyes, or ommatidia, each containing precisely 20 well-characterized cells. The eye develops from the eye/antennal imaginal disc, a flattened epithelial sac. During larval and pupal development, cells in the disc grow and undergo compartmentalisation, cell cycle arrest, differentiation, directed movement, and apoptosis, all utilising gene networks and signalling pathways similar to those in vertebrates. The genetic accessibility of Drosophila, together with the precision of eye development, makes the fly retina an extremely useful system with which to investigate the roles of genes and signalling pathways in development. 

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3. Ocular lens morphology is influenced by ecology and metamorphosis in frogs and toads

   https://doi.org/10.1098/rspb.2022.0767  

   Mitra, Amartya T.; Womack, Molly C.; Gower, David J.; Streicher, Jeffrey W.; Clark, Brett; Bell, Rayna C.; Schott, Ryan K.; Fujita, Matthew K.; Thomas, Kate N. (November 2022, Proceedings of the Royal Society B: Biological Sciences)

   The shape and relative size of an ocular lens affect the focal length of the eye, with consequences for visual acuity and sensitivity. Lenses are typically spherical in aquatic animals with camera-type eyes and axially flattened in terrestrial species to facilitate vision in optical media with different refractive indices. Frogs and toads (Amphibia: Anura) are ecologically diverse, with many species shifting from aquatic to terrestrial ecologies during metamorphosis. We quantified lens shape and relative size using 179 micro X-ray computed tomography scans of 126 biphasic anuran species and tested for correlations with life stage, environmental transitions, adult habits and adult activity patterns. Across broad phylogenetic diversity, tadpole lenses are more spherical than those of adults. Biphasic species with aquatic larvae and terrestrial adults typically undergo ontogenetic changes in lens shape, whereas species that remain aquatic as adults tend to retain more spherical lenses after metamorphosis. Further, adult lens shape is influenced by adult habit; notably, fossorial adults tend to retain spherical lenses following metamorphosis. Finally, lens size relative to eye size is smaller in aquatic and semiaquatic species than other adult ecologies. Our study demonstrates how ecology shapes visual systems, and the power of non-invasive imaging of museum specimens for studying sensory evolution. 

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4. Probing the conserved roles of cut in the development and function of optically different insect compound eyes

   https://doi.org/10.3389/fcell.2023.1104620  

   Rathore, Shubham; Meece, Michael; Charlton-Perkins, Mark; Cook, Tiffany A.; Buschbeck, Elke K. (March 2023, Frontiers in Cell and Developmental Biology)

   Astonishing functional diversity exists among arthropod eyes, yet eye development relies on deeply conserved genes. This phenomenon is best understood for early events, whereas fewer investigations have focused on the influence of later transcriptional regulators on diverse eye organizations and the contribution of critical support cells, such as Semper cells (SCs). As SCs in Drosophila melanogaster secrete the lens and function as glia, they are critical components of ommatidia. Here, we perform RNAi-based knockdowns of the transcription factor cut (CUX in vertebrates), a marker of SCs, the function of which has remained untested in these cell types. To probe for the conserved roles of cut , we investigate two optically different compound eyes: the apposition optics of D. melanogaster and the superposition optics of the diving beetle Thermonectus marmoratus . In both cases, we find that multiple aspects of ocular formation are disrupted, including lens facet organization and optics as well as photoreceptor morphogenesis. Together, our findings support the possibility of a generalized role for SCs in arthropod ommatidial form and function and introduces Cut as a central player in mediating this role. 

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5. Expression of Opsins of the Box Jellyfish Tripedalia cystophora Reveals the First Photopigment in Cnidarian Ocelli and Supports the Presence of Photoisomerases

   https://doi.org/10.3389/fnana.2022.916510  

   Garm, Anders; Svaerke, Jens-Erik; Pontieri, Daniela; Oakley, Todd H. (August 2022, Frontiers in Neuroanatomy)

   Cubomedusae, or box jellyfish, have a complex visual system comprising 24 eyes of four types. Like other cnidarians, their photoreceptor cells are ciliary in morphology, and a range of different techniques together show that at least two of the eye types—the image-forming upper and lower lens eyes—express opsin as the photopigment. The photoreceptors of these two eye types express the same opsin ( Tc LEO ), which belongs to the cnidarian-specific clade cnidops. Interestingly, molecular work has found a high number of opsin genes in box jellyfish, especially in the Caribbean species Tripedalia cystophora , most of which are of unknown function. In the current study, we raised antibodies against three out of five opsins identified from transcriptomic data from T. cystophora and used them to map the expression patterns. These expression patterns suggest one opsin as the photopigment in the slit eyes and another as a putative photoisomerase found in photoreceptors of all four eyes types. The last antibody stained nerve-like cells in the tentacles, in connection with nematocytes, and the radial nerve, in connection with the gonads. This is the first time photopigment expression has been localized to the outer segments of the photoreceptors in a cnidarian ocellus (simple eye). The potential presence of a photoisomerase could be another interesting convergence between box jellyfish and vertebrate photoreceptors, but it awaits final experimental proof. 

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