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The structure of compound eyes in arthropods has been the subject of many studies, revealing important biological principles. Until recently, these studies were constrained by the two-dimensional nature of available ultrastructural data. By taking advantage of the novel three-dimensional ultrastructural dataset obtained using volume electron microscopy, we present the first cellular-level reconstruction of the whole compound eye of an insect, the miniaturized parasitoid wasp Megaphragma viggianii . The compound eye of the female M. viggianii consists of 29 ommatidia and contains 478 cells. Despite the almost anucleate brain, all cells of the compound eye contain nuclei. As in larger insects, the dorsal rim area of the eye in M. viggianii contains ommatidia that are believed to be specialized in polarized light detection as reflected in their corneal and retinal morphology. We report the presence of three ‘ectopic’ photoreceptors. Our results offer new insights into the miniaturization of compound eyes and scaling of sensory organs in general.

The ocular surface of the white domestic pig (Sus scrofa domestica) is used as a helpful model of the human ocular surface; however, a complete histological description has yet to be published. In this work, we studied porcine eyeballs with intact eyelids to describe and characterize the different structures that form the ocular surface, including the cornea and conjunctiva that covers the bulbar sclera, tarsi, and the nictitating membrane. We determined the distribution of goblet cells of different types over the conjunctiva and analyzed the conjunctival-associated lymphoid tissue (CALT). Porcine eyeballs were obtained from a local slaughterhouse, fixed, processed, and embedded in paraffin blocks. Tissue sections (4 μm) were stained with hematoxylin/eosin, Alcian blue/Periodic Acid Schiff, and Giemsa. Slides were also stained with lectins from Arachis hypogaea (PNA) and Helix pomatia (HPA) agglutinins and immunostained with rabbit anti-CD3. We found that the porcine cornea was composed of 6-8 epithelial cell layers, stroma, Descemet's membrane, and an endothelial monolayer. The total corneal thickness was 1131.0±87.5 μm (mean±standard error of the mean) in the center and increased to 1496.9±138.2 μm at the limbus. The goblet cell density was 71.25±12.29 cells/mm, ranging from the highest density (113.04±37.21 cells/mm) in the lower palpebral conjunctiva to the lowest density (12.69±4.29 cells/mm) in the bulbar conjunctiva. The CALT was distributed in the form of intraepithelial lymphocytes and subepithelial diffuse lymphoid tissue. Lenticular-shaped lymphoid follicles, about 8 per histological section, were also present within the conjunctival areas. In conclusion, we demonstrated that the analyzed porcine ocular structures are similar to those of humans, confirming the potential usefulness of pig eyes to study ocular surface physiology and pathophysiology.

Melanosomes were isolated from the retinal pigment epithelium (RPE), iris and choroid of mature (age >2 years) and newborn (age <1 week) bovine eyes. Scanning electron microscopy was utilized to analyze the morphology of the melanosomes, which were found to vary among different tissues and different ages. While the total content of amino acids differs slightly (ranging from 9% to 15% by mass), the distributions of the amino acids are similar. The pheomelanin content is low in the choroid and the RPE (0.1–0.5%), and moderate in the iris (<2%); therefore, the major melanin component of bovine eye melanosomes is eumelanin, independent of the shape of the melanosomes. The yields of pyrrole-2,3,5-tricarboxylic acid from melanosomes decrease in the following order: choroid > iris > RPE, and exhibit decreasing yields with age. 13C solid-state nuclear magnetic resonance (NMR) spectroscopic analysis of iris and choroid melanosomes indicates the same trends. These observations suggest that the 5,6-dihydroxyindole-2-carboxylic acid contents decrease in the following order: choroid > iris > RPE, and decrease with age. Moreover, the 13C solid-state NMR spectra show (1) for the same age samples, the CH:Cq ratio for choroid is larger than that for iris melanosomes; and (2) an increase in the concentration of carbonyl groups with age within each type of melanosome.

With a body length of only 0.3–0.4 mm, the parasitoid wasp Trichogramma evanescens (Westwood) is one of the smallest insects known. Yet, despite its diminutive size, it possesses compound eyes that are of oval shapes, measuring across their long axes in dorsoventral direction 63.39 and 71.11 μm in males and females, respectively. The corresponding facet diameters are 5.90 μm for males and 6.39 μm for females. Owing to the small radii of curvature of the eyes in males (34.59 μm) and females (42.82 μm), individual ommatidia are short with respective lengths of 24.29 and 34.97 μm. The eyes are of the apposition kind, and each ommatidium possesses four cone cells of the eucone type and a centrally fused rhabdom, which throughout its length is formed by no more than eight retinula cells. A ninth cell occupies the place of the eighth retinula cell in the distal third of the rhabdom. The cone is shielded by two primary and six secondary pigment cells, all with no apparent extensions to the basement membrane, unlike the case in larger hymenopterans. The regular and dense packing of the rhabdoms reflects an effective use of space. Calculations on the optics of the eyes of Trichogramma suggest that the eyes need not be diffraction limited, provided they use mostly shorter wavelengths, that is, UV light. Publications on the visual behavior of these wasps confirm Trichogramma’s sensitivity to UV radiation. On the basis of our findings, some general functional conclusions for very small compound eyes are formulated.

The outer segments of vertebrate rod photoreceptors are renewed every 10 d. Outer segment components are transported from the site of synthesis in the inner segment through the connecting cilium, followed by assembly of the highly ordered discs. Two models of assembly of discrete discs involving either successive fusion events between intracellular rhodopsin-bearing vesicles or the evagination of the plasma membrane followed by fusion of adjacent evaginations have been proposed. Here we use immuno-electron microscopy and electron tomography to show that rhodopsin is transported from the inner to the outer segment via the ciliary plasma membrane, subsequently forming successive evaginations that “zipper” up proximally, but at their leading edges are free to make junctions containing the protocadherin, PCDH21, with the inner segment plasma membrane. Given the physical dimensions of the evaginations, coupled with likely instability of the membrane cortex at the distal end of the connecting cilium, we propose that the evagination occurs via a process akin to blebbing and is not driven by actin polymerization. Disassembly of these junctions is accompanied by fusion of the leading edges of successive evaginations to form discrete discs. This fusion is topologically different to that mediated by the membrane fusion proteins, SNAREs, as initial fusion is between exoplasmic leaflets, and is accompanied by gain of the tetraspanin rim protein, peripherin.

The living cell contains dynamic, spatially complex subassemblies that are sensitive to external perturbations. To minimize such perturbations, cells should be imaged in their native multicellular environments, under as gentle illumination as possible. However, achieving the spatiotemporal resolution needed to follow three-dimensional subcellular processes in detail under these conditions is challenging: Sample-induced aberrations degrade resolution and sensitivity, and high resolution usually requires intense excitation. Liu et al. combined noninvasive lattice light-sheet microscopy with aberration-correcting adaptive optics to study a variety of delicate subcellular events in vivo, including organelle remodeling during mitosis and growth cone dynamics during spinal cord development. Science , this issue p. eaaq1392 Adaptive optical lattice light-sheet microscopy permits delicate 3D subcellular processes to be viewed natively in vivo. True physiological imaging of subcellular dynamics requires studying cells within their parent organisms, where all the environmental cues that drive gene expression, and hence the phenotypes that we actually observe, are present. A complete understanding also requires volumetric imaging of the cell and its surroundings at high spatiotemporal resolution, without inducing undue stress on either. We combined lattice light-sheet microscopy with adaptive optics to achieve, across large multicellular volumes, noninvasive aberration-free imaging of subcellular processes, including endocytosis, organelle remodeling during mitosis, and the migration of axons, immune cells, and metastatic cancer cells in vivo. The technology reveals the phenotypic diversity within cells across different organisms and developmental stages and may offer insights into how cells harness their intrinsic variability to adapt to different physiological environments.

Huntington’s disease (HD) is a fatal neurodegenerative disorder caused by aberrant expansion of CAG repeat in the huntingtin gene. Mutant Huntingtin (mHtt) alters multiple cellular processes, leading to neuronal dysfunction and death. Among those alterations, impaired mitochondrial metabolism seems to have a major role in HD pathogenesis. In this study, we used the Drosophila model system to further investigate the role of mitochondrial damages in HD. We first analyzed the impact of mHtt on mitochondrial morphology, and surprisingly, we revealed the formation of abnormal ring-shaped mitochondria in photoreceptor neurons. Because such mitochondrial spheroids were previously detected in cells where mitophagy is blocked, we analyzed the effect of PTEN-induced putative kinase 1 (PINK1), which controls Parkin-mediated mitophagy. Consistently, we found that PINK1 overexpression alleviated mitochondrial spheroid formation in HD flies. More importantly, PINK1 ameliorated ATP levels, neuronal integrity and adult fly survival, demonstrating that PINK1 counteracts the neurotoxicity of mHtt. This neuroprotection was Parkin-dependent and required mitochondrial outer membrane proteins, mitofusin and the voltage-dependent anion channel. Consistent with our observations in flies, we demonstrated that the removal of defective mitochondria was impaired in HD striatal cells derived from HdhQ111 knock-in mice, and that overexpressing PINK1 in these cells partially restored mitophagy. The presence of mHtt did not affect Parkin-mediated mitochondrial ubiquitination but decreased the targeting of mitochondria to autophagosomes. Altogether, our findings suggest that mitophagy is altered in the presence of mHtt and that increasing PINK1/Parkin mitochondrial quality control pathway may improve mitochondrial integrity and neuroprotection in HD.

Background An emerging cavefish model, the cyprinid genus Sinocyclocheilus , is endemic to the massive southwestern karst area adjacent to the Qinghai-Tibetan Plateau of China. In order to understand whether orogeny influenced the evolution of these species, and how genomes change under isolation, especially in subterranean habitats, we performed whole-genome sequencing and comparative analyses of three species in this genus, S. grahami , S. rhinocerous and S. anshuiensis . These species are surface-dwelling, semi-cave-dwelling and cave-restricted, respectively. Results The assembled genome sizes of S. grahami , S. rhinocerous and S. anshuiensis are 1.75 Gb, 1.73 Gb and 1.68 Gb, respectively. Divergence time and population history analyses of these species reveal that their speciation and population dynamics are correlated with the different stages of uplifting of the Qinghai-Tibetan Plateau. We carried out comparative analyses of these genomes and found that many genetic changes, such as gene loss (e.g. opsin genes), pseudogenes (e.g. crystallin genes), mutations (e.g. melanogenesis-related genes), deletions (e.g. scale-related genes) and down-regulation (e.g. circadian rhythm pathway genes), are possibly associated with the regressive features (such as eye degeneration, albinism, rudimentary scales and lack of circadian rhythms), and that some gene expansion (e.g. taste-related transcription factor gene) may point to the constructive features (such as enhanced taste buds) which evolved in these cave fishes. Conclusion As the first report on cavefish genomes among distinct species in Sinocyclocheilus , our work provides not only insights into genetic mechanisms of cave adaptation, but also represents a fundamental resource for a better understanding of cavefish biology.

The eyes of the Tully monster ( Tullimonstrum ) possess ultrastructural details indicating homology with vertebrate eyes. Illinois' Tully monster reinterpreted Since its discovery in 1958 by Francis Tully in the approximately 300-million-year-old Mazon Creek fossil beds in Illinois, the zoological affinities of the soft-bodied animal popularly known as the Tully monster ( Tullimonstrum gregarium ) have remained mysterious. It is a remarkable looking creature, with a fish-like body featuring prominent eyes at each end of a horizontal bar, and jaws on the end of a long, jointed proboscis. Its origins have been compared variously with nemertean and polychaete worms, molluscs, conodonts and even stem-group arthropods. Now two papers in this issue identify Tullimonstrum securely as a vertebrate. Thomas Clements et al . studied the eyes and found ultrastructural details indicating homology with those of vertebrates. Victoria McCoy et al . examined more than 1,200 specimens. They re-interpret many known features, and describe and interpret many new ones: all are consistent with Tullimonstrum being a vertebrate, akin to lampreys and increasing the morphological disparity of that group. Tullimonstrum gregarium is an iconic soft-bodied fossil from the Carboniferous Mazon Creek Lagerstätte (Illinois, USA) 1 . Despite a large number of specimens and distinct anatomy, various analyses over the past five decades have failed to determine the phylogenetic affinities of the ‘Tully monster’, and although it has been allied to such disparate phyla as the Mollusca 2 , Annelida 3 , 4 or Chordata 5 , it remains enigmatic 1 , 2 , 3 , 4 , 5 . The nature and phylogenetic affinities of Tullimonstrum have defied confident systematic placement because none of its preserved anatomy provides unequivocal evidence of homology, without which comparative analysis fails. Here we show that the eyes of Tullimonstrum possess ultrastructural details indicating homology with vertebrate eyes. Anatomical analysis using scanning electron microscopy reveals that the eyes of Tullimonstrum preserve a retina defined by a thick sheet comprising distinct layers of spheroidal and cylindrical melanosomes. Time-of-flight secondary ion mass spectrometry and multivariate statistics provide further evidence that these microbodies are melanosomes. A range of animals have melanin in their eyes, but the possession of melanosomes of two distinct morphologies arranged in layers, forming retinal pigment epithelium, is a synapomorphy of vertebrates. Our analysis indicates that in addition to evidence of colour patterning 6 , ecology 7 and thermoregulation 8 , fossil melanosomes can also carry a phylogenetic signal. Identification in Tullimonstrum of spheroidal and cylindrical melanosomes forming the remains of retinal pigment epithelium indicates that it is a vertebrate; considering its body parts in this new light suggests it was an anatomically unusual member of total group Vertebrata.

Oxidative damage and inflammation are postulated to be involved in age-related macular degeneration (AMD). However, the molecular signal(s) linking oxidation to inflammation in this late-onset disease is unknown. Here we describe AMD-like lesions in mice after immunization with mouse serum albumin adducted with carboxyethylpyrrole, a unique oxidation fragment of docosahexaenoic acid that has previously been found adducting proteins in drusen from AMD donor eye tissues 1 and in plasma samples 2 from individuals with AMD. Immunized mice develop antibodies to this hapten, fix complement component-3 in Bruch's membrane, accumulate drusen below the retinal pigment epithelium during aging, and develop lesions in the retinal pigment epithelium mimicking geographic atrophy, the blinding end-stage condition characteristic of the dry form of AMD. We hypothesize that these mice are sensitized to the generation of carboxyethylpyrrole adducts in the outer retina, where docosahexaenoic acid is abundant and conditions for oxidative damage are permissive. This new model provides a platform for dissecting the molecular pathology of oxidative damage in the outer retina and the immune response contributing to AMD.