The origin of vertebrate eyes is still enigmatic. The "frontal eye" of amphioxus, our most primitive chordate relative, has long been recognized as a candidate precursor to the vertebrate eyes. However, the amphioxus frontal eye is composed of simple ciliated cells, unlike vertebrate rods and cones, which display more elaborate, surface-extended cilia. So far, the only evidence that the frontal eye indeed might be sensitive to light has been the presence of a ciliated putative sensory cell in the close vicinity of dark pigment cells. We set out to characterize the cell types of the amphioxus frontal eye molecularly, to test their possible relatedness to the cell types of vertebrate eyes. We show that the cells of the frontal eye specifically coexpress a combination of transcription factors and opsins typical of the vertebrate eye photoreceptors and an inhibitory Gi-type alpha subunit of the G protein, indicating an off-responding phototransductory cascade. Furthermore, the pigmented cells match the retinal pigmented epithelium in melanin content and regulatory signature. Finally, we reveal axonal projections of the frontal eye that resemble the basic photosensory-motor circuit of the vertebrate forebrain. These results support homology of the amphioxus frontal eye and the vertebrate eyes and yield insights into their evolutionary origin.evolution | vision | cephalochordate T he evolutionary origin of vertebrate eyes is enigmatic. Charles Darwin appreciated the conceptual difficulty in accepting that an organ as complex as the vertebrate eye could have evolved through natural selection (1). Part of the problem lies in the paucity of extant phyla with useful gradations that occurred during eye evolution, thus providing a scenario that led to the emergence of the vertebrate eye. For example, the eye of the adult lamprey (a jawless vertebrate) is remarkably similar to the eye of jawed vertebrates in the overall design, retina cell types, and multiple classes of opsins (2). Given these similarities, it is likely that the last common ancestor of jawless and jawed vertebrates already possessed an elaborate camera-type lens eye. To understand the seemingly sudden origin of the vertebrate eye, its evolutionary precursor must be identified within the nonvertebrate chordates lacking elaborated eye structures. Because of its basal phylogenetic position within the chordates (3), its slowly evolving genome (4), and its ancestral morphology, the cephalochordate amphioxus represents a traditional model organism for understanding the origin of vertebrate organs. Extensive electron microscopy studies of the cerebral vesicle of the basal chordate amphioxus revealed several putative photoreceptive organs-dorsal ocelli, Joseph cells, lamellar body, and the unpaired "frontal eye" (5). The pigmented dorsal ocelli and the Joseph cells are morphologically and molecularly related to invertebrate eye photoreceptors (6, 7), whereas the frontal eye and the lamellar body traditionally have been homologized to the vertebrate eyes and pineal g...

Animals sense light primarily by an opsin-based photopigment present in a photoreceptor cell. Cnidaria are arguably the most basal phylum containing a well-developed visual system. The evolutionary history of opsins in the animal kingdom has not yet been resolved. Here, we study the evolution of animal opsins by genome-wide analysis of the cubozoan jellyfish Tripedalia cystophora, a cnidarian possessing complex lens-containing eyes and minor photoreceptors. A large number of opsin genes with distinct tissue- and stage-specific expression were identified. Our phylogenetic analysis unequivocally classifies cubozoan opsins as a sister group to c-opsins and documents lineage-specific expansion of the opsin gene repertoire in the cubozoan genome. Functional analyses provided evidence for the use of the Gs-cAMP signaling pathway in a small set of cubozoan opsins, indicating the possibility that the majority of other cubozoan opsins signal via distinct pathways. Additionally, these tests uncovered subtle differences among individual opsins, suggesting possible fine-tuning for specific photoreceptor tasks. Based on phylogenetic, expression and biochemical analysis we propose that rapid lineage- and species-specific duplications of the intron-less opsin genes and their subsequent functional diversification promoted evolution of a large repertoire of both visual and extraocular photoreceptors in cubozoans.

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Glycodendrimers (Glyco-DDMs) represent a rapidly growing class of nanoparticles with promising properties for biomedical applications but concerns regarding the impact on human health and environment are still justified. Here we report, for the first time, the comparative study of in vivo developmental toxicity of carbosilane Glyco-DDMs and their cytotoxicity in vitro. Carbosilane Glyco-DDMs (generation 1-3) containing 4, 8, and 16 β-d-glucopyranosyl units at the periphery (DDMGlu, DDMGlu, and DDMGlu) were synthesized and characterized by H,C and Si NMR, mass spectrometry, dynamic light scattering, atomic force microscopy (AFM), and computer modeling. In vitro cytotoxicity assay (MTT) of DDMGlu was performed on three different rodent cell lines (Cricetulus griseus) - B14 (ATCC, CCL-14.1), BRL 3A (ATCC, CRL-1442), and NRK 52E (ATCC, CRL-1571). Overall, very low cytotoxicity was observed with calculated IC in mM range with slight difference between each cell line and DDM generation investigated. Modified fish embryo test (FET) was further used for DDMGlu developmental toxicity testing on zebrafish (Danio rerio) embryos. While seemingly harmless to intact embryos, adverse effects of DDMs on the embryonic development become evident after chorion removal (LD=2.78 µM at 96 hpe). We summarized that the modified FET test showed a two to three orders of magnitude difference between the in vitro cytotoxicity and in vivo developmental toxicity of DDMGlu. While, in general, the Glyco-DDMs show great promises as efficient vectors in targeted drug delivery or as therapeutic molecules itself, we suggest that their developmental toxicity should be thoroughly investigated to exclude safety risks associated with their potential biomedical use.

E-Shell 300 3D-printed material demonstrated a considerable negative impact on cell proliferation and severe developmental toxicity due to release of surfactant residues. Post-treatment with ethanol improved the biocompatibility of the material.