Zebrafish Retina Research Articles

Eye flukes (Diplostomum spp) damage retinal tissue and may cause a regenerative response in wild threespine stickleback fish.

Fish rely upon vision as a dominant sensory system for foraging, predator avoidance, and mate selection. Damage to the visual system, in particular to the neural retina of the eye, has been demonstrated to result in a regenerative response in captive fish that serve as model organisms (e.g. zebrafish), and this response restores some visual function. The purpose of the present study is to determine whether damage to the visual system that occurs in wild populations of fish also results in a regenerative response, offering a potentially ecologically relevant model of retinal regeneration. Adult threespine stickleback were collected from several water bodies of Iceland, and cryosectioned eye tissues were processed for hematoxylin and eosin staining or for indirect immunofluorescence using cell-specific markers. In many of the samples, eye flukes (metacercariae of Diplostomum spp) were present, frequently between the neural retina and retinal pigmented epithelium (RPE). Damage to the retina and to the RPE was evident in eyes containing flukes, and RPE fragments were observed within fluke bodies, suggesting they had consumed this eye tissue. Expression of a cell proliferation marker was also observed in both retina and RPE, consistent with a proliferative response to the damage. Interestingly, some regions of infected retina displayed "laminar fusions," in which neuronal cell bodies were misplaced within the major synaptic layer of the retina. These laminar fusions are also frequently found in regenerated zebrafish retina following non-parasitic (experimental) forms of retinal damage. The stickleback retina may therefore respond to fluke-mediated damage by engaging in retinal regeneration.

Tulp1 deficiency causes early-onset retinal degeneration through affecting ciliogenesis and activating ferroptosis in zebrafish

Mutations in TUB-like protein 1 (TULP1) are associated with severe early-onset retinal degeneration in humans. However, the pathogenesis remains largely unknown. There are two homologous genes of TULP1 in zebrafish, namely tulp1a and tulp1b. Here, we generated the single knockout (tulp1a−/− and tulp1b−/−) and double knockout (tulp1-dKO) models in zebrafish. Knockout of tulp1a resulted in the mislocalization of UV cone opsins and the degeneration of UV cones specifically, while knockout of tulp1b resulted in mislocalization of rod opsins and rod-cone degeneration. In the tulp1-dKO zebrafish, mislocalization of opsins was present in all types of photoreceptors, and severe degeneration was observed at a very early age, mimicking the clinical manifestations of TULP1 patients. Photoreceptor cilium length was significantly reduced in the tulp1-dKO retinas. RNA-seq analysis showed that the expression of tektin2 (tekt2), a ciliary and flagellar microtubule structural component, was downregulated in the tulp1-dKO zebrafish. Dual-luciferase reporter assay suggested that Tulp1a and Tulp1b transcriptionally activate the promoter of tekt2. In addition, ferroptosis might be activated in the tulp1-dKO zebrafish, as suggested by the up-regulation of genes related to the ferroptosis pathway, the shrinkage of mitochondria, reduction or disappearance of mitochondria cristae, and the iron and lipid droplet deposition in the retina of tulp1-dKO zebrafish. In conclusion, our study establishes an appropriate zebrafish model for TULP1-associated retinal degeneration and proposes that loss of TULP1 causes defects in cilia structure and opsin trafficking through the downregulation of tekt2, which further increases the death of photoreceptors via ferroptosis. These findings offer insight into the pathogenesis and clinical treatment of early-onset retinal degeneration.

A theoretical model reveals specialized synaptic depressions and temporal frequency tuning in retinal parallel channels.

In the Outer Plexiform Layer of a retina, a cone pedicle provides synaptic inputs for multiple cone bipolar cell (CBC) subtypes so that each subtype formats a parallelized processing channel to filter visual features from the environment. Due to the diversity of short-term depressions among cone-CBC contacts, these channels have different temporal frequency tunings. Here, we propose a theoretical model based on the hierarchy Linear-Nonlinear-Synapse framework to link the synaptic depression and the neural activities of the cone-CBC circuit. The model successfully captures various frequency tunings of subtype-specialized channels and infers synaptic depression recovery time constants inside circuits. Furthermore, the model can predict frequency-tuning behaviors based on synaptic activities. With the prediction of region-specialized UV cone parallel channels, we suggest the acute zone in the zebrafish retina supports detecting light-off events at high temporal frequencies.

Chromatin remodeler Chd7 regulates photoreceptor development and outer segment length

Mutations in the chromatin remodeling factor CHD7 are the predominant cause of CHARGE syndrome, a congenital disorder that frequently includes ocular coloboma. Although CHD7 is known to be required for proper ocular morphogenesis, its role in retinal development has not been thoroughly investigated. Given that individuals with CHARGE syndrome can experience visual impairment even in the absence of coloboma, a better understanding of CHD7 function in the retina is needed. In this study, we characterized the expression pattern of Chd7 in the developing zebrafish and mouse retina and documented ocular and retinal phenotypes in Chd7 loss-of-function mutants. Zebrafish Chd7 was expressed throughout the retinal neuroepithelium when retinal progenitor cells were actively proliferating, and later in subsets of newly post-mitotic retinal cells. At stages of retinal development when most retinal cell types had terminally differentiated, Chd7 expression remained strong in the ganglion cell layer and in some cells in the inner nuclear layer. Intriguingly, strong expression of Chd7 was also observed in the outer nuclear layer where it was co-expressed with markers of post-mitotic cone and rod photoreceptors. Expression of mouse CHD7 displayed a similar pattern, including expression in the ganglion cells, subsets of inner nuclear layer cells, and in the distal outer nuclear layer as late as P15. Two different mutant chd7 zebrafish lines were characterized for ocular and retinal defects. These mutants displayed microphthalmia, reduced numbers of cone photoreceptors, and truncated rod and cone photoreceptor outer segments. Reduced cone photoreceptor number and abnormal outer segments were also observed in heterozygous Chd7 mutant mice. Taken together, our results in zebrafish and mouse reveal a conserved, previously undescribed role for Chd7 in retinal development and photoreceptor outer segment morphogenesis. Moreover, our work suggests an avenue of future investigation into the pathogenesis of visual system defects in CHARGE syndrome.

Data-Driven Models of Efficient Chromatic Coding in the Outer Retina.

Recent experimental work on zebrafish has shown the in vivo activity of photoreceptors and horizontal cells (HCs) as a function of the stimulus spectrum, highlighting the appearance of chromatic-opponent signals at their first synaptic connection. Altogether with the observed lack of excitatory intercone connections, these findings suggest that the mechanism yielding early color opponency in zebrafish is dominated by inhibitory feedback. We propose a neuronal population model based on zebrafish retinal circuitry to investigate whether networks with predominantly inhibitory feedback are more advantageous in encoding chromatic information than networks with mixed excitatory and inhibitory mechanisms. We show that networks with dominant inhibitory feedback exhibit a unique and reliable encoding of chromatic information. In contrast, this property is not guaranteed in networks with strong excitatory intercone connections, exhibiting bistability. These findings provide a theoretical explanation for the absence of excitatory intercone couplings in zebrafish color circuits. In addition, our study shows that these networks, with only one type of horizontal cell, are suitable to encode most of the variance from the zebrafish environment. However, at least two successive layers of inhibitory neurons are needed to reach the optimum. Finally, we contrast the encoding performance of networks with different opsin sensitivities, showing an improvement of only 13% compared with zebrafish, suggesting that the zebrafish retina is adapted to encode color information from its habitat efficiently.

Facile synthesis of ultrabright luminogens with specific lipid droplets targeting feature for in vivo two-photon fluorescence retina imaging

The application of fluorescent probes for in vivo retinal imaging is of great importance, which could provide direct and crucial imaging evidence for a better understanding of common eye diseases. Herein, a group of bright organic luminogens with typical electron-donating (D) and electron-accepting (A) structures (abbreviated as LDs-BDM, LDs-BTM, and LDs-BHM) was synthesized through a simple single-step reaction. They were found to be efficient solid-state emitters with high fluorescence quantum yields of above 70% (e.g., 83.7% for LDs-BTM). Their light-emission properties could be tuned by the modulation of π-conjugation effect with methoxy groups at different substituent positions. Their resulting fluorescent nanoparticles (NPs) were demonstrated as specific lipid droplets (LDs) targeting probes with high brightness, good biocompatibility, and satisfactory photostability. LDs-BTM NPs with a large two-photon absorption cross section (σ2 = 249 GM) were further utilized as ultrabright two-photon fluorescence (2PF) nanoprobes for in vivo retina imaging of live zebrafish by NIR excitation at an ultralow concentration (0.5 µmol/L). Integrated histological structures at the tissue level and corresponding fine details at the cellular level of the embryonic retina of live zebrafish were clearly demonstrated. This is the first report of using ultrabright LDs-targeting nanoprobes to accurately measure fine details in the retina with 2PF microscopic technique. These good results are anticipated to open up a new avenue in the development of efficient 2PF emitters for non-invasive bioimaging of living animals.

Pten associates with important gene regulatory network to fine-tune Müller glia-mediated zebrafish retina regeneration.

Unlike mammals, zebrafish possess a remarkable ability to regenerate damaged retina after an acute injury. Retina regeneration in zebrafish involves the induction of Müller glia-derived progenitor cells (MGPCs) exhibiting stem cell-like characteristics, which are capable of restoring all retinal cell-types. The induction of MGPC through Müller glia-reprograming involves several cellular, genetic and biochemical events soon after a retinal injury. Despite the knowledge on the importance of Phosphatase and tensin homolog (Pten), which is a dual-specificity phosphatase and tumor suppressor in the maintaining of cellular homeostasis, its importance during retina regeneration remains unknown. Here, we explored the importance of Pten during zebrafish retina regeneration. The Pten gets downregulated upon retinal injury and is absent from the MGPCs, which is essential to trigger Akt-mediated cellular proliferation essential for retina regeneration. We found that the downregulation of Pten in the post-injury retina accelerates MGPCs formation, while its overexpression restricts the regenerative response. We observed that Pten regulates the proliferation of MGPCs not only through Akt pathway but also by Mmp9/Notch signaling. Mmp9-activity is essential to induce the proliferation of MGPCs in the absence of Pten. Lastly, we show that expression of Pten is fine-tuned through Mycb/histone deacetylase1 and Tgf-β signaling. The present study emphasizes on the stringent regulation of Pten and its crucial involvement during the zebrafish retina regeneration.

Spatial regulation of amacrine cell genesis by Semaphorin 3f

PurposeThe axonal projections of retinal ganglion cells (RGCs) of the eye are topographically organized so that spatial information from visual images is preserved. This retinotopic organization is established during development by secreted morphogens that pattern domains of transcription factor expression within naso-temporal and dorso-ventral quadrants of the embryonic eye. Poorly understood are the downstream signaling molecules that generate the topographically organized retinal cells and circuits. The secreted signaling molecule Semaphorin 3fa (Sema3fa) belongs to the Sema family of molecules that provide positional information to developing cells. Here, we test a role for Sema3fa in cell genesis of the temporal zebrafish retina. MethodsWe compare retinal cell genesis in wild type and sema3fa CRISPR zebrafish mutants by in situ hybridization and immunohistochemistry. ResultsWe find that mRNAs for sema3fa and known receptors, neuropilin2b (nrp2b) and plexina1a (plxna1a), are expressed by progenitors of the temporal, but not nasal zebrafish embryonic retina. In the sema3faca304/ca304 embryo, initially the domains of expression for atoh7 and neurod4, transcription factors necessary for the specification of RGCs and amacrine cells, respectively, are disrupted. Yet, post-embryonically only amacrine cells of the temporal retina are reduced in numbers, with both GABAergic and glycinergic subtypes affected. ConclusionsThese data suggest that Sema3fa acts early on embryonic temporal progenitors to control in a spatially-dependent manner the production of amacrine cells, possibly to allow the establishment of neural circuits with domain-specific functions. We propose that spatially restricted extrinsic signals in the neural retina control cell genesis in a domain-dependent manner.

Jag2b-Notch3/1b-mediated neuron-to-glia crosstalk controls retinal gliogenesis.

In the developing central nervous systems (CNS), neural progenitor cells generate neurons and glia in sequential order. However, the influence of neurons on glia generation remains elusive. Here, we report that photoreceptor cell-derived Jag2b is required for Notch-dependent Müller glia (MG) generation in the developing zebrafish retina. In jab2b-/- mutants, differentiating MGs are re-specified into lineage-related bipolar neuron fate at the expense of mature MG. Single-cell transcriptome analysis and knock-in animals reveal that jab2b is specifically expressed in crx+ -photoreceptor cells during MG generation. Crx promoter-driven jag2b, but not other Notch ligands, is sufficient to rescue the loss of MGs observed in jag2b-/- mutants. Furthermore, we observe a severe and moderate decrease in the number of MGs in notch3-/- and notch1b-/- mutants, respectively, and the activation of Notch3 or Notch1b rescues the MG loss in jag2b-/- mutants. Together, our findings reveal that the interaction of Jag2b and Notch3/Notch1b mediates the crosstalk between neurons and glial cells to ensure the irreversible differentiation of MG, providing novel mechanistic insights into the temporal specification of glial cell fate in a developing vertebrate CNS structure.

Different inflammation responses modulate Müller glia proliferation in the acute or chronically damaged zebrafish retina.

Unlike mammals, zebrafish regenerate in response to retinal damage. Because microglia are activated by retinal damage, we investigated their role during regeneration following either acute or chronic damage. At three weeks post-fertilization (wpf), both wild-type fish exhibiting NMDA-induced acute ganglion and amacrine cell death and gold rush (gosh) mutant fish possessing chronic cone photoreceptor degeneration displayed reactive microglia/macrophages and Müller glia proliferation. Dexamethasone-treated retinas, to inhibit the immune response, lacked reactive microglia/macrophages and possessed fewer PCNA-positive cells, while LPS treatment increased microglia/macrophages and PCNA-labeled cells. NMDA-injured retinas upregulated expression of il-1β and tnfα pro-inflammatory cytokine genes, followed by increased expression of il-10 and arg1 anti-inflammatory/remodeling cytokine genes. A transient early TNFα pro-inflammatory microglia/macrophage population was visualized in NMDA-damaged retinas. In contrast, gosh mutant retinas exhibited a slight increase of pro-inflammatory cytokine gene expression concurrently with a greater increased anti-inflammatory/remodeling cytokine gene expression. Few TNFα pro-inflammatory microglia/macrophages were observed in the gosh retina. Understanding why acute and chronic damage results in different inflammation profiles and their effects on regulating zebrafish retinal regeneration would provide important clues toward improving therapeutic strategies for repairing injured mammalian tissues.

Time dependent effects of prolonged hyperglycemia in zebrafish brain and retina.

Prolonged hyperglycemia causes long-term vision complications and an increased risk of cognitive deficits. High blood sugar also confers an osmotic load/stress to cells. We assessed behavioral and neurochemical changes in zebrafish brain and retina following prolonged hyperglycemia for 4-weeks or 8-weeks. At each time point, behavior was assessed using 3-chamber choice task and optomotor response; tissue was then collected and levels of inflammatory markers, tight junction proteins, and neurotransmitters determined using Western Blots. After 4-weeks, brain levels of v-rel reticuloendotheliosis viral oncogene homolog A (avian) (RelA; NF-kB subunit), IkB kinase (IKK), and glial fibrillary acidic protein (GFAP) were significantly elevated; differences in zonula occludens-1 (ZO-1), claudin-5, glutamic acid decarboxylase (GAD), and tyrosine hydroxylase (TH) were not significant. In retina, significant differences were observed only for TH (decreased), Rel A (increased), and GFAP (increased) levels. Glucose-specific differences in initial choice latency and discrimination ratios were also observed. After 8-weeks, RelA, GAD, and TH were significantly elevated in both tissues; IKK and GFAP levels were also elevated, though not significantly. ZO-1 and claudin-5 levels osmotically decreased in retina but displayed an increasing trend in glucose-treated brains. Differences in discrimination ratio were driven by osmotic load. OMRs increased in glucose-treated fish at both ages. In vivo analysis of retinal vasculature suggested thicker vessels after 4-weeks, but thinner vessels at 8-weeks. In vitro, glucose treatment reduced formation of nodes and meshes in 3B-11 endothelial cells, suggesting a reduced ability to form a vascular network. Overall, hyperglycemia triggered a strong inflammatory response causing initial trending changes in tight junction and neuronal markers. Most differences after 4-weeks of exposure were observed in glucose-treated fish suggesting effects on glucose metabolism independent of osmotic load. After 8-weeks, the inflammatory response remained and glucose-specific effects on neurotransmitter markers were observed. Osmotic differences impacted cognitive behavior and retinal protein levels; protein levels in brain displayed glucose-driven changes. Thus, we not only observed differential sensitivities of retina and brain to glucose-insult, but also different cellular responses, suggesting hyperglycemia causes complex effects at the cellular level and/or that zebrafish are able to compensate for the continued high blood glucose levels.

Banp regulates DNA damage response and chromosome segregation during the cell cycle in zebrafish retina.

Btg3-associated nuclear protein (Banp) was originally identified as a nuclear matrix-associated region (MAR)-binding protein and it functions as a tumor suppressor. At the molecular level, Banp regulates transcription of metabolic genes via a CGCG-containing motif called the Banp motif. However, its physiological roles in embryonic development are unknown. Here, we report that Banp is indispensable for the DNA damage response and chromosome segregation during mitosis. Zebrafish banp mutants show mitotic cell accumulation and apoptosis in developing retina. We found that DNA replication stress and tp53-dependent DNA damage responses were activated to induce apoptosis in banp mutants, suggesting that Banp is required for regulation of DNA replication and DNA damage repair. Furthermore, consistent with mitotic cell accumulation, chromosome segregation was not smoothly processed from prometaphase to anaphase in banp morphants, leading to a prolonged M-phase. Our RNA- and ATAC-sequencing identified 31 candidates for direct Banp target genes that carry the Banp motif. Interestingly, a DNA replication fork regulator, wrnip1, and two chromosome segregation regulators, cenpt and ncapg, are included in this list. Thus, Banp directly regulates transcription of wrnip1 for recovery from DNA replication stress, and cenpt and ncapg for chromosome segregation during mitosis. Our findings provide the first in vivo evidence that Banp is required for cell-cycle progression and cell survival by regulating DNA damage responses and chromosome segregation during mitosis.

Inhibition of BRD4 Attenuates Inflammation and Oxidative Stress in Retina

To determine how oxidative stress in the zebrafish retina alters the expression of genes linked with stress pathways and how different inhibitors compare in their effectiveness in suppressing damage linked with specific cellular processes.

Affinity purification of in vivo assembled whirlin-associated protein complexes from the zebrafish retina

Mutations in WHRN lead to Usher syndrome type 2d or to non-syndromic hearing impairment. The WHRN-encoded gene product whirlin directly interacts with the intracellular regions of the other two Usher syndrome type 2-associated proteins, usherin and ADGRV1. In photoreceptor cells, this protein complex constitutes fibrous links between the periciliary membrane and the connecting cilium. However, the molecular mechanism(s) of retinal degeneration due to compromised formation and function of the USH2-associated protein complex remains elusive. To unravel this pathogenic mechanism, we isolated and characterized whirlin-associated protein complexes from zebrafish photoreceptor cells. We generated transgenic zebrafish that express Strep/FLAG-tagged Whrna, a zebrafish ortholog of human whirlin, under the control of a photoreceptor-specific promoter. Affinity purification of Strep/FLAG-tagged Whrna and associated proteins from adult transgenic zebrafish retinas followed by mass spectrometry identified 19 novel candidate associated proteins. Pull down experiments and dedicated yeast two-hybrid assays confirmed the association of Whrna with 7 of the co-purified proteins. Several of the co-purified proteins are part of the synaptic proteome, which indicates a role for whirlin in the photoreceptor synapse. Future studies will elucidate which of the newly identified protein-protein interactions contribute to the development of the retinal phenotype observed in USH2d patients. SignificanceSince protein-protein interactions identified using targeted in vitro studies do not always recapitulate interactions that are functionally relevant in vivo, we established a transgenic zebrafish line that stably expresses a Strep/FLAG-tagged ortholog of human whirlin (SF-Whrna) in photoreceptor cells. Affinity purification of in vivo-assembled SF-Whrna-associated protein complexes from retinal lysates followed by mass spectrometry, identified 19 novel candidate interaction partners, many of which are enriched in the synaptic proteome. Two human orthologs of the identified candidate interaction partners, FRMPD4 and Kir2.3, were validated as direct interaction partners of human whirlin using a yeast two-hybrid assay. The strong connection of whirlin with postsynaptic density proteins was not identified in previous in vitro protein-protein interaction assays, presumably due to the absence of a biologically relevant context. Isolation and identification of in vivo-assembled whirlin-associated protein complexes from the tissue of interest is therefore a powerful methodology to obtain novel insight into tissue specific protein-protein interactions and has the potential to improve significantly our understanding of the function of whirlin and the molecular pathogenesis underlying Usher syndrome type 2.

Embryonic nutritional hyperglycemia decreases cell proliferation in the zebrafish retina.

Diabetic retinopathy (DR) is one of the leading causes of blindness in the world. While there is a major focus on the study of juvenile/adult DR, the effects of hyperglycemia during early retinal development are less well studied. Recent studies in embryonic zebrafish models of nutritional hyperglycemia (high-glucose exposure) have revealed that hyperglycemia leads to decreased cell numbers of mature retinal cell types, which has been related to a modest increase in apoptotic cell death and altered cell differentiation. However, how embryonic hyperglycemia impacts cell proliferation in developing retinas still remains unknown. Here, we exposed zebrafish embryos to 50mM glucose from 10h postfertilization (hpf) to 5days postfertilization (dpf). First, we confirmed that hyperglycemia increases apoptotic death and decreases the rod and Müller glia population in the retina of 5-dpf zebrafish. Interestingly, the increase in cell death was mainly observed in the ciliary marginal zone (CMZ), where most of the proliferating cells are located. To analyze the impact of hyperglycemia in cell proliferation, mitotic activity was first quantified using pH3 immunolabeling, which revealed a significant decrease in mitotic cells in the retina (mainly in the CMZ) at 5 dpf. A significant decrease in cell proliferation in the outer nuclear and ganglion cell layers of the central retina in hyperglycemic animals was also detected using the proliferation marker PCNA. Overall, our results show that nutritional hyperglycemia decreases cellular proliferation in the developing retina, which could significantly contribute to the decline in the number of mature retinal cells.

Comparison of the Response to the CXCR4 Antagonist AMD3100 during the Development of Retinal Organoids Derived from ES Cells and Zebrafish Retina.

Retinal organoids generated from human embryonic stem cells or iPSCs recreate the key structural and functional features of mammalian retinal tissue in vitro. However, the differences in the development of retinal organoids and normal retina in vivo are not well defined. Thus, in the present study, we analyzed the development of retinal organoids and zebrafish retina after inhibition of CXCR4, a key role in neurogenesis and optic nerve development, with the antagonist AMD3100. Our data indicated that CXCR4 was mainly expressed in ganglion cells in retinal organoids and was rarely expressed in amacrine or photoreceptor cells. AMD3100 treatment reduced the retinal organoid generation ratio, impaired differentiation, and induced morphological changes. Ganglion cells, amacrine cells, and photoreceptors were decreased and abnormal locations were observed in organoids treated with AMD3100. Neuronal axon outgrowth was also damaged in retinal organoids. Similarly, a decrease of ganglion cells, amacrine cells, and photoreceptors and the distribution of neural outgrowth was induced by AMD3100 treatment in zebrafish retina. However, abnormal photoreceptor ensembles induced by AMD3100 treatment in the organoids were not detected in zebrafish retina. Therefore, our study suggests that although retinal organoids might provide a reliable model for reproducing a retinal developmental model, there is a difference between the organoids and the retina in vivo.

Vision-related convergent gene losses reveal SERPINE3's unknown role in the eye.

Despite decades of research, knowledge about the genes that are important for development and function of the mammalian eye and are involved in human eye disorders remains incomplete. During mammalian evolution, mammals that naturally exhibit poor vision or regressive eye phenotypes have independently lost many eye-related genes. This provides an opportunity to predict novel eye-related genes based on specific evolutionary gene loss signatures. Building on these observations, we performed a genome-wide screen across 49 mammals for functionally uncharacterized genes that are preferentially lost in species exhibiting lower visual acuity values. The screen uncovered several genes, including SERPINE3, a putative serine proteinase inhibitor. A detailed investigation of 381 additional mammals revealed that SERPINE3 is independently lost in 18 lineages that typically do not primarily rely on vision, predicting a vision-related function for this gene. To test this, we show that SERPINE3 has the highest expression in eyes of zebrafish and mouse. In the zebrafish retina, serpine3 is expressed in Müller glia cells, a cell type essential for survival and maintenance of the retina. A CRISPR-mediated knockout of serpine3 in zebrafish resulted in alterations in eye shape and defects in retinal layering. Furthermore, two human polymorphisms that are in linkage with SERPINE3 are associated with eye-related traits. Together, these results suggest that SERPINE3 has a role in vertebrate eyes. More generally, by integrating comparative genomics with experiments in model organisms, we show that screens for specific phenotype-associated gene signatures can predict functions of uncharacterized genes.

Microplastics- and copper-induced changes in neurogenesis and DNA methyltransferases in the early life stages of zebrafish

In this study, zebrafish embryos were exposed to microplastics (MPs, 2 mg/L) and copper (Cu, 60 and 125 μg/L), alone or combined, for 14 days, and the development of motor neurons was assessed through gene expression and immunohistochemistry. DNA methyltransferases (DNMTs) genes expression was also evaluated.The results showed a downregulation of neuronal proliferation (sox2, pcna), neurogenesis (neuroD, olig2), and motor neurons development (islet) related genes, implying potential deficits in the neurogenesis of the exposed zebrafish early life stages. Downregulation of the maintenance and de novo DNMTs expression was also found, indicating that the DNA methylation patterns could be modulated by MPs and Cu. A high relative volume of proliferating cell nuclear antigen (PCNA)-positive cells was found in the fish retina from the MPs exposed group, suggesting that MPs increased the rate of cellular division. In contrast, a significant decrease of PCNA-positive cells, and therefore a lower cell proliferation, was found in the retina and brain of zebrafish exposed to Cu and Cu + MPs, which could lead to cognitive and behavioral functions impairment. No alterations were found in the relative volume of ISL1&2-positive cells. This study contributes to the knowledge of the mechanisms by which MPs and Cu cause neurotoxicity, fundamental for a comprehensive and realistic ecological risk assessment in aquatic populations.

Amoeboid-like migration ensures correct horizontal cell layer formation in the developing vertebrate retina.

Migration of cells in the developing brain is integral for the establishment of neural circuits and function of the central nervous system. While migration modes during which neurons employ predetermined directional guidance of either preexisting neuronal processes or underlying cells have been well explored, less is known about how cells featuring multipolar morphology migrate in the dense environment of the developing brain. To address this, we here investigated multipolar migration of horizontal cells in the zebrafish retina. We found that these cells feature several hallmarks of amoeboid-like migration that enable them to tailor their movements to the spatial constraints of the crowded retina. These hallmarks include cell and nuclear shape changes, as well as persistent rearward polarization of stable F-actin. Interference with the organization of the developing retina by changing nuclear properties or overall tissue architecture hampers efficient horizontal cell migration and layer formation showing that cell-tissue interplay is crucial for this process. In view of the high proportion of multipolar migration phenomena observed in brain development, the here uncovered amoeboid-like migration mode might be conserved in other areas of the developing nervous system.

Diurnal changes in the efficiency of information transmission at a sensory synapse

Neuromodulators adapt sensory circuits to changes in the external world or the animal’s internal state and synapses are key control sites for such plasticity. Less clear is how neuromodulation alters the amount of information transmitted through the circuit. We investigated this question in the context of the diurnal regulation of visual processing in the retina of zebrafish, focusing on ribbon synapses of bipolar cells. We demonstrate that contrast-sensitivity peaks in the afternoon accompanied by a four-fold increase in the average Shannon information transmitted from an active zone. This increase reflects higher synaptic gain, lower spontaneous “noise” and reduced variability of evoked responses. Simultaneously, an increase in the probability of multivesicular events with larger information content increases the efficiency of transmission (bits per vesicle) by factors of 1.5-2.7. This study demonstrates the multiplicity of mechanisms by which a neuromodulator can adjust the synaptic transfer of sensory information.