Biology subjects

Wilson, S. W.

Publications and source records attributed to Wilson, S. W..

15 recordsLinked to original sources

bioRxiv2026

Genetically interacting mutations and mechanical stress affect the stochasticity of developmental eye defects in yap1 mutants

Congenital abnormalities of eye formation show remarkably variable penetrance with phenotypes even varying between left and right eyes. Here we explore this phenomenon through analysis of the mechanistic basis of low penetrance retinal coloboma in zebrafish yap1nl13/nl13 mutants and identification of factors that modify the probability of this phenotype. We find that the low penetrance stochastically occurring coloboma in yap1nl13/nl13 mutants is due to rupture in the ventral retina at the point of apposition of the lips of the closing choroid fissure and that provision of wild-type Yap in the retinal pigment epithelium suppressed this phenotype. Decreasing actomyosin contractility increased the penetrance of coloboma whereas increasing myosin phosphorylation rescued the phenotype suggesting that altered mechanical properties of the RPE sensitize the eye to stochastic failure of choroid fissure closure. Genetic interaction screening revealed enhanced and synthetic eye phenotypes in yap1nl13/nl13mutants upon abrogation of function of genes encoding extracellular matrix and other genes implicated in eye formation. Our data reveal that the variable penetrance of congenital eye abnormalities can be due to genetic and environmental factors impacting the stochastic variability inherent in the developmental processes underlying eye morphogenesis.

developmental biology↗

bioRxiv2026

A novel pipeline for the validation of manganese chelators for the treatment of manganese overload

Manganese neurotoxicity, arising from environmental overexposure or inherited transporter disorders due to pathogenic variants in SLC30A10 and SLC39A14, leads to manganism, a debilitating Parkinsonian movement disorder. Alhtough chelation therapy can partially reverse neuropathology, current clinical practice relies on intravenous CaNa2EDTA, which is burdensome and poorly suited for long-term use. Consequently, there remains a significant unmet need for more effective, orally bioavailable chelators. This study aimed to establish and validate a pipeline for identifying and assessing novel ligands that attenuate manganese neurotoxicity and support preclinical translational development. Based on the structural features of manganese-based MRI contrast agents, we selected two chelators, N-picolyl-N,N',N'-trans-1,2-cyclohexylenediaminetriacetic acid (H3PyC3A) and ethylenediaminetetraacetic acid-benzothiazole aniline (H4EDTA-BTA), and their methyl ester derivatives, Me3PyC3A and Me4EDTA-BTA. These were evaluated in vivo using zebrafish (slc39a14U801/U801) and mouse (Slc30a10KO/KO) models of manganese overload. H3PyC3A and Me3PyC3A demonstrated greater manganese-mobilizing efficacy than CaNa2EDTA, improving locomotor behavior in slc39a14U801/U801 zebrafish. In Slc30a10KO/KO mice, intravenous administration confirmed selective in vivo chelation of excess manganese over physiological concentrations of zinc and copper. Although oral bioavailability was low (<1%), long-term oral administration of H3PyC3A modestly reduced liver and brain Mn accumulation, suggesting an added benefit of oral administration via gastrointestinal chelation. This integrated in vitro to in vivo pipeline provides a robust and scaleable approach for the development of next-generation Mn chelators. Slc39a14U801 loss-of-function zebrafish enable high throughput identification of candidate compounds while Slc30a10KO/KO mice offer a clinically relevant disease model for pharmacokinetic profiling and proof-of-concept validation.

pharmacology and toxicology↗

bioRxiv2022

A Drosophila glial cell atlas reveals that transcriptionally defined cell types can be morphologically diverse

Morphology is a defining feature of neuronal identity. Like neurons, glia display diverse morphologies, both across and within glial classes, but are also known to be morphologically plastic. Here, we explored the relationship between glial morphology and transcriptional signature using the Drosophila central nervous system, where glia are categorized into five main classes (outer and inner surface glia, cortex glia, ensheathing glia, and astrocytes), which show within-class morphological diversity. We analysed and validated single cell RNA sequencing data of Drosophila glia in two well-characterized tissues from distinct developmental stages, containing distinct circuit types: the embryonic ventral nerve cord (motor) and the adult optic lobes (sensory). Our analysis identified a new morphologically and transcriptionally distinct surface glial population in the ventral nerve cord. However, many glial morphological categories could not be distinguished transcriptionally, and indeed, embryonic and adult astrocytes were transcriptionally analogous despite differences in developmental stage and circuit type. While we did detect extensive within-class transcriptomic diversity for optic lobe glia, this could be explained entirely by glial residence in the most superficial neuropil (lamina) and an associated enrichment for immune-related gene expression. In summary, we generated a single-cell transcriptomic atlas of glia in Drosophila, and our extensive in vivo validation revealed that glia exhibit more diversity at the morphological level than was detectable at the transcriptional level. This atlas will serve as a resource for the community to probe glial diversity and function.

neuroscience↗

bioRxiv2022

Cachd1 is a novel Frizzled- and LRP6-interacting protein required for neurons to acquire left-right asymmetric character

Neurons on left and right sides of the nervous system frequently show asymmetric properties but how these differences arise is poorly understood. Through a forward genetic screen in zebrafish, we find that loss of function of the transmembrane protein Cachd1 results in right-sided habenula neurons adopting left-sided character. Cachd1 is expressed in habenula neuron progenitors, functions symmetrically downstream of asymmetric environmental signals that determine laterality and influences timing of the normally left-right asymmetric patterns of neurogenesis. Unbiased screening for Cachd1 partners identified the Wnt co-receptor Frizzled7 and further biochemical and structural analysis revealed Cachd1 can bind simultaneously to Fzd proteins and Lrp6, bridging between these two Wnt co-receptors. Consistent with these structural studies, lrp6 mutant zebrafish show symmetric habenulae with left-sided character and epistasis experiments with other Wnt pathway genes support an in vivo role for Cachd1 in modulating Wnt pathway activity in the brain. Together, these studies identify Cachd1 as a conserved novel Wnt-receptor interacting protein with roles in regulating neurogenesis and neuronal identity.

developmental biology↗

bioRxiv2022

Foxd1 dependent induction of temporal retinal character is required for visual function

Appropriate patterning of the retina during embryonic development is assumed to underlie the establishment of spatially localised specialisations that mediate the perception of specific visual features. For instance, in zebrafish, an area involved in high acuity vision (HAA) is thought to be present in the ventro-temporal retina. Here we show that the interplay of the transcription factor Rx3 with Fibroblast Growth Factor and Hedgehog signals, initiates and restricts foxd1 expression to the prospective temporal retina, initiating naso-temporal regionalisation of the retina. Abrogation of FoxD1 results in the loss of temporal and expansion of nasal retinal character, and consequent absence of the HAA. These structural defects correlate with severe visual defects as assessed in optokinetic and optomotor response assays. In contrast, optokinetic responses are unaffected in the opposite condition in which nasal retinal character is lost at the expense of expanded temporal character. Our study indicates that the establishment of temporal retinal character during early retinal development is required for the specification of the HAA, and suggests a prominent role of the temporal retina in controlling specific visual functions. Summary statementThis study provides a mechanistic link between eye patterning and the establishment of functionally distinct retinal regions and reveals the temporal retina preferentially controls specific aspects of visual function.

developmental biology↗

bioRxiv2022

A structural atlas of the developing zebrafish telencephalon based on spatially-restricted transgene expression

1.Zebrafish telencephalon acquires an everted morphology by a two-step process that occurs from 1 to 5 days post-fertilization (dpf). Little is known about how this process affects the positioning of discrete telencephalic cell populations, hindering our understanding of how eversion impacts telencephalic structural organisation. In this study, we characterise the neurochemistry, cycle state and morphology of an EGFP positive (+) cell population in the telencephalon of Et(gata2:EGFP)bi105 transgenic fish during eversion and up to 20dpf. We map the transgene insertion to the early-growth-response-gene-3 (egr3) locus and show that EGFP expression recapitulates endogenous egr3 expression throughout much of the pallial telencephalon. Using the gata2:EGFPbi105 transgene, in combination with other well-characterised transgenes and structural markers, we track the development of various cell populations in the zebrafish telencephalon as it undergoes the morphological changes underlying eversion. These datasets were registered to reference brains to form an atlas of telencephalic development at key stages of the eversion process (1dpf, 2dpf and 5dpf) and compared to expression in adulthood. Finally, we registered gata2:EGFPbi105 expression to the Zebrafish Brain Browser 6dpf reference brain (ZBB, see Marquart et al., 2015, 2017; Tabor et al. 2019), to allow comparison of this expression pattern with anatomical data already in ZBB.

neuroscience↗

bioRxiv2021

A red herring in zebrafish genetics: allele-specific gene expression can underlie altered transcript abundance in zebrafish mutants

In model organisms, RNA sequencing is frequently used to assess the effect of genetic mutations on cellular and developmental processes. Typically, animals heterozygous for a mutation are crossed to produce offspring with different genotypes. Resultant embryos are grouped by genotype to compare homozygous mutant embryos to heterozygous and wild-type siblings. Genes that are differentially expressed between the groups are assumed to reveal insights into the pathways affected by the mutation. Here we show that in zebrafish, differentially expressed genes are often overrepresented on the same chromosome as the mutation due to different levels of expression of alleles from different genetic backgrounds. Using an incross of haplotype-resolved wild-type fish, we found evidence of widespread allele-specific expression, which appears as differential expression when comparing embryos homozygous for a region of the genome to their siblings. When analysing mutant transcriptomes, this means that differentially expressed genes on the same chromosome as a mutation of interest may not be caused by that mutation. Typically, the genomic location of a differentially expressed gene is not considered when interpreting its importance with respect to the phenotype. This could lead to pathways being erroneously implicated or overlooked due to the noise of spurious differentially expressed genes on the same chromosome as the mutation. These observations have implications for the interpretation of RNA-seq experiments involving outbred animals and non-inbred model organisms.

developmental biology↗

bioRxiv2020

Zinc dysregulation in slc30a8 (znt8) mutant zebrafish leads to blindness and disrupts bone mineralisation

Zinc is an essential cofactor for many cellular processes including gene transcription, insulin secretion and retinal function. Excessive free Zn2+ is highly toxic and consequently intracellular zinc is tightly controlled by a system of transporters, metallothioneins (MTs) and storage vesicles. Here we describe the developmental consequences of a missense allele of zinc efflux transporter slc30a8 (znt8) in zebrafish. Homozygous slc30a8hu1798 larvae are virtually blind and develop very little or no bone mineral. We show that zinc is stored in pigmented cells (melanophores) of healthy larvae but in slc30a8hu1798 mutants it instead accumulates in the bone and brain. Supporting a role for pigment cells in zinc homeostasis, nacre zebrafish, which lack melanophores, also show disrupted zinc homeostasis. The photoreceptors of slc30a8hu1798 fish are severely depleted while those of nacre fish are enriched with zinc. We propose that developing zebrafish utilise pigmented cells as a zinc storage organ, and that Slc30a8 is required for transport of zinc into these cells and into photoreceptors.

physiology↗

bioRxiv2020

A simple and effective F0 knockout method for rapid screening of behaviour and other complex phenotypes

Hundreds of human genes are associated with neurological diseases, but translation into tractable biological mechanisms is lagging. Larval zebrafish are an attractive model to investigate genetic contributions to neurological diseases. However, current CRISPR-Cas9 methods are difficult to apply to large genetic screens studying behavioural phenotypes. To facilitate rapid genetic screening, we developed a simple sequencing-free tool to validate gRNAs and a highly effective CRISPR-Cas9 method capable of converting >90% of injected embryos directly into F0 biallelic knockouts. We demonstrate that F0 knockouts reliably recapitulate complex mutant phenotypes, such as altered molecular rhythms of the circadian clock, escape responses to irritants, and multi-parameter day-night locomotor behaviours. The technique is sufficiently robust to knockout multiple genes in the same animal, for example to create the transparent triple knockout crystal fish for imaging. Our F0 knockout method cuts the experimental time from gene to behavioural phenotype in zebrafish from months to one week.

genetics↗

bioRxiv2020

The GINS complex is required for the survival of rapidly proliferating retinal and tectal progenitor cells during zebrafish development

Efficient and accurate DNA replication is particularly critical in stem and progenitor cells for successful proliferation and survival. The replisome, an amalgam of protein complexes, is responsible for binding potential origins of replication, unwinding the double helix, and then synthesizing complimentary strands of DNA. According to current models, the initial steps of DNA unwinding and opening are facilitated by the CMG complex, which is composed of a GINS heterotetramer that connects Cdc45 with the mini-chromosome maintenance (Mcm) helicase. In this work, we provide evidence that in the absence of GINS function DNA replication is cell autonomously impaired, and we also show that gins1 and gins2 mutants exhibit elevated levels of apoptosis restricted to actively proliferating regions of the central nervous system (CNS). Intriguingly, our results also suggest that the rapid cell cycles during early embryonic development in zebrafish may not require the function of the GINS complex as neither Gins1 nor Gins2 seem to be present during these stages.

genetics↗

bioRxiv2020

Loss of slc39a14 causes simultaneous manganese deficiency and hypersensitivity in zebrafish

Mutations in SLC39A14, a manganese uptake transporter, lead to a neurodegenerative disorder characterised by accumulation of manganese in the brain and rapidly progressive dystonia-parkinsonism (Hypermanganesemia with Dystonia 2, HMNDYT2). Similar to the human phenotype, zebrafish slc39a14U801-/- mutants show prominent brain manganese accumulation and abnormal locomotor behaviour. In order to identify novel potential targets of manganese neurotoxicity, we performed transcriptome analysis of individual homozygous mutant and sibling slc39a14U801 zebrafish at five days post fertilisation unexposed and exposed to MnCl2. Anatomical gene enrichment analysis confirmed that differentially expressed genes map to the central nervous system and eye. Biological interpretation of differentially expressed genes suggests that calcium dyshomeostasis, activation of the unfolded protein response, oxidative stress, mitochondrial dysfunction, lysosomal disruption, apoptosis and autophagy, and interference with proteostasis are key events in manganese neurotoxicity. Differential expression of visual phototransduction genes also predicted visual dysfunction in mutant larvae which was confirmed by the absence of visual background adaptation and a diminished optokinetic reflex. Surprisingly, we found a group of differentially expressed genes in mutant larvae that normalised upon MnCl2 treatment suggesting that, in addition to neurotoxicity, manganese deficiency is present either subcellularly or in specific cells or tissues. This may have important implications for treatment as manganese chelation may aggravate neurological symptoms. Our analyses show that slc39a14U801-/- mutant zebrafish present a powerful model to study the cellular and molecular mechanisms underlying disrupted manganese homeostasis. Significance statementManganese neurotoxicity leading to progressive dystonia-parkinsonism is a characteristic feature of Hypermanganesemia with dystonia 2 (HMNDYT2) caused by mutations in SLC39A14, a manganese uptake transporter. Transcriptional profiling in slc39a14U801 loss-of-function zebrafish suggests that, in addition to manganese neurotoxicity, subcellular or cell type specific manganese deficiency contributes to the disease phenotype. Both manganese overload and deficiency appear to be associated with Ca2+ dyshomeostasis. We further demonstrate that activation of the unfolded protein response, oxidative stress, mitochondrial dysfunction, apoptosis and autophagy, and disrupted proteostasis are likely downstream events in manganese neurotoxicity. Our study shows that the zebrafish slc39a14U801 loss-of-function mutant is a powerful model to elucidate the mechanistic basis of diseases affected by manganese dyshomeostasis.

neuroscience↗

bioRxiv2019

Developmentally regulated tcf7l2 splice variants mediate transcriptional repressor functions during eye formation

Tcf7l2 mediates Wnt/{beta}-Catenin signalling during development and is implicated in cancer and type-2 diabetes. The mechanisms by which Tcf7l2 and Wnt/{beta}-Catenin signalling elicits such a diversity of biological outcomes are poorly understood. Here, we study alternatively spliced tcf7l2 in zebrafish and show that only splice variants that include exon 5 and an analogous human tcf7l2 variant can effectively provide compensatory repressor function to restore eye formation in embryos lacking tcf7l1a/tcf7l1b function. Knockdown of exon 5 specific tcf7l2 variants in tcf7l1a mutants also compromises eye formation and these variants can effectively repress Wnt pathway activity in reporter assays using Wnt target gene promoters. We show that the repressive activities of exon5-coded variants are likely explained by their interaction with Tle co-repressors. Furthermore, phosphorylated residues in Tcf7l2 coded exon5 facilitate repressor activity. Our studies suggest that developmentally regulated splicing of tcf7l2 can influence the transcriptional output of the Wnt pathway.

developmental biology↗

bioRxiv2019

Sox1a mediates the ability of the parapineal to impart habenular left-right asymmetry

Left-right asymmetries in the zebrafish habenular nuclei are dependent upon the formation of the parapineal, a unilateral group of neurons that arise from the medially positioned pineal complex. In this study, we show that both the left and right habenula are competent to adopt left-type molecular character and efferent connectivity upon the presence of only a few parapineal cells. This ability to impart left-sided character is lost in parapineal cells lacking Sox1a function, despite the normal specification of the parapineal itself. Precisely timed laser ablation experiments demonstrate that the parapineal influences neurogenesis in the left habenula at early developmental stages as well as neurotransmitter phenotype and efferent connectivity during subsequent stages of habenular differentiation. These studies reveal a tight coordination between the formation of the unilateral parapineal nucleus and emergence of asymmetric habenulae, ensuring that appropriate lateralised character is propagated within left and right-sided circuitry.

developmental biology↗

bioRxiv2018

Abrogation of Stem Loop Binding Protein (Slbp) function leads to a failure of cells to transition from proliferation to differentiation, retinal coloboma and midline axon guidance deficits.

Through forward genetic screening for mutations affecting visual system development, we identified prominent coloboma and cell-autonomous retinal neuron differentiation, lamination and retinal axon projection defects in eisspalte (ele) mutant zebrafish. Additional axonal deficits were present, most notably at midline axon commissures. Genetic mapping and cloning of the ele mutation showed that the affected gene is slbp, which encodes a conserved RNA stem-loop binding protein involved in replication dependent histone mRNA metabolism. Cells throughout the central nervous system remained in the cell cycle in ele mutant embryos at stages when, and locations where, post-mitotic cells have differentiated in wild-type siblings. Indeed, RNAseq analysis showed down-regulation of many genes associated with neuronal differentiation. This was coincident with changes in the levels and spatial localisation of expression of various genes implicated, for instance, in axon guidance, that likely underlie specific ele phenotypes. These results suggest that many of the cell and tissue specific phenotypes in ele mutant embryos are secondary to altered expression of modules of developmental regulatory genes that characterise, or promote transitions in, cell state and require the correct function of Slbp-dependent histone and chromatin regulatory genes.\n\nAuthor SummaryCongenital deficits of eye formation are common in humans and to help understand the genetic basic of such conditions, we are studying zebrafish with comparable eye defects. We identified defects in both the shaping of the eye and in its connections to the brain in eisspalte mutant fish. Further analyses revealed additional deficits in the brain, most notably a severe reduction in neurons and their connections. We find that this is due to an inability of the cells that generate neurons to transition from proliferation to neuronal differentiation. By using a sequencing approach to compare mutant embryos to their normal siblings, we identified the affected gene as slbp, which encodes a protein that binds the mRNAs of other genes important for cell proliferation. This sequencing approach revealed the full extent of changes in gene expression in the mutant, helping us to better understand why the nervous system defects occur. Our study suggests that in the absence of Slbp function, cells lose the ability to transition from the proliferative to the differentiated state and this leads to additional defects in the eyes and brain.

genetics↗

bioRxiv2018

Compensatory mechanisms render Tcf7l1a dispensable for eye formation despite its requirement in eye field specification

The vertebrate eye originates from the eyefield, a domain of cells specified by a small number of transcription factors. In this study, we show that Tcf7la is one such transcription factor that acts cell-autonomously to specify the eye field in zebrafish. Despite the much reduced eyefield in tcf7l1a mutants, these fish develop normal eyes revealing a striking ability of the eye to recover from a severe early phenotype. This robustness is not mediated through compensation by paralogous genes; instead, the smaller optic vesicle of tcf7l1a mutants shows delayed neurogenesis and continues to grow until it achieves approximately normal size. Although the developing eye is robust to the lack of Tcf7l1a function, it is sensitised to the effects of additional mutations. In support of this, a forward genetic screen identified mutations in hesx1, cct5 and gdf6a, which give synthetically enhanced eye specification or growth phenotypes when in combination with the tcf7l1a mutation.

developmental biology↗