Now showing 1 - 10 of 33
  • Publication
    Investigation of the role of cysteinyl leukotrienes in ocular developmental angiogenesis
    Previously, we identified quininib (2-[(E)-2-(quinolin-2-yl)vinyl] phenol) and a related series of cysteinyl leukotriene (cysLT) receptor antagonists which inhibit hyaloid vessel development in zebrafish eyes. Here, we more comprehensively characterise the expression and function of specific cysLT signalling components in ocular developmental angiogenesis.
  • Publication
    Genes and signaling networks regulated during zebrafish optic vesicle morphogenesis
    Background: The genetic cascades underpinning vertebrate early eye morphogenesis are poorly understood. One gene family essential for eye morphogenesis encodes the retinal homeobox (Rx) transcription factors. Mutations in the human retinal homeobox gene (RAX) can lead to gross morphological phenotypes ranging from microphthalmia to anophthalmia. Zebrafish rx3 null mutants produce a similar striking eyeless phenotype with an associated expanded forebrain. Thus, we used zebrafish rx3-/- mutants as a model to uncover an Rx3-regulated gene network during early eye morphogenesis. Results: Rx3-regulated genes were identified using whole transcriptomic sequencing (RNA-seq) of rx3-/- mutants and morphologically wild-type siblings during optic vesicle morphogenesis. A gene co-expression network was then constructed for the Rx3-regulated genes, identifying gene cross-talk during early eye development. Genes highly connected in the network are hub genes, which tend to exhibit higher expression changes between rx3-/- mutants and normal phenotype siblings. Hub genes down-regulated in rx3-/- mutants encompass homeodomain transcription factors and mediators of retinoid-signaling, both associated with eye development and known human eye disorders. In contrast, genes up-regulated in rx3-/- mutants are centered on Wnt signaling pathways, associated with brain development and disorders. The temporal expression pattern of Rx3-regulated genes was further profiled during early development from maternal stage until visual function is fully mature. Rx3-regulated genes exhibited synchronized expression patterns, and a transition of gene expression during the early segmentation stage when Rx3 was highly expressed. Furthermore, most of these deregulated genes are enriched with multiple RAX-binding motif sequences on the gene promoter. Conclusions: Here, we assembled a comprehensive model of Rx3-regulated genes during early eye morphogenesis. Rx3 promotes optic vesicle morphogenesis and represses brain development through a highly correlated and modulated network, exhibiting repression of genes mediating Wnt signaling and concomitant enhanced expression of homeodomain transcription factors and retinoid-signaling genes.
      318Scopus© Citations 15
  • Publication
    Pharmacological Restoration of Visual Function in a Blind Zebrafish Mutant Following Histone Deacetylase Inhibitor (HDACi) Treatment
    Background: Controversially, histone deacetylase (HDAC) inhibitors are in clinical trial for the treatment of inherited retinal degenerations. Previous studies report that patients suffering from Retinitis Pigmentosa (RP) show improved visual field and acuity following treatment with the HDAC inhibitor valproic acid (VPA) (Clemson, Tzekov et al. 2011). However, other studies disagree with these findings (van Schooneveld, van den Born et al. 2011) and (Bhalla, Joshi et al. 2013). Thus, we sought to determine if treatment with HDACi rescued visual function and retinal morphology in a blind zebrafish dying-on-edge (dye) mutant identified from a forward genetics screen.
  • Publication
    Can histone deacetylase inhibitors uncover novel therapeutic agents for inherited retinal dystrophies
    Inherited retinal dystrophies (iRDs) affect 1 in 3000 people worldwide and effective treatment options are not widely available due to the genetic and clinical heterogeneity. Recently, histone deacetylase inhibitors (HDACi) have gained attention as a potential therapeutic option based on their neuroprotective effects within the retina. However, the benefits of HDACi remains highly controversial, and their downstream mechanism of action are yet to be thoroughly elucidated. Preliminary data from studies conducted has shown that treatment of zebrafish retinal mutant with HDACi, trichostatin A (TSA), could rescue visual capacity and retinal morphology. The current study is designed to address the suitability of HDACi as therapeutic options for iRDs using zebrafish models.
  • Publication
    Phenotype-Based Discovery of Novel Drugs for Ocular Disease
    (British Pharmacological Society, 2014)
    Our goal is to discover novel drugs with potential to improve the treatment of ocular disease.
  • Publication
    Structure-activity relationship of a novel family of cysteinyl leukotriene receptor antagonist quinoline compounds with anti-angiogenic activity
    Introduction: Previously, we identified quininib (2-[(E)-2-(quinolin-2-yl)vinyl]phenol), a cysteinyl leukotriene receptor antagonist with anti-angiogenic and anti-permeable activity (1,2). Here, we report a structure activity relationship study to more comprehensively characterise features which confer anti-angiogenic activity.
  • Publication
    Early safety assessment of human oculotoxic drugs using the zebrafish visualmotor response
    Introduction: Many prescribed drugs can adversely affect the eye by causing damage to the function of visual pathways or toxicity to the retina. Zebrafish have the potential to efficiently predict drugs with adverse ocular effects at pre-clinical stages of development. In this study, we explore the potential of using a semi-automated visual behaviour assay to predict drug-induced ocular toxicity in wild-type zebrafish larvae. Methods: 3 dpf larvae were treated with six known oculotoxic drugs and five control drugs in embryo medium containing 0.1% DMSO. After 48 h, larvae were assessed using the visualmotor response (VMR), an assay which quantifies locomotor responses to light changes; the optokinetic response (OKR), a behavioural assay that quantifies saccadic eye responses to rotating stimuli; and the touch response, a locomotor response to tactile stimuli. Results: 9 of 10 negative control drugs had no effect on zebrafish visual behaviour. 5 of the 6 known oculotoxic drugs (digoxin, gentamicin, ibuprofen, minoxidil and quinine) showed adverse effects on zebrafish visual behaviour assessed by OKR or the more automated VMR. No gross morphological changes were observed in treated larvae. The general locomotor activity of treated larvae, tested using the touch response assay, showed no differences with respect to controls. Overall the VMR assay had a sensitivity of 83%, a specificity of 100% and a positive predictive value of 100%. Discussion: This study confirms the suitability of the VMR assay as an efficient and predictive pre-clinical approach to evaluate adverse ocular effects of drugs on visual function in vivo.
      683Scopus© Citations 44
  • Publication
    Histone Deacetylase: Therapeutic Targets in Retinal Degeneration
    Previous studies report that retinitis pigmentosa (RP) patients treated with the histone deacetylase inhibitor (HDACi) valproic acid (VPA) present with improved visual fields and delayed vision loss. However, other studies report poor efficacy and safety of HDACi in other cohorts of retinal degeneration patients. Furthermore, the molecular mechanisms by which HDACi can improve visual function is unknown, albeit HDACi can attenuate pro-apoptotic stimuli and induce expression of neuroprotective factors. Thus, further analysis of HDACi is warranted in pre-clinical models of retinal degeneration including zebrafish. Analysis of HDAC expression in developing zebrafish reveals diverse temporal expression patterns during development and maturation of visual function.
      143Scopus© Citations 12
  • Publication
    GATD3A, a mitochondrial deglycase with evolutionary origins from gammaproteobacteria, restricts the formation of advanced glycation end products
    Background: Functional complexity of the eukaryotic mitochondrial proteome is augmented by independent gene acquisition from bacteria since its endosymbiotic origins. Mammalian homologs of many ancestral mitochondrial proteins have uncharacterized catalytic activities. Recent forward genetic approaches attributed functions to proteins in established metabolic pathways, thereby limiting the possibility of identifying novel biology relevant to human disease. We undertook a bottom-up biochemistry approach to discern evolutionarily conserved mitochondrial proteins with catalytic potential. Results: Here, we identify a Parkinson-associated DJ-1/PARK7-like protein—glutamine amidotransferase-like class 1 domain-containing 3A (GATD3A), with bacterial evolutionary affinities although not from alphaproteobacteria. We demonstrate that GATD3A localizes to the mitochondrial matrix and functions as a deglycase. Through its amidolysis domain, GATD3A removes non-enzymatic chemical modifications produced during the Maillard reaction between dicarbonyls and amines of nucleotides and amino acids. GATD3A interacts with factors involved in mitochondrial mRNA processing and translation, suggestive of a role in maintaining integrity of important biomolecules through its deglycase activity. The loss of GATD3A in mice is associated with accumulation of advanced glycation end products (AGEs) and altered mitochondrial dynamics. Conclusions: An evolutionary perspective helped us prioritize a previously uncharacterized but predicted mitochondrial protein GATD3A, which mediates the removal of early glycation intermediates. GATD3A restricts the formation of AGEs in mitochondria and is a relevant target for diseases where AGE deposition is a pathological hallmark.
      16Scopus© Citations 1
  • Publication
    Genetic Deletion of Zebrafish Rab28 Causes Defective Outer Segment Shedding, but Not Retinal Degeneration
    The photoreceptor outer segment is the canonical example of a modified and highly specialized cilium, with an expanded membrane surface area in the form of disks or lamellae for efficient light detection. Many ciliary proteins are essential for normal photoreceptor function and cilium dysfunction often results in retinal degeneration leading to impaired vision. Herein, we investigate the function and localization of the ciliary G-protein RAB28 in zebrafish cone photoreceptors. CRISPR-Cas9 generated rab28 mutant zebrafish display significantly reduced shed outer segment material/phagosomes in the RPE at 1 month post fertilization (mpf), but otherwise normal visual function up to 21 dpf and retinal structure up to 12 mpf. Cone photoreceptor-specific transgenic reporter lines show Rab28 localizes almost exclusively to outer segments, independently of GTP/GDP nucleotide binding. Co-immunoprecipitation analysis demonstrates tagged Rab28 interacts with components of the phototransduction cascade, including opsins, phosphodiesterase 6C and guanylate cyclase 2D. Our data shed light on RAB28 function in cones and provide a model for RAB28-associated cone-rod dystrophy.
      121Scopus© Citations 5