Functional Role of the RNA-Binding Protein Rbm24a and Its Target sox2 in Microphthalmia

Overexpression of Bmp4 induces microphthalmia by disrupting embryonic neural retina

Microphthalmia, mostly an autosomal dominant disorder, is a worldwide severe congenital ocular malformation that causes visual impairment. Our investigation unveiled a total of 30 genes associated with microphthalmia. Employing the CytoHubba and PPI network, we identified Bmp4 as the most pivotal hub gene. Subsequently, the conditional overexpression of Bmp4 in the retina caused highly distinctive microphthalmia, manifested by retinal disorganization with ganglion cell misalignment. Significant reduction in the number and abnormal distribution location of retinal cells in microphthalmia model mice. Elevated Bmp4 was associated with an increase in retinal apoptosis and a decrease in proliferating cells, which exacerbates the development of microphthalmia. Here we identify Bmp4 as an extremely important gene responsible for microphthalmia and the involved mechanisms. Overexpression of Bmp4 induces retinal cell ectopic expression and developmental defects, highlighting the importance of a well-balanced Bmp4 level in shaping the embryonic retina during early development.

Abnormal eyes and spine development in zebrafish (Danio rerio) embryos and larvae induced by triphenyltin

Triphenyltin (TPT) is widely used in crop pest control and ship antifouling coatings, which leads to its entry into aquatic environment and poses a threat to aquatic organisms. However, the effects of TPT on the early life stages of wild fish in natural water environments remains unclear. The aim of this study was to assess the toxic effects of TPT on the early life stages of fish under two different environments: field investigation and laboratory experiment. The occurrence of deformities in wild fish embryos and larvae in the Three Gorges Reservoir (TGR) and the developmental toxicity of TPT at different concentrations (0, 0.15, 1.5 and 15 μg Sn/L) to zebrafish embryos and larvae were observed. The results showed that TPT content was higher in wild larvae, reaching 27.21 ng Sn/g w, and the malformation of wild fish larvae mainly occurred in the eyes and spine under natural water environment. Controlled experiment exposure of zebrafish larvae to TPT also resulted in eye and spinal deformities. Gene expression analysis showed that compared with the control group, the expression levels of genes related to eye development (sox2, otx2, stra6 and rx1) and spine development (sox9a and bmp2b) were significantly up-regulated in the 15 μg Sn/L exposure group, which may be the main cause of eye and spine deformity in the early development stage of fish. In addition, the molecular docking results further elucidate that the strong hydrophobic and electrostatic interactions between TPT and protein residues are the main mechanism of TPT induced abnormal gene expression. Based on these results, it can be inferred that TPT is one of the teratogenic factors of abnormal eye and spine development in the early life stage of fish in the TGR. These findings have important implications for understanding the toxicity of TPT on fish.

Effects of acute exposure to amisulbrom on retinal development in zebrafish (Danio rerio) embryos

Amisulbrom is an oomycete-specific fungicide that was developed by Nissan Chemical Industries Limited. The exposure of developing zebrafish embryo to amisulbrom caused disorders in the visual phototransduction system. However, the potential toxic mechanisms of amisulbrom on retinal development remains unclear. The research purpose of this study was to evaluate the adverse effects of amisulbrom on retinal development in a model organism, the zebrafish. Zebrafish embryos were treated with 0, 0.0075, 0.075, or 0.75 μM amisulbrom from 3 h post-fertilization (hpf) to 72 hpf. Compared with the control group, amisulbrom-treated zebrafish embryos displayed phenotypic microphthalmia, dysregulation of gene transcription levels (alcama, prox1a, sox2, vsx1, rho, bluops, rdops, uvops, and grops) related to the retinal cell layer differentiation, and increased retinal apoptosis. In addition, the content of glutathione and malondialdehyde increased significantly after exposure to amisulbrom. Overall, our data demonstrate the toxicity of amisulbrom to eye development, which will help to assess the potential ecotoxicological impacts posed by amisulbrom to aquatic species.

RNA-binding proteins and post-transcriptional regulation in lens biology and cataract: Mediating spatiotemporal expression of key factors that control the cell cycle, transcription, cytoskeleton and transparency

Development of the ocular lens - a transparent tissue capable of sustaining frequent shape changes for optimal focusing power - pushes the boundaries of what cells can achieve using the molecular toolkit encoded by their genomes. The mammalian lens contains broadly two types of cells, the anteriorly located monolayer of epithelial cells which, at the equatorial region of the lens, initiate differentiation into fiber cells that contribute to the bulk of the tissue. This differentiation program involves massive upregulation of select fiber cell-expressed RNAs and their subsequent translation into high amounts of proteins, such as crystallins. But intriguingly, fiber cells achieve this while also simultaneously undergoing significant morphological changes such as elongation - involving about 1000-fold length-wise increase - and migration, which requires modulation of cytoskeletal and cell adhesion factors. Adding further to the challenges, these molecular and cellular events have to be coordinated as fiber cells progress toward loss of their nuclei and organelles, which irreversibly compromises their potential for harnessing genetically hardwired information. A long-standing question is how processes downstream of signaling and transcription, which may also participate in feedback regulation, contribute toward orchestrating these cellular differentiation events in the lens. It is now becoming clear from findings over the past decade that post-transcriptional gene expression regulatory mechanisms are critical in controlling cellular proteomes and coordinating key processes in lens development and fiber cell differentiation. Indeed, RNA-binding proteins (RBPs) such as Caprin2, Celf1, Rbm24 and Tdrd7 have now been described in mediating post-transcriptional control over key factors (e.g. Actn2, Cdkn1a (p21Cip1), Cdkn1b (p27Kip1), various crystallins, Dnase2b, Hspb1, Pax6, Prox1, Sox2) that are variously involved in cell cycle, transcription, cytoskeleton maintenance and differentiation in the lens. Furthermore, deficiencies of these RBPs have been shown to result in various eye and lens defects and/or cataract. Because fiber cell differentiation in the lens occurs throughout life, the underlying regulatory mechanisms operational in development are expected to also be recruited for the maintenance of transparency in aged lenses. Indeed, in support of this, TDRD7 and CAPRIN2 loci have been linked to age-related cataract in humans. Here, I will review the role of key RBPs in the lens and their importance in understanding the pathology of lens defects. I will discuss advances in RBP-based gene expression control, in general, and the important challenges that need to be addressed in the lens to define the mechanisms that determine the epithelial and fiber cell proteome. Finally, I will also discuss in detail several key future directions including the application of bioinformatics approaches such as iSyTE to study RBP-based post-transcriptional gene expression control in the aging lens and in the context of age-related cataract.