Neural differentiation and synaptogenesis in retinal development

To investigate the pattern of neural differentiation and synaptogenesis in the mouse retina, immunolabeling, Brd U assay and transmission electron microscopy were used. We show that the neuroblastic cell layer is the germinal zone for neural differentiation and retinal lamination. Ganglion cells differentiated initially at embryonic day 13（E13）, and at E18 horizontal cells appeared in the neuroblastic cell layer. Neural stem cells in the outer neuroblastic cell layer differentiated into photoreceptor cells as early as postnatal day 0（P0）, and neural stem cells in the inner neuroblastic cell layer differentiated into bipolar cells at P7. Synapses in the retina were mainly located in the outer and inner plexiform layers. At P7, synaptophysin immunostaining appeared in presynaptic terminals in the outer and inner plexiform layers with button-like structures. After P14, presynaptic buttons were concentrated in outer and inner plexiform layers with strong staining. These data indicate that neural differentiation and synaptogenesis in the retina play important roles in the formation of retinal neural circuitry. Our study showed that the period before P14, especially between P0 and P14, represents a critical period during retinal development. Mouse eye opening occurs during that period, suggesting that cell differentiation and synaptic formation lead to the attainment of visual function.

Onecut transcription factors in retinal development and maintenance

The retina and its development： The retina is an essential part of the visual system. A myriad of eye diseases are characterized by retinal degeneration, caused by either genetic or environmental factors. This underscores the importance of studying the genetic and molecular mechanisms that regulate the generation and maintenance of neurons in the mammalian retina. Our recent studies demonstrate that two related transcription factors Onecutl （Ocl） and Onecut2 （0c2） regulate multiple cell fates in the mouse retina, and their absence results in progressive retinal neurodegeneration （Wu et al., 2012, 2013; Sapkota et al., 2014）.

Comment on concurrent removal of intravitreal lens fragments after phacoemulsification with pars plana vitrectomy prevents development of retinal detachment

I read with interest the article entitled ＂Concurrent removal of intravitreal lens fragments afterphacoemulsification with pars plana vitrectomy prevents development of retinal detachment＂ by Chalam et al . In this study, none of the patients developed retinal detachment （RD） during the one-year follow-up after concurrent removal lens fragments following phacoemulsification with pars plana vitrectomy （PPV）. The authors suggested that concurrent PPV for retained lens fragments after cataract surgery might prevent development of rhegmatogenous retinal detachment （RRD）, because early PPV prevents development of intraocular inflammation and inhibits vitreous contraction, a common cause of retinal tears and detachment.

Retinal regeneration requires dynamic Notch signaling

Retinal damage in the adult zebrafish induces Müller glia reprogramming to produce neuronal progenitor cells that proliferate and differentiate into retinal neurons.Notch signaling,which is a fundamental mechanism known to drive cell-cell communication,is required to maintain Müller glia in a quiescent state in the undamaged retina,and repression of Notch signaling is necessary for Müller glia to reenter the cell cycle.The dynamic regulation of Notch signaling following retinal damage also directs proliferation and neurogenesis of the Müller glia-derived progenitor cells in a robust regeneration response.In contrast,mammalian Müller glia respond to retinal damage by entering a prolonged gliotic state that leads to additional neuronal death and permanent vision loss.Understanding the dynamic regulation of Notch signaling in the zebrafish retina may aid efforts to stimulate Müller glia reprogramming for regeneration of the diseased human retina.Recent findings identified DeltaB and Notch3 as the ligand-receptor pair that serves as the principal regulators of zebrafish Müller glia quiescence.In addition,multi-omics datasets and functional studies indicate that additional Notch receptors,ligands,and target genes regulate cell proliferation and neurogenesis during the regeneration time course.Still,our understanding of Notch signaling during retinal regeneration is limited.To fully appreciate the complex regulation of Notch signaling that is required for successful retinal regeneration,investigation of additional aspects of the pathway,such as post-translational modification of the receptors,ligand endocytosis,and interactions with other fundamental pathways is needed.Here we review various modes of Notch signaling regulation in the context of the vertebrate retina to put recent research in perspective and to identify open areas of inquiry.

Possible role of sialylation of retinal protein glycans in the regulation of electroretinogram response in mice

AIM： To evaluate if the nature, degree and extent of Siaa2-3-/Siaa2-6-sialylation of retinal protein glycans plays a possible role in the development and regulation of electroretinogram response （ERG） in mice. METHODS： Proteins extracted, from retinae of postnatal day 2 （PN2）, PN7, and PN14 wild type （wt） and retinal degeneration 1 （rdl） mice were quantified, labeled and used for lectin-microarray profiling with immobilized lectins which recognize a wide range of N-/O-glycans. Net fluorescence intensities of lectin-ligand complexes were measured and images of fluorescent lectin-microarrays were acquired. From the binding curves between each lectin and protein extracts from PN14 wt and PN14 rdl mice retinae, the protein concentration was selected to determine optimum signal intensity for lectin-ligand binding. Mean_＋SEM values of proteins and fluorescence- intensities of lectin-ligand-complexes between 45 lectins and 36 protein extracts from wt and rdl mice retinae were compared for significance of differences. RESULTS： Comparison of the progressive relative changes in the sialylated glycans of retinal proteins from wt and rdl mice showed that Siao2-3Gall-4GIcNAc-glycans （but not Siaa2-6-glycans） were detectable and quantifiable from the retinal-proteins of PN7 and PN14 wt and rdl mice. Siaa2- 3-sialylation of retinal-protein Gal/o-linked-Gal-glycans was significantly increased with age in PN7 and PN14 wt and less so in PN14 rdl mice. Siao2-3-/Siaa2-6-sialylation of retinal-protein Gal/a-linked-Gal-glycans was absent in PN2 wt and rdl mice. Comparison of published ERG responses of wt and rdl mice retinae with degree of Siaa2- 3-sialylation of retinal-protein-glycans showed that PN2 wt and rdl mice lack both the ERG response and Siaa2- 3-/Siao2-6-sialylation of retinal-protein Gal/a-linked-Gal-glycans; rdl mice with relatively lower Siaa2-3-sialylation of retinal-protein Gal/a-linked-Gal-glycans showed aberrant ERG response; and wt mice with significantly higher Siaa2-3-sialylation of retinal-protein Gal/a-linked- Gal-glycans showed normal ERG response. CONCLUSION： Degree of Siaa2-3-sialylation of giycans possibly regulates ERG function in mice.

Expression profiles of long noncoding RNAs in retinopathy of prematurity

Long noncoding RNA(lncRNA)regulates the proliferation and migration of human retinal endothelial cells,as well as retinal neovascularization in diabetic retinopathy.Based on similarities between the pathogenesis of retinopathy of prematurity(ROP)and diabetic retinopathy,lncRNA may also play a role in ROP.Seven-day-old mice were administered 75±2% oxygen for 5 days and normoxic air for another 5 days to establish a ROP model.Expression of lncRNA and mRNA in the retinal tissue of mice was detected by high-throughput sequencing technology,and biological functions of the resulted differentially expressed RNAs were evaluated by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses.The results showed that compared with the control group,57 lncRNAs were differentially expressed,including 43 upregulated and 14 downregulated,in the retinal tissue of ROP mice.Compared with control mice,42 mRNAs were differentially expressed in the retinal tissue of ROP mice,including 24 upregulated and 18 downregulated mRNAs.Differentially expressed genes were involved in ocular development and related metabolic pathways.The differentially expressed lncRNAs may regulate ROP in mice via microRNAs and multiple signaling pathways.Our results revealed that these differentially expressed lncRNAs may be therapeutic targets for ROP treatment.This study was approved by the Medical Ethics Committee of Shengjing Hospital of China Medical University on February 25,2016(approval No.2016PS074K).