Clinical and genetic heterogeneity associated with retinal diseases makes stem-cell-based therapies an attractive strategy for personalized medicine. However, we have limited understanding of the timing of key events in the developing human retina, and in particular the factors critical for generating the unique architecture of the fovea and surrounding macula. Here we define three key epochs in the transcriptome dynamics of human retina from fetal day (D) 52 to 136. Coincident histological analyses confirmed the cellular basis of transcriptional changes and highlighted the dramatic acceleration of development in the fovea compared with peripheral retina. Human and mouse retinal transcriptomes show remarkable similarity in developmental stages, although morphogenesis was greatly expanded in humans. Integration of DNA accessibility data allowed us to reconstruct transcriptional networks controlling photoreceptor differentiation. Our studies provide insights into human retinal development and serve as a resource for molecular staging of human stem-cell-derived retinal organoids.

The striatum regulates motor control, reward, and learning. Abnormal function of striatal GABAergic medium spiny neurons (MSNs) is believed to contribute to the deficits in these processes that are observed in many neuropsychiatric diseases. The orphan G-protein-coupled receptor (GPCR) GPR88 is robustly expressed in MSNs and regulated by neuropharmacological drugs, but its contribution to MSN physiology and behavior is unclear. Here we show that in the absence of GPR88, MSNs have increased glutamatergic excitation and reduced GABAergic inhibition that together promote enhanced firing rates in vivo, resulting in hyperactivity, poor motor-coordination, and impaired cue-based learning in mice. Targeted viral expression of GPR88 in MSNs rescues the molecular and electrophysiological properties and normalizes behavior, suggesting that aberrant MSN activation in the absence of GPR88 underlies behavioral deficits and its dysfunction may contribute to behaviors observed in neuropsychiatric disease.

Most regions of the vertebrate central nervous system develop by the sequential addition of different classes of neurons and glia. This phenomenon has been best characterized in laminated structures like the retina and the cerebral cortex, in which the progenitor cells in these structures are thought to change in their competence as development proceeds to generate different types of neurons in a stereotypic sequence that is conserved across vertebrates. We previously reported that conditional deletion of Dicer prevents the change in competence of progenitors to generate later-born cell types, suggesting that specific microRNAs (miRNAs) are required for this developmental transition. In this report, we now show that three miRNAs, let-7, miR-125, and miR-9, are key regulators of the early to late developmental transition in retinal progenitors: (i) members of these three miRNA families increase over the relevant developmental period in normal retinal progenitors; (ii) inhibiting the function of these miRNAs produces changes in retinal development similar to Dicer CKO; (iii) overexpression of members of these three miRNA families in Dicer-CKO retinas can rescue the phenotype, allowing their progression to late progenitors; (iv) overexpression of these miRNAs can accelerate normal retinal development; (v) microarray and computational analyses of Dicer-CKO retinal cells identified two potential targets of the late-progenitor miRNAs: Protogenin (Prtg) and Lin28b; and (vi) overexpression of either Lin28 or Prtg can maintain the early progenitor state. Together, these data demonstrate that a conserved miRNA pathway controls a key step in the progression of temporal identity in retinal progenitors.heterochronic | progenitor competence

BackgroundThe brain, spinal cord, and neural retina comprise the central nervous system (CNS) of vertebrates. Understanding the regulatory mechanisms that underlie the enormous cell-type diversity of the CNS is a significant challenge. Whole-genome mapping of DNase I-hypersensitive sites (DHSs) has been used to identify cis-regulatory elements in many tissues. We have applied this approach to the mouse CNS, including developing and mature neural retina, whole brain, and two well-characterized brain regions, the cerebellum and the cerebral cortex.ResultsFor the various regions and developmental stages of the CNS that we analyzed, there were approximately the same number of DHSs; however, there were many DHSs unique to each CNS region and developmental stage. Many of the DHSs are likely to mark enhancers that are specific to the specific CNS region and developmental stage. We validated the DNase I mapping approach for identification of CNS enhancers using the existing VISTA Browser database and with in vivo and in vitro electroporation of the retina. Analysis of transcription factor consensus sites within the DHSs shows distinct region-specific profiles of transcriptional regulators particular to each region. Clustering developmentally dynamic DHSs in the retina revealed enrichment of developmental stage-specific transcriptional regulators. Additionally, we found reporter gene activity in the retina driven from several previously uncharacterized regulatory elements surrounding the neurodevelopmental gene Otx2. Identification of DHSs shared between mouse and human showed region-specific differences in the evolution of cis-regulatory elements.ConclusionsOverall, our results demonstrate the potential of genome-wide DNase I mapping to cis-regulatory questions regarding the regional diversity within the CNS. These data represent an extensive catalogue of potential cis-regulatory elements within the CNS that display region and temporal specificity, as well as a set of DHSs common to CNS tissues. Further examination of evolutionary conservation of DHSs between CNS regions and different species may reveal important cis-regulatory elements in the evolution of the mammalian CNS.Electronic supplementary materialThe online version of this article (doi:10.1186/1756-8935-8-8) contains supplementary material, which is available to authorized users.

Across neurodegenerative diseases, common mechanisms may reveal novel therapeutic targets based on neuronal protection, repair, or regeneration, independent of etiology or site of disease pathology. To address these mechanisms and discuss emerging treatments, in April, 2021, Glaucoma Research Foundation, BrightFocus Foundation, and the Melza M. and Frank Theodore Barr Foundation collaborated to bring together key opinion leaders and experts in the field of neurodegenerative disease for a virtual meeting titled “Solving Neurodegeneration”. This “think-tank” style meeting focused on uncovering common mechanistic roots of neurodegenerative disease and promising targets for new treatments, catalyzed by the goal of finding new treatments for glaucoma, the world’s leading cause of irreversible blindness and the common interest of the three hosting foundations. Glaucoma, which causes vision loss through degeneration of the optic nerve, likely shares early cellular and molecular events with other neurodegenerative diseases of the central nervous system. Here we discuss major areas of mechanistic overlap between neurodegenerative diseases of the central nervous system: neuroinflammation, bioenergetics and metabolism, genetic contributions, and neurovascular interactions. We summarize important discussion points with emphasis on the research areas that are most innovative and promising in the treatment of neurodegeneration yet require further development. The research that is highlighted provides unique opportunities for collaboration that will lead to efforts in preventing neurodegeneration and ultimately vision loss.

The signaling cascades governing neuronal migration are believed to link extracellular signals to cytoskeletal components. MAP1B is a neuron-specific microtubule-associated protein implicated in the control of the dynamic stability of microtubules and in the cross-talk between microtubules and actin filaments. Here we show that Reelin can induce mode I MAP1B phosphorylation, both in vivo and in vitro, through gsk3 and cdk5 activation. Additionally, mDab1 participates in the signaling cascade responsible for mode I MAP1B phosphorylation. Conversely, MAP1B-deficient mice display an abnormal structuring of the nervous system, especially in brain laminated areas, indicating a failure in neuronal migration. Therefore, we propose that Reelin can induce post-translational modifications on MAP1B that could correlate with its function in neuronal migration.

Epigenetic regulation, including histone modification, is a critical component of gene regulation, although precisely how this contributes to the development of complex tissues such as the neural retina is still being explored. We show that during retinal development in mouse, there are dynamic patterns of expression of the polycomb repressive complex 2 (PRC2) catalytic subunit EZH2 in retinal progenitors and some differentiated cells, as well as dynamic changes in the histone modification H3K27me3. Using conditional knockout of Ezh2 using either Pax6-αCre or Six3-Cre, we find selective reduction in postnatal retinal progenitor proliferation, disruption of retinal lamination, and enhanced differentiation of several late born cell types in the early postnatal retina, including photoreceptors and Müller glia, which are ultimately increased in number and become reactive. RNA-seq identifies many non-retinal genes upregulated with loss of Ezh2, including multiple Hox genes and the cell cycle regulator Cdkn2a, which are established targets of EZH2-mediated repression. ChIP analysis confirms loss of the H3K27me3 modification at these loci. Similar gene upregulation is observed in retinal explants treated with an EZH2 chemical inhibitor. There is considerable overlap with EZH2-regulated genes reported in non-neural tissues, suggesting that EZH2 can regulate similar genes in multiple lineages. Our findings reveal a conserved role for EZH2 in constraining the expression of potent developmental regulators to maintain lineage integrity and retinal progenitor proliferation, as well as regulating the timing of late differentiation.

These data indicate that MAP1B phosphorylation is controlled by Netrin 1 and that the lack of MAP1B impairs Netrin 1-mediated chemoattraction in vitro and in vivo. Thus, MAP1B may be a downstream effector in the Netrin 1-signaling pathway.