Multiphoton imaging of chick retinal development in relation to gap junctional communication

Ethanol Causes Cell Death and Neuronal Differentiation Defect During Initial Neurogenesis of the Neural Retina by Disrupting Calcium Signaling in Human Retinal Organoids

Fetal Alcohol Syndrome (FAS) affects a significant proportion, exceeding 90%, of afflicted children, leading to severe ocular aberrations such as microphthalmia and optic nerve hypoplasia. During the early stages of pregnancy, the commencement of neural retina neurogenesis represents a critical period for human eye development, concurrently exposing the developing retinal structures to the highest risk of prenatal ethanol exposure due to a lack of awareness. Despite the paramount importance of this period, the precise influence and underlying mechanisms of short-term ethanol exposure on the developmental process of the human neural retina have remained largely elusive. In this study, we utilize the human embryonic stem cells derived retinal organoids (hROs) to recapitulate the initial retinal neurogenesis and find that 1% (v/v) ethanol slows the growth of hROs by inducing robust cell death and retinal ganglion cell differentiation defect. Bulk RNA-seq analysis and two-photon microscope live calcium imaging reveal altered calcium signaling dynamics derived from ethanol-induced down-regulation of RYR1 and CACNA1S. Moreover, the calcium-binding protein RET, one of the downstream effector genes of the calcium signaling pathway, synergistically integrates ethanol and calcium signals to abort neuron differentiation and cause cell death. To sum up, our study illustrates the effect and molecular mechanism of ethanol on the initial neurogenesis of the human embryonic neural retina, providing a novel interpretation of the ocular phenotype of FAS and potentially informing preventative measures for susceptible populations.

Culture of Adult Transgenic Zebrafish Retinal Explants for Live-cell Imaging by Multiphoton Microscopy

An endogenous regeneration program is initiated by Müller glia in the adult zebrafish (Danio rerio) retina following neuronal damage and death. The Müller glia re-enter the cell cycle and produce neuronal progenitor cells that undergo subsequent rounds of cell divisions and differentiate into the lost neuronal cell types. Both Müller glia and neuronal progenitor cell nuclei replicate their DNA and undergo mitosis in distinct locations of the retina, i.e. they migrate between the basal Inner Nuclear Layer (INL) and the Outer Nuclear Layer (ONL), respectively, in a process described as Interkinetic Nuclear Migration (INM). INM has predominantly been studied in the developing retina. To examine the dynamics of INM in the adult regenerating zebrafish retina in detail, live-cell imaging of fluorescently-labeled Müller glia/neuronal progenitor cells is required. Here, we provide the conditions to isolate and culture dorsal retinas from Tg[gfap:nGFP]^mi2004 zebrafish that were exposed to constant intense light for 35 h. We also show that these retinal cultures are viable to perform live-cell imaging experiments, continuously acquiring z-stack images throughout the thickness of the retinal explant for up to 8 h using multiphoton microscopy to monitor the migratory behavior of gfap:nGFP-positive cells. In addition, we describe the details to perform post-imaging analysis to determine the velocity of apical and basal INM. To summarize, we established conditions to study the dynamics of INM in an adult model of neuronal regeneration. This will advance our understanding of this crucial cellular process and allow us to determine the mechanisms that control INM.

Dendritic changes in rat visual pathway associated with experimental ocular hypertension

PURPOSE

Increasing evidence shows that structural changes in dendrites play an important role in neuronal degenerative processes. The aims of this study were to characterize and delineate morphological changes of dendrites in retinal ganglion cells (RGCs) and their central target neurons in the superior colliculus (SC) and lateral geniculate nucleus (LGN) in experimental rat glaucoma.

METHODS

Chronic ocular hypertension (OHT) was surgically induced in rats and animals were sacrificed at 1, 4, 8, 16 and 32 weeks following IOP elevation. Animals without IOP elevation served as normal control. Dendritic morphology of neurons was visualized by ex vivo DiI labelling using confocal microscopy and dendritic length and number was quantified using Image J.

RESULTS

We found significant dendritic shrinkage (p < 0.001) and loss (p < 0.001) in RGCs and neurons in the SC and LGN in OHT animals compared to age-matched controls. Analysis of the temporal morphological profiles among them revealed the RGCs to have the earliest changes compared to the SC and LGN although the most prominent changes occurred in the SC.

CONCLUSION

Our study has demonstrated that OHT results in dendritic changes of the neurons throughout the visual pathways, from RGCs to SC cells and LGN cells, suggesting that both the retina and the brain should be targeted when considering diagnosis and therapeutic strategies for glaucoma.

Interkinetic nuclear migration: beyond a hallmark of neurogenesis

Interkinetic nuclear migration (INM) is an oscillatory nuclear movement that is synchronized with the progression of the cell cycle. The efforts of several researchers, following the first report of INM in 1935, have revealed many of the molecular mechanisms of this fascinating phenomenon linking the timing of the cell cycle and nuclear positioning in tissue. Researchers are now faced with a more fundamental question: is INM important for tissue, particularly brain, development? In this review, I summarize the current understanding of the regulatory mechanisms governing INM, investigations involving several different tissues and species, and possible explanations for how nuclear movement affects cell-fate determination and tissue formation.

Cytoskeleton proteins previously considered exclusive to ganglion cells are transiently expressed by all retinal neuronal precursors

Background

Understanding the mechanisms governing cell fate specification remains one of the main challenges in the study of retinal development. In this context, molecular markers that identify specific cell types become crucial tools for the analysis and interpretation of these phenomena. In studies using the developing chick retina, expression of the mid-size neurofilament (NF-M) and a chick-specific microtubule associated protein recognized by the RA4 antibody (MAP(RA4)), have been broadly used to selectively identify ganglion cells and their committed precursors. However, observations in our laboratory suggested that the expression of these proteins may not be restricted to cells of the ganglion cell lineage. Because of its potential significance in the field, we pursued a detailed analysis of the expression of these two molecules in combination with an array of proteins that allowed precise identification of all retinal cell-type precursors throughout the development of the chick retina.

Results

Both, NF-M and MAP(RA4) proteins, showed a dynamic pattern of expression coincident with the progression of retinal cell differentiation. Both proteins were coexpressed spatially and temporally in postmitotic neuronal precursors throughout development. Expression of both proteins was seen in ganglion cell precursors and adult differentiated ganglion cells, but they were also transiently expressed by precursors of the photoreceptor, horizontal, bipolar and amacrine cell lineages.

Conclusions

We have clearly demonstrated that, contrary to the generally accepted paradigm, expression of NF-M and MAP(RA4) proteins is not exclusive to ganglion cells. Rather, both proteins are transiently expressed by all neuronal retinal progenitors in a developmentally-regulated manner. In addition, MAP(RA4) and NF-M are the first molecules so far characterized that may allow unambiguous identification of postmitotic precursors from the pool of mitotically active progenitors and/or the differentiated cell population during retinogenesis. These results are of significant impact for the field of developmental biology of the retina, since they provide novel and important information for the appropriate design and interpretation of studies on retinal cell differentiation, as well as for the reinterpretation of previously published studies.

Gap-Junction Proteins in Retinal Development: New Roles for the “Nexus”

Gap-junction channels, the cytoplasmic proteins that associate with them, and the transcriptional networks that regulate them are increasingly being viewed as critical communications hubs for cell signaling in health and disease. As a result, the term “nexus,” which was the original structural name for these focal intercellular links, is coming back into use with new proteomic and transcriptomic meanings. The retina is better understood than any other part of the vertebrate central nervous system in respect of its developmental patterning, its diverse neuronal types and circuits, and the emergence of its definitive structure-function correlations. Thus, studies of the junctional and nonjunctional nexus roles of gap-junction proteins in coordinating retinal development should throw useful light on cell signaling in other developing nervous tissues.