Strip1 regulates retinal ganglion cell survival by suppressing Jun-mediated apoptosis to promote retinal neural circuit formation
For journal club, we read a paper from Dr. Mai Ahmed who recently published her PhD work in eLife, titled “Strip1 regulates retinal ganglion cell survival by suppressing Jun-mediated apoptosis to promote retinal neural circuit formation”. This research came from Dr. Ichiro Masai’s lab at the Okinawa Institute of Science and Technology Graduate University (OIST).
Dr. Ahmed et al. sought to investigate how the complex organization of the retina properly develops by utilizing diverse approaches with zebrafish including mutagenesis screening, morpholino knockdowns, confocal imaging, transplantation, RNA-seq, and more. She found that in strip1 mutants, the inner plexiform layer (IPL) is severely disrupted due to cell death of retinal ganglion cells (RGCs). With this loss, cells from other layers (including amacrine and bipolar cells) improperly enter the RGC layer and disrupt the IPL. So how does strip1 normally ensure RGC survival? Dr. Ahmed first showed that strip1 acts cell autonomously on RGCs along with an interacting partner strn3: together, these proteins suppress the action of the proapoptotic protein Jun in RGCs. Yet when RGC survival is rescued by Bcl2 overexpression in strip1 mutants, an ectopic IPL-like forms with little RGC innervation, revealing an additional patterning function of strip1 in RGCs.
Dr. Ahmed has shared a wonderful story of retinal development that is well-worth the read. We look forward to seeing more of her work as a Junior Research Fellow at OIST.
Last month in journal club we read Dr. Daniela Roellig’s paper “Force-generating apoptotic cells orchestrate avian neural tube bending” from Dr. Magali Suzanne’s lab. Recently published in Developmental Cell, this was a new and exciting paper for the field of developmental biology and tissue remodeling. The authors examined the role of apoptosis in the process of neural tube folding in avian embryos. After observing a high density of apoptotic cells in dorsolateral hinge points of the folding neural tube, the authors asked how these dying cells might contribute to bending of the neuroepithelium. They discovered that as an apoptotic cell dies an apico-basal force is generated via actomyosin dynamics that causes deformations to both the apical and basal side of the neuroepithelium, which contributes to the physical bending. These findings advance our understanding of the mechanics of neural tube closure and highlight apoptosis as a key player in biomechanical processes.
“Identification of astroglia-like cardiac nexus glia that are critical regulators of cardiac development and function”
For this month’s journal club, Heather presented a paper by Dr. Nina Kikel-Coury and @cssmity entitled “Identification of astroglia-like cardiac nexus glia that are critical regulators of cardiac development and function.” This study described a new glial cell type in the zebrafish heart that appears to be conserved across species. These glia, dubbed cardiac nexus glia (CNGs), share multiple markers with astroglia, associate with synapses, and regulate axon infiltration into the heart, thus revealing similarities to CNS astroglia. CNGs appear to be derived from neural crest cells and differentiate through Meteorin-Jak/Stat3 signaling. The authors also showed that CNGs contribute to heart rate and rhythm modulation through both the sympathetic and parasympathetic systems. This study advances our knowledge of PNS glia and their contributions to physiology.
"Estrogens regulate early embryonic development of the olfactory sensory system via estrogen-responsive glia"
This week in journal club we discussed a recent article by Dr Aya Takesono and colleagues of the Tyler and Kudoh labs at @UniofExeter. https://t.co/6W9Rofmw1P.
Using an estrogen biosensor zebrafish line, the authors identified a novel type of glia, that they named estrogen-responsive olfactory bulb (EROB) cells.
The study shows that estrogens regulate EROB cell projections intricately interacting with olfactory sensory neurons and promote inhibitory synaptogenesis in the olfactory bulb. Conversely, EROB cell ablation/blocking estrogen signaling impairs the development of olfactory glomeruli.
Lastly, by using calcium sensors, this works demonstrates that estrogens establish the responsiveness of the embryonic olfactory system through EROB glia. Figure 1G illustrates EROB glia in the olfactory bulb of a tg(ERE:GFP) zebrafish larva.
"Satellite glia are essential modulators of sympathetic neuron survival, activity, and autonomic function"
In our October Journal Club we discussed a paper recently published on bioRxiv from Rejji Kuruvilla’s lab. First author Aurelia A. Mapps and co-workers investigated the contribution of satellite glia, which envelop neuronal cell bodies, to sympathetic functions. They found that satellite glial ablation resulted in soma atrophy of sympathetic neurons and neuronal loss, which was at least in part mediated via extracellular buffering of K+ via potassium channel Kir4.1 We were especially fascinated by the opposite effect satellite glia ablation had on the remaining neurons, which displayed an increase in activity, and mice with satellite glia had larger pupils and an elevated heart rate. This is an exciting study revealing that neuron-satellite communication is essential for sympathetic function!
In this month's journal club we discussed a paper from Vatsala Thirumalai's lab (https://doi.org/10.1523/ENEURO.0493-20.2021). The paper was chosen by Kendra, who is interested in the zebrafish touch response circuit. Co-first authors Urvashi Jha and Igor Kondrychyn investigated the role of auts2a in zebrafish Mauthner cells and how it affects escape behavior. Using imaging, behavior paradigms, and electrophysiology, they show that auts2a mutants display highly variable success in their escape response, stemming from a higher threshold in Mauthner cells. We were particularly intrigued by the auts2a mutant data, where the variability seems to arise from two groups: those similar to wild types and those with highly delayed escape responses. What causes the differences between these groups? It would be interesting to tease apart the differences between the mutant phenotypes!
"Zebrafish Cdx4 regulates neural crest cell specification and migratory behaviors in the posterior body"
For our September journal club, we read the recently published paper by Dr. Manuel Rocha from his PhD work in the Prince lab, “Zebrafish Cdx4 regulates neural crest cell specification and migratory behaviors in the posterior body”. This paper includes beautiful images from our favorite model organism and introduces a new gene, cdx4, involved in neural crest (NC) cell specification and segmental migration in the zebrafish trunk. The analyses include an array of techniques from in situ hybridization chain reaction, to single-plane illumination microscopy and some complex bioinformatics! Together, their studies demonstrate that cdx4 not only establishes migratory behaviors of NC cells in the trunk but that it also regulates posterior expression of foxd3 during early development. Further, their work uses cdx mutants and chimeras created via cell transplantation to dive deeper into how cdx4 expression affects trunk NC cell dynamics. Really cool developmental work and we highly recommend checking it out for yourself!
“The epigenetic state of PRDM16-regulated enhancers in radial glia controls cortical neuron position”
For our August journal club we discussed a paper from 2018 from the lab of Dr. Corey Harwell, titled “The epigenetic state of PRDM16-regulated enhancers in radial glia controls cortical neuron position”. This well-rounded paper, which shows how a chromatin-modifying enzyme regulates a neurodevelopmental process, was a crash course for those of us in the lab who are novices in the field of epigenetics.
In the mammalian cerebral cortex, upper layer projection neurons develop in a process whereby radial glia (RG) give rise to intermediate progenitor (IP) cells that divide and then produce pairs of cortical neurons. Previous work showed that PRDM16, a chromatin-modifying enzyme, regulates neural stem cell maintenance and differentiation in the developing brain, and the Harwell group wanted to learn how this protein regulates gene expression in the developing cerebral cortex. Using beautiful immunofluorescent imaging and conditional knock-out (cKO) experiments, PRDM16 expression in RG is shown to promote production of IP cells and upper layer cortical neurons. RNA-seq and ChIP-seq experiments were performed and showed that PRDM16 regulates the transcriptional activation or silencing of genes important for the differentiation of RG into IP cells by epigenetic modification of enhancer regions. The strong activation of the E3 ubiquitin ligase Pdzrn3 in the cKO cortex suggests that it is normally silenced in RG by PRDM16 to promote upper layer cortical neuron migration. This is supported by the rescue of the upper layer cortical neuron defect by knocking down both Prdm16 and Pdzrn3. Finally, more beautiful imaging shows that the histone methyltransferase domain of PRDM16 is required for the silencing of Pdzrn3. Altogether, this paper does a nice job of showing how epigenetic regulation of gene transcription plays a role in setting up neuronal organization in the cortex. Thanks Harwell group for a great paper!
“Inflammation and matrix metalloproteinase 9 (Mmp-9) regulate photoreceptor regeneration in adult zebrafish”
For journal club this week, we read a paper from Dr. Nicholas Silva who published this work last year in Glia, titled “Inflammation and matrix metalloproteinase 9 (Mmp-9) regulate photoreceptor regeneration in adult zebrafish”. These findings came out of his PhD work in the Hitchcock lab at the University of Michigan.
This was a fun zebrafish glia paper with beautiful images and neat techniques (some of us were new to the zymogram!) that investigates how the inflammatory environment affects the ability of Müller glia to proliferate and differentiate into new rods and cones after photoreceptor injury. During this injury response, Müller glia highly express a matrix metalloproteinase, Mmp-9. It turns out that if the glia don’t express mmp9, they increase proliferation and make more photoreceptors. Overproduced rods persist over time, however, cones die. Cone survival can be rescued in mmp9 mutants by suppressing the immune response later in time with dexamethasone, suggesting that Mmp-9’s influence on the inflammatory ‘soup’ affects photoreceptor regeneration.
Of course there’s more twists and turns to the story, so we encourage you to check out the paper for yourself! We look forward to reading Nick’s future work as a postdoc in the Molofsky Lab and beyond.
"A muscle-epidermis-glia signaling axis sustains synaptic specificity during allometric growth in Caenorhabditiselegans”
Today in journal club, the lab discussed a recent study led by Daniel Colón- Ramos published in eLife, entitled “A muscle-epidermis-glia signaling axis sustains synaptic specificity during allometric growth in Caenorhabditis
Glia, genetic tools & confocal imaging in a model organism... All what we love, in one paper!!
As organisms grow to reach their adult size, organs and tissues have to scale up in size too. How do complex neural circuits and synapses that are established during embryogenesis maintain their precise position and
connectivity over such a dramatic change, is a fascinating question. Fan et al found that mig-17, a conserved ADAMTS metalloproteinase secreted from muscles, degrades basement membrane proteins and regulates glial
morphology and position in the worm brain. In turn, these glia that surround the nerve ring regulate synapse positions.
This study underscores the role of non-neuronal cells in maintaining synapse positions during allometric growth of the CNS and reminds us that glia are AWESOME!