Browsing by Author "Kuo, Chay T"

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Open Access
Cysteine proteinase-1 and cut protein isoform control dendritic innervation of two distinct sensory fields by a single neuron.
(Cell Rep, 2014-03-13) Lyons, Gray R; Andersen, Ryan O; Abdi, Khadar; Song, Won-Seok; Kuo, Chay T
Dendrites often exhibit structural changes in response to local inputs. Although mechanisms that pattern and maintain dendritic arbors are becoming clearer, processes regulating regrowth, during context-dependent plasticity or after injury, remain poorly understood. We found that a class of Drosophila sensory neurons, through complete pruning and regeneration, can elaborate two distinct dendritic trees, innervating independent sensory fields. An expression screen identified Cysteine proteinase-1 (Cp1) as a critical regulator of this process. Unlike known ecdysone effectors, Cp1-mutant ddaC neurons pruned larval dendrites normally but failed to regrow adult dendrites. Cp1 expression was upregulated/concentrated in the nucleus during metamorphosis, controlling production of a truncated Cut homeodomain transcription factor. This truncated Cut, but not the full-length protein, allowed Cp1-mutant ddaC neurons to regenerate higher-order adult dendrites. These results identify a molecular pathway needed for dendrite regrowth after pruning, which allows the same neuron to innervate distinct sensory fields.
Open Access
Ependymal Planar Cell Polarity in the SVZ Neurogenic Niche
(2016-05-10) Zerihun, Liilian
In this study, we mapped stages in the development of planar cell polarity in 3 ages of infant mice (3, 8, and 11 days post-partum). We found an increasing asymmetry, ventral alignment, and transition from disorganized to organized ciliary beating. Next, we explored the effect of healthy-tissue modulation on the normally developing planar cell polarity. Modulation of previously healthy tissue mirrors the effect of sudden-onset diseases like stroke and brain injury. Both environmental and biochemical modulations were produced in-vitro. We found that healthy developing ependymal cells were sensitive to these changes. Removal of fluid flow led to loss of asymmetrical planar polarity, loss of cilia, and more disorganized ciliary beating. Suppression of FOXJ1, an important biochemical transcription factor, in previously healthy immature cells led to loss of cilia and greater misalignment of basal bodies.
Open Access
Modeling the Integration Potential of Postnatal Neural Stem Cell Progeny
(2015) Luciano, Dominic
Postnatal subventricular zone (SVZ) neurogenesis in the rodent generates large numbers of neuroblasts that migrate and integrate daily into the mature olfactory bulb (OB) circuit. After brain injury and stroke, neural stem cells (NSCs) within the SVZ niche generate neuroblasts that migrate to the site of injury, thus providing a potential endogenous source of cells to replace those lost from injury. Given the paucity of treatment options after stroke, it is widely believed in the field that enhancing neurogenesis after injury has promise for providing future treatment. Despite the promise of endogenous NSCs for repair, in health the degree to which SVZ neuroblasts have the capability to integrate outside of their normal development in the olfactory bulb (OB) remains an open question. After brain injury, the progeny produced by NSCs after stroke remains poorly understood. My research has focused on identifying the NSC response to injury, and modeling SVZ neuroblasts' intrinsic integration capabilities.
Using nestin-CreERtm4 NSC lineage tracing we identified that NSCs produce a specialized Thbs4hi population of astrocytes. Photothrombotic cortical injuries result in Thbs4hi astrocyte generation, rather than neuroblast production in NSCs. In Thbs4KO/KO mice SVZ astrogenesis is ablated with neuroblasts instead migrating to the site of injury. With the observation of large numbers of neuroblasts at the injury site, we wanted to model the integration potential of SVZ derived neuroblasts without normal development. Using a novel live imaging assay, I found neuroblast maturational state is associated with distinct migratory properties and apical dendrite targeting ability. Microarray analyses of SVZ neuroblasts during migration show significant changes in gene expression profiles from birth to just prior to circuit integration in the OB. Furthermore, I present evidence that newborn SVZ interneurons require Ankyrin3 (Ank3) for precise action potential generation and survival in the OB. After photothrombotic cortical injuries, neuroblasts that migrate to the injury site are unable to upregulate Ank3.
These research presents a novel insight into the on the cellular identity of the NSC response to injury, and understanding how neuroblast development influences SVZ neuroblasts integration capabilities. New directions from this study include, additional study of Thbs4hi astrocytes' role after injury. Additionally, great progress can be made using the gene expression data to optimize neuroblast integration in health and after injury. Understanding the processes of NSC injury response and neuroblast integration will provide useful insight into nervous system function.
Open Access
Molecular Mechanisms of Sensory Neuron Dendrite Remodeling
(2012) Lyons, Gray R
Dendrites are the primary sites of information input into neurons. Proper establishment and maintenance of dendritic structure is essential for the function of neural circuits. In response to certain stimuli, the shape of dendritic arbors may be refined and remodeled. Despite the importance of dendrite structural plasticity in health and disease, the molecular mechanisms governing this process are not well understood. One genetically tractable platform to study context-dependent remodeling is the Drosophila peripheral nervous system. A subset of sensory neurons, the class IV dendritic arborizing neurons, has been shown to prune and regrow dendrites during metamorphosis. My research has focused on the mechanism through which these neurons regenerate a morphologically distinct dendritic structure. A forward genetic protein trap screen was conducted to identify genes differentially expressed during metamorphosis compared to larval stages. I identified Cysteine proteinase-1 as a gene upregulated in class IV neurons during dendrite regeneration under control of ecdysone hormone. Neurons carrying mutations of Cysteine proteinase-1 were unable to target and elaborate secondary dendritic arbors, resulting in disrupted morphology. These data were found to phenocopy dendrite regeneration defects in neurons lacking the homeobox transcription factor cut. Furthermore, I present evidence that Cysteine proteinase-1 can regulate a truncated cut isoform with altered function. This research presents a novel insight into the molecular mechanisms of sensory neuron dendrite remodeling. New directions arising from this study include potential conservation of this mechanism across species, downstream effectors of identified genes, and characterization of other systems subject to context-dependent dendrite regeneration. Elucidating the processes regulating dendrite remodeling will provide useful insight into nervous system function in health and disease.
Open Access
Protective astrogenesis from the SVZ niche after injury is controlled by Notch modulator Thbs4.
(Nature, 2013-05) Benner, Eric J; Luciano, Dominic; Jo, Rebecca; Abdi, Khadar; Paez-Gonzalez, Patricia; Sheng, Huaxin; Warner, David S; Liu, Chunlei; Eroglu, Cagla; Kuo, Chay T
Postnatal/adult neural stem cells (NSCs) within the rodent subventricular zone (SVZ; also called subependymal zone) generate doublecortin (Dcx)(+) neuroblasts that migrate and integrate into olfactory bulb circuitry. Continuous production of neuroblasts is controlled by the SVZ microenvironmental niche. It is generally thought that enhancing the neurogenic activities of endogenous NSCs may provide needed therapeutic options for disease states and after brain injury. However, SVZ NSCs can also differentiate into astrocytes. It remains unclear whether there are conditions that favour astrogenesis over neurogenesis in the SVZ niche, and whether astrocytes produced there have different properties compared with astrocytes produced elsewhere in the brain. Here we show in mice that SVZ-generated astrocytes express high levels of thrombospondin 4 (Thbs4), a secreted homopentameric glycoprotein, in contrast to cortical astrocytes, which express low levels of Thbs4. We found that localized photothrombotic/ischaemic cortical injury initiates a marked increase in Thbs4(hi) astrocyte production from the postnatal SVZ niche. Tamoxifen-inducible nestin-creER(tm)4 lineage tracing demonstrated that it is these SVZ-generated Thbs4(hi) astrocytes, and not Dcx(+) neuroblasts, that home-in on the injured cortex. This robust post-injury astrogenic response required SVZ Notch activation modulated by Thbs4 via direct Notch1 receptor binding and endocytosis to activate downstream signals, including increased Nfia transcription factor expression important for glia production. Consequently, Thbs4 homozygous knockout mice (Thbs4(KO/KO)) showed severe defects in cortical-injury-induced SVZ astrogenesis, instead producing cells expressing Dcx migrating from SVZ to the injury sites. These alterations in cellular responses resulted in abnormal glial scar formation after injury, and significantly increased microvascular haemorrhage into the brain parenchyma of Thbs4(KO/KO) mice. Taken together, these findings have important implications for post-injury applications of endogenous and transplanted NSCs in the therapeutic setting, as well as disease states where Thbs family members have important roles.