Browsing by Subject "Neurogenesis"
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Item Activation of Early Neural Progenitors Is Required for Traumatic Brain Injury-Induced Hippocampal Neurogenesis(2008-09-19) Yu, Tzong-Shiue; Kernie, Steven G.Traumatic brain injury (TBI) is the most common form of acquired brain injury in both children and adults in the United States. TBI causes neuronal loss and results in a variety of neurological impairments and deficits in hippocampus-dependent functions. However, cognitive recovery commonly occurs though the mechanism is unknown. Exploration of post-natal neurogenesis in the hippocampus raises the possibility that adult-born neurons may contribute to cognitive recovery from TBI. Several studies in animal models that mimic TBI demonstrate there is enhanced generation of adult-born neurons in the dentate gyrus and those adult-born neurons may correlate with cognitive recovery. Due to the limits of current methodology in studying neurogenesis, it remains unclear what relevance injury-induced neurogenesis may have in the recovery process following TBI. In order to explore the relevance of injury-induced neurogenesis, I have characterized a previously generated transgenic mouse line that has rtTA-IRES-eGFP expression under the control of a nestin promoter and also contains a neural progenitor-specific regulatory element. By using this line, I have demonstrated that eGFP-expressing cells represent early neural progenitors in the adult dentate gyrus. Performing unilateral controlled cortical injury (CCI) demonstrates that this injury depletes doublecoritn (Dcx)-expressing late neural progenitors while activating eGFP-expressing early neural progenitors. To address whether the subsequent recovery of Dcx-expressing late progenitors was derived from activation of early neural progenitors, I generated a transgenic line that expresses modified herpes simplex viral thymidine kinase (delta-HSV-TK) under the control of the neural progenitor-specific regulatory element of the nestin gene. This allows for temporally regulated ablation of dividing neural progenitors by exposing the animal to ganciclovir. Using this line, I demonstrate that ablation of dividing GFP-expressing early neural progenitors in neurogenic areas occurs only in the presence of ganciclovir. CCI on these mice, reveals that no newly born Dcx-expressing late neural progenitors are observed seven days after injury when exposed to ganciclovir. However, the repopulation of Dcx-expressing cells is apparent when ganciclovir was removed one day before injury. Four weeks after injury, those newly born Dcx-expressing cells became mature NeuN-expressing neurons. This suggests that injury-induced activation of early neural progenitors is required for the recovery of injured hippocampal neurons.Item BDNF-Producing B Cells Mediate Plasticity in the Recovering Brain After Stroke(2021-11-29) Torres, Vanessa; Monson, Nancy L.; Stowe, Ann; Goldberg, Mark P.; Vitetta, Ellen S.; Volk, Lenora J.; Satterthwaite, Anne B.Neuronal networks require significant neurotrophic support for functional plasticity after stroke, but the delivery of neurotrophins has failed thus far in clinical trials. Therefore, identifying endogenous mechanisms that could enhance neurotrophic support in the recovering brain after stroke is essential. B cells, a lymphocyte known to infiltrate the post-stroke brain, possess the ability to produce neurotrophins, including brain-derived neurotrophic factor (BDNF). Depleting B cells after stroke results in motor and cognitive deficits that are mediated by specific brain regions (e.g., hippocampus) outside the initial infarct. We propose that B cells migrate to specific brain regions after stroke and respond to local signals that enhance their neurotrophic capacities to promote neuroplasticity. To investigate whether B cells are a potential source of endogenous BDNF support after stroke, we must identify 1.) the spatial distribution of B cells within the post-stroke brain, 2.) the type of neurotrophic support B cells provide to ischemic-injured neurons and 3.) the impact that the post-stroke microenvironment exerts on the neurotrophic capacity of B cells. Using whole brain microscopy, we discovered that B cells migrate to specific remote brain regions areas outside of the initial infarct that regulate motor and cognitive function after stroke. To understand how B cells support ischemic-injured neurons, we used ex vivo electrophysiology and in vitro models of ischemic injury to assess functional and structural neuroplasticity in the presence or absence of B cells. We discovered that B cells support synaptic transmission in the dentate gyrus region of the hippocampus after stroke and through the production of BDNF, B cells protect against the ischemic-induced loss of neurons and neuronal dendrites. After stroke, neuronal BDNF production is dependent on glutamate-induced activity of the N-methyl-D-aspartate receptor (NMDAR) downstream of the GluN2A subunit. Given that B cells also express NMDARs, we investigated whether glutamate can similarly upregulate BDNF in B cells downstream of their NMDARs. Using microscopy, flow cytometry and qPCR, we discovered that stroke and glutamate differentially regulate B cell gene and surface expression of GluN2A. Additionally, both mouse and human B cells elicit a functional response to glutamate and can induce autocrine BDNF signaling. Collectively, the data presented in this thesis are the first to demonstrate a glutamate-induced neurotrophic role for B cells in the ischemic brain. Understanding the mechanisms by which neuroinflammation supports neuroplasticity after stroke enables the development of immune-based therapeutics that harness endogenous neurotrophic support from B cells to ameliorate pathology.Item Cell Type-Specific Roles of FoxP Transcription Factors in Vocalization and Cognition(2019-07-23) Co, Marissa; Tsai, Peter; Konopka, Genevieve; Johnson, Jane E.; Roberts, ToddMutations of the forkhead domain transcription factors FOXP2 and FOXP1 are highly associated with neurodevelopmental disorders affecting speech and language. Across vertebrate species, their conserved expression patterns in the developing and adult brain predict important functions in neural circuits mediating vocalization and sensorimotor learning. Their known gene targets regulate neuronal development, activity, and plasticity, and animal models of FoxP2 and FoxP1 function have linked some of these molecular functions with neurophysiological and behavioral phenotypes. Still, much remains unknown about molecular networks in the brain driven by these transcription factors, especially in specific regions and cell types. During my dissertation work, I sought to elucidate FoxP2 and FoxP1 functions in cortical, striatal, and cerebellar neurons in mice and zebra finches. This approach of combining comparative genomics with functional studies of salient genes has proven a powerful method for understanding higher cognitive functions such as language (Chapter Two). By characterizing mice lacking cortical Foxp2, I identified its roles in dopamine signaling, interneuron development, and cognitive behavior, but surprisingly not in vocalization (Chapter Three). I further studied the interaction between FoxP2 and its cortical binding partner TBR1, and I found synergistic gene regulation by these transcription factors in neural cells (Chapter Four). I contributed to identification of roles for cortico-hippocampal FoxP1 in cortical development and vocalization (Chapter Five), as well as roles for cerebellar FoxP2 in Purkinje cell morphology, vocalization, and gross motor function (Chapter Six). Finally, I generated tools and datasets to further our understanding of corticostriatal functions of FoxP2 and FoxP1 in vocal learning zebra finches (Chapter Seven). In light of these studies, I discuss their implications for understanding human disorders affecting speech and language, and I impart further hypotheses and recommendations for continuing their study (Chapter Eight). Together, these findings contribute to our knowledge of conserved roles for FoxP2 and FoxP1 in vocal behavior and cognition.Item EPH-B and Ephrin-B Signaling in Migration and Proliferation of Stem Cells(2011-08-10) Catchpole, Timothy; Henkemeyer, MarkIn this dissertation, I investigate the role of Eph-ephrin signaling in the Dentate Gyrus (DG). The DG is a distinctive neuronal structure located in the hippocampus and is one of two areas in the mature brain where stem and progenitor cells reside to continuously produce new neurons throughout adulthood. While Eph-ephrin signaling has been linked to other stem cell populations in the adult, involvement in the progenitor population residing in the hippocampus had not been demonstrated. Here, I establish the expression of B subclass Eph receptors in both embryonic and adult progenitors in the hippocampus. Analysis of EphB1 -/-mutant mice shows that this receptor tyrosine kinase is involved in the regulation of proliferation and polarity of progenitor cells in the neurogenic niche of the DG. Ephrin-B3 acts as a ligand to regulate some aspects of EphB1 activity in the DG. I also show that the EphB2 receptor tyrosine kinase is critical for normal formation of a specific region of the DG known as the lateral suprapyramidal blade (LSB) during late embryonic and early postnatal development. Analysis of intracellular truncation and single amino acid point mutations demonstrates that the tyrosine kinase catalytic activity of EphB2 is essential for LSB formation. This activity is consistent with specific expression of EphB2 in the neural progenitor cells that migrate in a medial direction from the dentate notch of the lateral ventricles to populate and form the DG near the midline of the brain. I further show that ephrin-B1 alone acts as the ligand to activate EphB2 forward signaling in these migrating neural progenitors to contribute to the formation of this vitally important structure. Finally I briefly describe the role of EphB2 forward signaling in stem cell populations beyond the hippocampus. This data demonstrates that Eph-ephrin signaling is intimately involved in both the formation of the neurogenic niche and in the regulation of progenitor cells that occupy that niche.Item Exploring the Role and Sensitivity of the Hippocampal Dentate Gyrus: From Addiction-Relevant Memories to the Influence of Space Radiation on Hippocampal Neurogenesis(2015-04-09) Rivera, Phillip Daniel; German, Dwight; Eisch, Amelia J.; Chen, Benjamin P.; Powell, Craig M.; Zhang, Chun-LiThe hippocampus and its subregion the dentate gyrus (DG) are involved in learning and memory. Adult hippocampal neurogenesis, which takes place in the DG, is also thought to contribute to learning and memory. Understanding the neural basis of learning and memory could help in a wide range of situations, from helping addicts break the cycle of substance abuse to ensuring appropriate astronaut action during spaceflight missions. This doctoral dissertation spans this wide range by using animal models relevant to addiction and spaceflight to improve understanding of the DG and adult neurogenesis, and obliquely, of learning and memory. After an introductory chapter, I show morphine-context reward memories are established via drug/context associations (D/CA, Chapter 2), and require adult neurogenesis for extinction of young reward memories (Chapter 3). Using conditioned place preference, a behavioral test classically used to assess drug strength, and the immediate early gene cFos as an indirect marker of neuronal activity, I found that morphine-paired mice sequestered to a morphine-paired context had more DG cFos+ cells than those sequestered to a saline-paired context or other controls. Thus, the retrieval of D/CA memory is accompanied by activation of hippocampal DG neurons. Surprisingly, image-guided cranial irradiation (IG-IR) prevented extinction of young, but not old, morphine D/CA memories without affecting retrieval. These data suggest that deficits in adult neurogenesis may contribute to stronger D/CA reward memory. The second section of my dissertation (Chapter 4) examines the influence of space radiation on adult neurogenesis. I find acute and fractionated space radiation similarly diminish adult neurogenesis, but neither decrease neural stem cell number, the putative source of new neurons. Thus, while spaceflight mission success may be hampered by space radiation due to diminished neurogenesis, my data raise the possibility that neurogenesis may recover overtime. Taken together, my data show an impaired DG (and perhaps neurogenesis) diminishes extinction of morphine-context reward memories, and that adult neurogenesis is decreased (perhaps reversibly) by space radiation. In my final chapter (Chapter 5), I discuss implications of these data for the fields of learning/memory and neuroscience in general, and suggest future directions that may help addicts recover and allow astronauts to perform optimally during spaceflight missions.Item Investigating the Enteroendocrine - Brain Axis: Ghrelin Cell and ECL Cell Physiology and Ghrelin Action on Mood and Complex Eating(2014-06-11) Walker, Angela Kay; Eisch, Amelia J.; Powell, Craig M.; Scherer, Philipp; Zigman, Jeffrey M.The mechanisms and neurochemical pathways through which the orexigenic peptide hormone ghrelin act to regulate homeostatic feeding is fairly well documented. However, less understood are the mechanisms and brain regions that mediate ghrelin's effects on mood and complex eating behaviors. At the cellular level, little is known about the ghrelin cell's transcriptional profile, its secretory products other than ghrelin, and its relationship to other gastric endocrine cells, such as the histamine producing enterochromaffin-like cell. My doctoral research encompasses multiple aspects of the ghrelin system, from physiological assessments of the ghrelin cell to evaluations of ghrelin action on cue-potentiated feeding and stress-induced depressive-like behavior. Ghrelin has antidepressant effects, which become obvious following chronic stress. In the first part of my thesis, I found that this effect was mediated by neurogenesis. I observed that chronic stress reduces neurogenesis more severely in the ventral dentate gyrus of Ghsr-null mice, suggesting ghrelin provides a level of neuroprotection in the stress environment. Administration of anti-apoptotic P7C3-related compounds not only blocked stress-induced reductions in neurogenesis, but also minimized the severity of depressive-like behavior in mice. Focal hippocampal irradiation prevented the anti-depressant efficacy of P7C3-related compounds, indicating that P7C3 regulates mood directly through neurogenesis. In the second part of my thesis, I designed a novel protocol for studying cue-potentiated feeding behaviors in mice. Absence of ghrelin signaling in Ghsr-null mice, or administration of a ghrelin receptor antagonist in wild-type mice, disrupted the development of normal cue-food associations. Additionally, I discovered Ghsr expression in the basolateral amygdala (BLA), and BLA neuronal activation in response to a food-associated positive cue significantly correlated with amount of food intake. Thus, ghrelin signaling in the BLA may be responsible for its mediation of cue-potentiated feeding behaviors. The third part of my thesis examined the ghrelin cell transcriptome for potential secretory proteins and revealed significant expression of Rbp4, Ttr, and Nucb2, along with RBP4 protein secretion. Lastly, I characterized a novel HDC-Cre mouse model that may be advantageous in future studies to determine potential interactions between histaminergic and ghrelin signaling pathways. The full range of these discoveries advances our comprehensive understanding of ghrelin.Item Neurogenesis and Gliogenesis from Ascl1 (Mash1) Expressing Progenitors in the Central Nervous System(2010-05-14) Kim, Euiseok Joshua; Johnson, Jane E.For the functional architecture of the central nervous system, a small population of neural stem cells generates the correct numbers and types of neurons, oligodendrocytes and astrocytes in a precisely coordinated manner. Basic helix-loop-helix (bHLH) transcription factors play central roles in determining distinct neural cell fates and thus contribute to mechanisms controlling neural cell type diversity during the embryogenesis. Fundamental to understanding nervous system formation is to uncover links between early cell type specification mechanisms, the developmental dynamics of each lineage, and the contributions of specific molecules to these processes to form the mature nervous system structures. Ascl1 (previously Mash1) is a bHLH transcription factor essential for neuronal differentiation and neural sub-type specification. Ascl1 is present in proliferating progenitor cells but these cells are actively differentiating as evidenced by their rapid migration out of germinal zones. Although it has been studied for its role in several neural lineages, the full complement of lineages arising from Ascl1 progenitor cells and the molecular mechanism of Ascl1’s functions are not completely understood. Using an inducible Cre-flox genetic fate-mapping strategy, Ascl1 lineages were determined in both the embryonic and adult central nervous system. In chapter two, the fate of Ascl1+ progenitor cells throughout the brain was described. Depending on the temporal and spatial context during embryogenesis, Ascl1+ cells contribute to distinct neuronal and glial cells in each major brain division. In chapter three, by labeling Ascl1+ progenitor cells at distinct phases of their development, I delineated the temporal lineage relationship of distinct subtypes of neurons and glia in the developing spinal cord. Two spatially and temporally distinct Ascl1+ progenitor populations contribute differentially to inhibitory dILA and excitatory dILB neurons in the dorsal spinal cord. At later stages of embryogenesis, Ascl1+ progenitors are restricted to glial lineages giving rise to both astrocytes and oligodendrocytes. Analysis of conditional mutants of Ascl1 demonstrated that Ascl1 is required for only one division of each lineage. Loss of Ascl1 results in a reduction of inhibitory dILA neurons and oligodendrocytes, but not excitatory dILB neurons and astrocytes. In chapter four, the physiological functions of Nicastrin in gliogenesis were investigated. Nicastrin is a requisite subunit of the !-secretase complex essential for activating Notch signaling pathway. Conditional mutant of Nicastrin leads to the increased level of oligodendrocytes lineage markers in the neural tube, the opposite phenotype of that for Ascl1. Thus, I propose that Notch signaling in constraining levels of Ascl1 is required in oligodendrogenesis. In chapter five, I revealed that Ascl1 is a common molecular marker of early progenitors of both neurons and oligodendrocytes in the adult brain, and these Ascl1 defined progenitors mature with distinct dynamics in different brain regions. In this thesis, I define Ascl1 as a neural differentiation factor crucial for neural cell type diversification, playing important roles in cell differentiation and subtype specification at several different nodes of cell fate decisions throughout neurodevelopment.Item Regulation and Function of PTF1a in the Developing Nervous System(2012-08-15) Meredith, David Miles; Johnson, Jane E.Basic helix-loop-helix transcription factors serve many roles in development, including regulation of neurogenesis. Many of these factors are activated in naive neural progenitors and function to promote neuronal differentiation and cell-type specification. Ptf1a is a basic helix-loop-helix protein that is required for proper inhibitory neuron formation in several regions of the developing nervous system, including the spinal cord, cerebellum, retina, and hypothalamus. In addition, Ptf1a is essential for proper pancreas formation and exocrine function. In both the nervous system and pancreas, Ptf1a functions as a switch in cell fate determination. In the absence of Ptf1a, inhibitory neurons are lost and those cells instead adopt an excitatory identity. Similarly, endodermal progenitors will assume duodenal characteristics in place of a pancreatic identity when Ptf1a is lost. Like most other tissue-specific basic-helix-loop-helix factors, Ptf1a dimerizes with E-proteins and binds a degenerate hexameric E-box motif (CANNTG). Ptf1a is unique, however, in that it also requires the presence of Rbpj(l) to form an active transcription complex, PTF1. This interaction is central to Ptf1a function, as disruption of Ptf1a?s ability to bind Rbpj in vivo phenocopies the Ptf1a null in the nervous system and pancreas. Similarly, all targets described thus far for Ptf1a require an intact PTF1 binding site, which includes both an E-box and Rbpj binding site. In order to understand how a factor such as Ptf1a is capable of giving rise to such disparate organs, I wanted to place it in context of a larger regulatory network that directs a multipotent progenitor into a mature inhibitory neuron. Thus, I examine two regulatory schemes controlling Ptf1a expression during development in Chapters two and three. I then investigate direct Ptf1a targets in a genome-wide fashion using massively parallel sequencing technology in Chapters four and five. These efforts uncovered that Ptf1a employs several mechanisms to achieve proper cell-type specification, including initiation of transcription factor cascades, direct activation of inhibitory neuron machinery, and direct suppression of the excitatory neuron program. Furthermore, I identify novel binding modes and potential co-regulatory factors that could impart tissue-specific function.Item Regulation of Adult Hippocampal Neurogenesis: Insights from Mouse Models of Dementia and Depression(2009-05-13) Donovan, Michael Harry; Eisch, Amelia J.While neurogenesis is largely complete by birth, the subgranular zone (SGZ) in the adult hippocampus continues to produce functional young neurons. The last decade has produced a multitude of research demonstrating that the process of SGZ neurogenesis is dynamically regulated. Stimuli that negatively impact SGZ neurogenesis include stress, depression models, aging and models of neurodegenerative disease. Positive regulators of SGZ neurogenesis include antidepressants and hippocampal-dependent learning. These results have sparked tremendous speculation, both scientific and popular, that adult hippocampal neurogenesis might be critical for mood regulation and/or memory, and might be a promising target for the treatment of depression and dementia. However, we still know little about underlying mechanisms of how increases and decreases in SGZ neurogenesis occur. Here, I examine several manipulations of adult hippocampal neurogenesis, focusing on potential neuromechanisms underlying alterations in SGZ neurogenesis. First, in a mouse model of dementia, I find that in addition to agedependant decline in SGZ proliferation, these mice have retarded migration and maturation of new SGZ neurons and ectopic proliferation in a normally non-neurogenic region. Second, I explore how the antidepressant fluoxetine increases SGZ neurogenesis. I show that the increase occurs only after chronic administration and is not preceded by changes in cell death, cell-cycle or proliferating cell lineage. I next address the capacity of proliferating SGZ cells to respond to brain-derived neurotrophic factor (BDNF), a neurochemical implicated in antidepressant action and neurogenesis regulation. I find that most proliferating cells do not contain the necessary TrkB receptors in vivo, and thus BDNF action is likely indirect or through type-1 stem cells, which contain TrkB. Finally, I look at changes in neurogenesis in a social-defeat depression model. I find that, like other models of repeated stress, social-defeat stress appears to produce a stress-induced decrease in S-phase cells. However, closer analysis reveals that this decrease does not indicate decreased proliferation, and mice that are behaviorally sensitive to the stress actually show an increase in neurogenesis overall. Taken together, these results emphasize the complexity of the processes that comprise adult hippocampal neurogenesis, highlighting the importance of further investigation into the neuromechanisms of changes in neurogenesis.Item The Role of Adult Hippocampal Neurogenesis in Morphine Addiction(2015-04-09) Bulin, Sarah Elizabeth; Hsieh, Jenny; Self, David W.; Powell, Craig M.; Eisch, Amelia J.The hippocampus plays a large role in modulating the reward pathway, being especially important in craving and context-dependent relapse. One form a neuroplasticity within the hippocampus is adult neurogenesis, which occurs in the subgranular zone of the dentate gyrus. While a growing amount of literature has explored the effects of drugs of abuse on adult DG neurogenesis, the relationship between self-administered opiates and adult DG neurogenesis remains unexplored. This dissertation investigates both the role of adult DG neurogenesis in morphine-related behaviors and the effects of self-administered opiates (morphine and heroin) on adult DG neurogenesis. I first explore the background literature important in the work completed within this dissertation (Chapter 1). Next, using a self-administration paradigm, I proceed to show that ablation of adult neurogenesis via cranial irradiation results in increased in morphine intake, decreased extinction, and decreased cognitive flexibility. Additionally, rats lacking adult DG neurogenesis exhibited increased morphine locomotor sensitization with increased DG activation in the infrablade after a low dose morphine challenge (Chapter 2). I will then go on to investigate the consequences of long-term self-administered opiates (morphine and heroin) on the different stages of maturation of adult-generated neurons. I demonstrate that morphine self-administration has no effect on proliferation, survival, or maturation immediately after exposure or after 28 days of withdrawal (Chapter 3). Additionally, I demonstrate that heroin self-administration does not alter DCX+ cell density or granule cell layer volume (Chapter 4). Taken together, my data suggests the adult DG neurogenesis is robust and normally unaffected by self-administered opiates. However, preexisting deficits in DG neurogenesis may lead to an increased vulnerability to addiction-related behaviors. In the final chapter (Chapter 5), I discuss potential implications of this work and future directions in which it may be taken.Item The Role of Adult Neurogenesis in Cocaine Addiction(2009-01-14) Noonan, Michele Ann; Eisch, Amelia J.New neurons are born in the adult hippocampus in a region known as the subgranular zone (SGZ). This process is dynamically regulated and new neurons are thought to be important for certain types of spatial learning and memory. Proliferation of SGZ neural progenitors is decreased by drugs of abuse, yet it is not clear how the type and amount of drug as well as the pattern of administration changes long-term effects on neurogenesis. In addition, it is unclear what role if any SGZ neurogenesis plays in initiating drug-taking or relapse behaviors, or whether changes in neurogenesis are merely side effects of drug-taking. I first examined effects of chronic cocaine self-administration and withdrawal on the different stages of neurogenesis. I found an early deficit in proliferation of neural progenitors, as well as a 4 week delayed increase in doublecortin-positive (DCX+) immature neurons which were common to both rats in withdrawal or those continuing to self-administer cocaine. I next asked the question of the functional consequence of changes in adult hippocampal neurogenesis to the acquisition and maintenance of drug-taking, as well as relapse to drug-taking. I found that reduced adult neurogenesis via cranial irradiation prior to cocaine-taking was associated with increased acquisition of drug-taking and increased motivation for cocaine, but not sucrose, while reduced adult neurogenesis after rats have acquired cocaine self-administration was associated with increased resistance to extinction of drug-seeking behavior. Finally, I asked if formation of drug-context associations would be altered in rodents with reduced neurogenesis in a passive drug exposure paradigm. I found that a transgenic mouse with reduced adult neurogenesis has impaired long-term drug-context memory in the cocaine conditioned place preference paradigm (CPP). Together these findings suggest that reduced adult hippocampal neurogenesis is a risk factor for drug addiction, that decreased proliferation after chronic drug intake likely contributes to drug-taking and drug-seeking behaviors, and that the delayed increase in immature neurons after drug-taking is likely protective against relapse. In sum, increases in adult hippocampal neurogenesis are beneficial both to the naïve and addicted brain, and therapeutics specifically increasing adult neurogenesis could aid in preventing initial addiction as well preventing future relapse.Item The Role of Glutamate Transporters in Early Postnatal Hippocampal Neurogenesis(2011-02-01) Gilley, Jennifer A.; Kernie, Steven G.Adult neurogenesis has been well-characterized in the subgranular zone (SGZ) of the hippocampal dentate gyrus however, early postnatal development of the dentate gyrus and changes in the neurogenic niche during this time have not been well-studied. Using a well-characterized transgenic mouse that labels early neural progenitor cells with green fluorescent protein (GFP), we created a developmental profile of the dentate gyrus from postnatal day seven (P7) to six months of age. In addition, we determined that early progenitor populations within the developing dentate gyrus exhibit age-dependent changes in proliferation and differentiation which are controlled by cell-autonomous cues. To identify potential regulators of these phenotypes, we performed microarrays and identified several differentially expressed genes within the progenitor pools of different aged mice. GltI, a glutamate transporter, was identified as a candidate which was upregulated 10 fold in progenitors from older animals. In astrocytes, GltI and Glast are required to maintain low levels of glutamate to prevent overstimulation of glutamate receptors. In neural precursors it has been suggested that glutamate stimulates proliferation by activating metabotropic glutamate receptors (mGluRs) which leads to increased intracellular calcium, however the function of glutamate transporters on these progenitors has not been identified. To elucidate the functional role of GltI and Glast, we performed in vitro experiments in glutamate-free media. By misexpressing GltI and Glast, we show that glutamate transporters negatively regulate calcium-dependent proliferation by controlling glutamate availability to mGluRs. To address the in vivo function of glutamate transporters in injury-induced neurogenesis, we characterized their expression after hypoxic-ischemic (HI) injury and noticed prolonged upregulation of both transporters on type I cells suggesting they may be involved in hypoxic preconditioning. To address this we induced expression of glutamate transporters with HI before exposing mice to traumatic brain injury (TBI). Compared to animals only injured with TBI, mice with both injuries displayed decreased progenitor proliferation suggesting an impaired capacity for repair. We have therefore identified a novel and clinically relevant role for GltI and Glast in progenitor proliferation during development and after injury.Item Role of Mash1-E Protein Heterodimers in Mash1 Function in the Developing Neural Tube(2003-05-01) Collisson, Tandi Louise; Lu, Q. RichardNeural-specific Class II bHLH transcription factors heterodimerize with ubiquitous Class I bHLH E proteins to form complexes required for neural differentiation. There are four known E proteins, HEB, E12, E47 and E2.2, in the mammalian nervous system, which potentially form heterodimers with Mash1 in the neural tube. To test the relevance of particular Mash1-E protein heterodimer combinations in vivo, I constructed tethered Mash1-E protein heterodimers for over-expression in the chick neural tube. By comparing overexpression of Mash1 with over-expression of these Mash1-E protein heterodimers, their abilities to effect neural differentiation and cell-type specification were analyzed. Mash1-E protein heterodimers are interchangeable in the function of driving neurogenesis in the chick neural tube. The effects of Mash1-E protein heterodimers on cell-type specificity were different, suggesting non-redundant functions in effecting dorsal interneuron populations. Furthermore, additional Mash1 heterodimer partners may be required for the cell-type specification function of Mash1.Item The Role of NeuroD1 in Physiological and Pathological Neurogenesis(2016-12-05) Brulet, Rebecca R.; Schneider, Jay W.; Hsieh, Jenny; Eisch, Amelia J.; Ge, Woo-PingNeurogenesis in the adult brain is a complex and highly regulated process. Under normal physiological conditions neurogenesis in the hippocampal subgranular zone (SGZ) is important for learning, memory, and mood regulation. What is not well understood, however, is whether in certain disease contexts, like epilepsy, aberrant neurogenesis can contribute to the progression of spontaneous reoccurring seizures (SRS) and associated memory decline. In this work, I present evidence that aberrant hippocampal neurogenesis is causative in the perpetuation of SRS. In an effort to target a select stage of adult neurogenesis I identified the bHLH transcription factor NeuroD1, known to be important in adult neurogenesis, as being strongly upregulated after status epilepticus (SE). Additionally, I show expression of NeuroD1 in aberrant ectopically localized granule cells suggesting a potential role for this transcription factor in the progression of epilepsy. NeuroD1 conditional knockout (cKO) in progenitor cells of the hippocampus may be sufficient to reduce the number of immature and mature neurons amongst the labeled population, however the total number of immature and mature neurons was not significantly changed aside from the immature neurons ectopically localized to the hilus. Consistent with this, the total SRS was unchanged in the NeuroD1 cKO. Transdifferentiation, or the direct inter-lineage conversion of adult somatic cells is a powerful tool with the potential to be used in neuronal replacement strategies in certain neurological disorders or CNS injuries. Transdifferentiation of reactive astrocytes into glutamatergic neurons via retroviral targeting in the cortex can be accomplished by overexpression of the transcription factor NeuroD1. However, what is not well understood is whether the state of reactive gliosis is necessary to "prime" these cells for the transdifferentiation process. In this work I present evidence to suggest that overexpression of NeuroD1 in the absence of reactive gliosis is capable of astrocyte to neuron transdifferentiation, however the total number of converted cells is vastly lower than what was previously published, suggesting that reactive gliosis does indeed enhance and facilitate the conversion process.Item Roles of Ascl1 and Olig2 in the Transcriptional Regulation of Astrocytogenesis(2016-01-19) Combiths, Adam; Vue, Tou Yia; Johnson, Jane E.Ascl1 and Olig2 are transcription factors highly expressed in certain neural progenitor cells, and are known to be involved in neurogenesis and oligodendrogenesis (OL) throughout the CNS; their role in astrocytogenesis (AS) is less well explored. Recent evidence shows that Ascl1-lineage AS clones in the spinal cord (SC) are spatially restricted to either gray matter (GM) or white matter (WM), but not both, and that Olig2 may be necessary for WM astrocytogenesis in the brain. We consider the following questions: (1) Do Ascl1+ progenitors give rise to astrocytes in the brain? (2) Do astrocyte clones, in general, display the GM/WM spatial restriction seen in Ascl1-lineage astrocytes? (3a) Is Olig2 expressed by astrocytes in the SC? (3b) If it is, is this expression required for astrocytogenesis in the SC? To address (1), we used the CreERT2 system under the Ascl1 promoter to label Ascl1+ progenitor cells in the neonatal murine brain (and their progeny) with the tdTom fluorescent reporter. Adult brains were obtained and immunohistochemically (IHC) labeled for factors specific to mature AS, OL and neural lineages; AS, OL, and neurons derived from neonatal Ascl1+ progenitors were observed in every major cortical and subcortical structure, showing that neonatal Ascl1+ progenitors do give rise to AS through the brain. To address (2), we used the CreERT2-Confetti system under the promoter for hGFAP (an astrocyte-specific marker) to give sparse labeling of astrocytes in multiple colors, so that any clone (one clone representing all the progeny of a single AS-progenitor cell) will be far from and visually distinct from other clones. Adult murine SCs were obtained, sectioned, and analyzed by fluorescence microscopy. The location, morphology and clonal identity of every labeled cell was cataloged and used to construct a clonal map of AS distribution in the spinal cord from neonatal development through adulthood, revealing the presence of "mixed" (non-GM/WM-restricted) AS clones - strong evidence for the existence of a GM/WM bipotent AS progenitor cell. To address (3a), we used the CreERT2 system under hGFAP, and IHC labeled for the presence of Olig2. The presence of Olig2+;tdTom+ double positive cells (i.e., astrocytes expressing Olig2) was quantified via fluorescence microscopy. Approximately 50% of astrocytes expressed Olig2. To address (3b), we repeated the above procedure in mice with floxed Olig2 alleles, allowing conditional knockout (CKO) of Olig2 at time of induction. 50% of Olig2-CKO spinal cords showed an almost-complete lack of astrocytes, tentatively indicating a vital role of Olig2 expression in astrocytogenesis in both the GM and the WM.Item Sensory Neurogenesis and the Role of PRDM12 in Nociceptor Development and Function(August 2021) Landy, Mark Andrew; Johnson, Jane E.; Henkemeyer, Mark; Price, Theodore; Lai, HelenNociceptors are a set of peripheral neurons responsible for the detection of noxious stimuli. They function to alert us to the presence of potentially damaging internal and environmental threats, thereby playing an important role in allowing us to react and avoid danger. Unfortunately, for over 30% of the population, the sense of pain derived from nociception becomes maladaptive, leading to chronic painful conditions which carry an estimated economic burden of over USD 600 billion. While opioids are the current mainstay analgesic medication, they have a vast array of side effects, including risk of overdose and death, which makes their use in treatment of chronic conditions far from ideal. Recently, studies of genetic mutations leading to congenital insensitivity to pain (CIP) have provided a springboard for the development of novel analgesics targeting nociceptor function in the periphery. The identification of additional such mutations in the gene Prdm12 raised questions about processes inherent to nociceptor development and sensory neurogenesis as a whole, and what function this gene plays in mature primary afferent neurons. Over the course of my dissertation work I sought to address some of these questions by studying the development of nociceptive neurons in mice, and the effect of Prdm12-knockout on pain sensation. To establish a framework for sensory neuronal development, I first completed a birthdating study using a thymidine analog to permanently label cells undergoing their final mitotic divisions and identify them at later timepoints. With this, I show that there is no temporal difference in the birth rates of different nociceptor subtypes, but that most are born after touch and proprioceptive neurons. Next, using multiple models to knockout Prdm12 at various timepoints ranging from conception to adulthood, I then provide evidence that this is a key transcription factor for specification of the nociceptor population, but that its function likely changes over time. Loss of Prdm12 during development causes defects in nociception, but no behavioral phenotype was readily discernible following adult knockout. Instead, I show that Prdm12 appears to regulate a population of stem cell-like neurons, with an as-yet unknown role in dorsal root ganglia. Altogether my work highlights the role of Prdm12 in nociceptor development and lays the groundwork for additional studies to investigate the clinical relevance of this gene.Item Simulated Space Radiation: Effects on Murine Behavior and Neurogenesis(2018-04-17) Whoolery, Cody William; German, Dwight; Stowe, Ann; Eisch, Amelia J.; Shay, Jerry W.; Burma, SandeepAn unavoidable consequence of deep space exploration is exposure to high-atomic number, high-energy (HZE) particles, such as 28Si or 56Fe, that comprise galactic cosmic radiation (GCR). It is widely believed that GCR is damaging to the brain, as HZE particle exposure decreases rodent hippocampal dentate gyrus neurogenesis as well as function (e.g. learning and memory). While this raises concern that GCR will compromise astronaut health and mission success, most data have been collected using a specific set of parameters: 2 month old mice or rats (age-equivalent to a teenage human) irradiated with 56Fe. For this dissertation, I have filled three major knowledge gaps with regards to space radiation, brain, and behavior, which are described in the five chapters of my dissertation. In my introductory chapter, Chapter 1, I provide the essential background needed to understand the research chapters, including an overview of the hippocampus, the process of neurogenesis and how radiation affects it, and in-depth look at the published literature on how space radiation influences the central nervous system (CNS). In Chapter 2, I present my published work (Whoolery et al. 2017) on how dentate gyrus neurogenesis is changed at two timepoints post-28Si irradiation (24 h and 3 months), and explain how 28Si-induced changes in dentate gyrus neurogenesis compares to the effects seen after exposure to other previously-studied ions. In Chapter 3, I present my submitted work on how dentate gyrus-dependent behaviors are changed after 6 month old mice are exposed to mission-relevant doses of 56Fe. I test mice on many behavioral paradigms, but the most striking results come from two pattern separation tasks: the aversive Contextual Discrimination Fear Conditioning (CDFC) task and the appetitive Location Discrimination (LD) task which is performed on the Lafayette Bussey touchscreen platform. As I show in Chapter 3, mice exposed to 56Fe radiation display surprisingly improved performance on both CDFC and LD, findings which are discussed in relation to mission-critical behaviors and prior results on space radiation-induced changes in behavior. In Chapter 4, I expand on the operant touchscreen data provided. Specifically, I investigate whether the 56Fe-induced improvement in pattern separation is transient and if it is sex-specific. In my conclusion chapter, Chapter 5, I summarize the main conclusions of Chapters 2-4, provided future directions for each project, possible mechanisms that may underlie this improvement in pattern separation, and end with my thoughts on remaining challenges in the field and obstacles that need to be overcome.Item Transcriptional Regulation of Adult Neurogenesis by NRSF/REST and NeuroD1(2011-08-10) Ure, Kerstin Maria; Hsieh, JennyNeurogenesis in the adult brain is a complex and lifelong process that is regulated by multiple pathways and is sensitive to many external stimuli. Two critical regulatory factors in this process are NRSF/REST and NeuroD1. NRSF/REST, a transcriptional repressor that binds a specific NRSE site and recruits corepressors and chromatin remodeling machinery to repress its target genes, is critical for maintenance of the neural stem cell pool and for proper pacing of neuronal differentiation. NeuroD1, a bHLH transcription factor, is necessary for the terminal differentiation, maturation, and survival of newborn neurons. In addition, both factors are necessary for the neurogenic response to both physiological and pathological stimuli, which may induce neurogenesis through different pathways. Thus, NRSF/REST and NeuroD1 are necessary for neurogenesis to occur correctly, to persist throughout the organism’s lifespan, and to respond to external stimuli.Item [UT Southwestern Medical Center News](2010-03-31) Ladson, LaKishaItem [UT Southwestern Medical Center News](2012-03-08) Wormser, Deborah