Frances Lefcort - US grants

growth factor receptors; receptor expression; neurogenesis; neurotrophic factors; cell growth regulation; spinal ganglion; developmental neurobiology; protein isoforms; cell differentiation; neural crest; apoptosis; innervation; tissue /cell culture; Aves; transfection; immunologic assay /test; immunocytochemistry;

DESCRIPTION: (Adapted from the applicant's Application) A central question in developmental biology is how a multicellular organism can arise from a single cell. In an effort to understand the complexity of the restricted expression of specific subsets of genes to a particular cell or tissue type, the investigators have compared the transcriptomes (the set of expressed genes) and propose to initiate preliminary studies to determine the feasibility of comparing the proteomes (the set of proteins) of immature and mature chicken dorsal root ganglia (DRG). The objective is to determine the function of a differentially expressed molecule, neural epidermal growth-factor like (NEL), and to extend the analysis of molecular differences to the proteome level. Specific Aim 1 proposes to determine the function of NEL during sensory neurogenesis. Specific Aim 2 plans to determine the molecular differences in the proteomes between immature and mature DRG. A proteomic analysis will be initiated by running 2D gels on E4.5 and E8.5 DRG and, based on their resolution, the feasibility of this approach will be determined. If successful, the investigators can conduct protein identification through mass spectrometric analysis.

DESCRIPTION (provided by applicant): The sensory neurons of the dorsal root ganglia (DRG) are a heterogeneous cell population that subserve such diverse modalities as pain, temperature, touch, pressure and proprioception. Yet all of these cells derive from a common pool of neuroepithelial progenitors which emigrate from the neural tube. How is such diversity in cell phenotype established? In hereditary peripheral neuropathies, aspects of this developmental sequence go awry; intriguingly, often only specific subsets of sensory neurons are deficient. For example, Familial Dysautonomia is marked by a diminution in the sensory neurons that mediate pain and temperature. Furthermore, in adult onset peripheral neuropathies, specific subsets of DRG sensory neurons degenerate. Thus an elucidation of the critical events which comprise the development of each sensory neuron subclass is required in order to develop therapeutic strategies for targeting the specific compromised subpopulation. Both extrinsic, environmental signals and inheritable cues govern the establishment of cell phenotype. Thus the goal of this proposal is to determine the role of lineage in determining the identity of subclasses of sensory neurons in addition to identifying the extrinsic factors which regulate this process. A major outstanding question is whether there are distinct subclasses of mitotically-active progenitor cells within the nascent DRG that give rise to discrete subtypes of sensory neurons. We propose to identify and characterize the subtypes of progenitor cells resident within the DRG by conducting a lineage analysis, and to identify the extrinsic factors that regulate their proliferation, survival, and/or differentiation. Our lab has provided strong evidence for a role for neurotrophins (NT-3), CNTF, PACAP and NELL2 in regulating the proliferation and differentiation of subsets of DRG progenitor cells. However, it is evident that other extrinsic factors are operative during DRG development. Based on their prominent role in multiple systems and our preliminary investigations of their expression, we propose to determine the function of a major class of receptor tyrosine kinase family, the chick homologues of Axl/tyro3/mer family: c-eyk and rek, during DRG development using in ovo misexpression analyses. Fulfillment of these aims will enhance our understanding of the cellular and molecular mechanisms that sculpt the genesis and differentiation of discrete cell types within a neura tissue.

DESCRIPTION (provided by applicant): The sensory neurons of the dorsal root ganglia (DRG) are a heterogeneous cell population that subserve such diverse modalities as pain, temperature, touch, pressure and proprioception. Yet all of these cells derive from a common pool of neuroepithelial progenitors which emigrate from the neural tube. How is such diversity in cell phenotype established? In hereditary peripheral neuropathies, aspects of this developmental sequence go awry; intriguingly, often only specific subsets of sensory neurons are deficient. For example, Familial Dysautonomia is marked by a diminution in the sensory neurons that mediate pain and temperature. Furthermore, in adult onset peripheral neuropathies, specific subsets of DRG sensory neurons degenerate. Thus an elucidation of the critical events which comprise the development of each sensory neuron subclass is required in order to develop therapeutic strategies for targeting the specific compromised subpopulation. Both extrinsic, environmental signals and inheritable cues govern the establishment of cell phenotype. Thus the goal of this proposal is to determine the role of lineage in determining the identity of subclasses of sensory neurons in addition to identifying the extrinsic factors which regulate this process. A major outstanding question is whether there are distinct subclasses of mitotically-active progenitor cells within the nascent DRG that give rise to discrete subtypes of sensory neurons. We propose to identify and characterize the subtypes of progenitor cells resident within the DRG by conducting a lineage analysis, and to identify the extrinsic factors that regulate their proliferation, survival, and/or differentiation. Our lab has provided strong evidence for a role for neurotrophins (NT-3), CNTF, PACAP and NELL2 in regulating the proliferation and differentiation of subsets of DRG progenitor cells. However, it is evident that other extrinsic factors are operative during DRG development. Based on their prominent role in multiple systems and our preliminary investigations of their expression, we propose to determine the function of a major class of receptor tyrosine kinase family, the chick homologues of Axl/tyro3/mer family: c-eyk and rek, during DRG development using in ovo misexpression analyses. Fulfillment of these aims will enhance our understanding of the cellular and molecular mechanisms that sculpt the genesis and differentiation of discrete cell types within a neura tissue.

DESCRIPTION (provided by applicant): A major goal in clinical and basic neuroscience is to identify factors that can promote the survival of spinal motor neurons. Despite the identification of several neurotrophic factors that can support motor neurons, we are still incapable of rescuing the majority of motor neurons in vivo. The goal of this proposal is to determine the function of a relatively novel receptor tyrosine kinase, Anaplastic Lymphoma Kinase (ALK), in spinal motor neurons. Based on our preliminary data including the fact ALK is dynamically expressed in spinal motor neurons during the period of programmed cell death (PCD), we hypothesize that ALK promotes the survival of spinal motor neurons. We will test this hypothesis by conducting gain and loss-of-function manipulations of ALK expression chick embryos in ovo and determine the effects on spinal motor neuron survival. PUBLIC HEALTH RELEVANCE: If spinal motor neurons die, paralysis results. Motor neurons die in developmental disorders such as Spinal Muscular Atrophy and in adult-onset disorders such as Amyotrophic Lateral Sclerosis (Lou Gehrig's disease) and following spinal cord injury. We have identified a protein, Anaplastic lymphoma kinase, which is expressed on spinal motor neurons. Our preliminary data indicates that reducing levels of this protein causes the death of spinal motor neurons. The goal of this study is to increase levels of this protein to test whether we can rescue dying spinal motor neurons. This work could lead to novel therapeutics for promoting the survival of motor neurons in neural disease.

DESCRIPTION (provided by applicant): The goal of this proposal is to understand why reductions in the level of the IKAP protein cause the Hereditary Sensory and Autonomic Neuropathy Type III, Familial Dysautonomia (FD; also called Riley Day Syndrome). This disease is both a developmental and a progressive disorder. It is marked by tachycardia, orthostatic hypotension which results in frequent fainting and autonomic vomiting crises, pulmonary problems, renal failure and musculoskeletal manifestations including scoliosis, ataxia and weakness. This disease not only devastates the functioning of the Autonomic Nervous System, but also is marked by severe deficits in pain and temperature sensation and has CNS manifestations. FD is due to a mutation in the gene IKBKAP, in a splice acceptor site (IVS20+6T>C; 99.5% of patients) that causes the transcription of a truncated mRNA which is targeted for nonsense-mediated decay. The function of the encoded protein, IKAP, is unresolved. It clearly plays an essential role in that mice that are completely null for Ikbkap die by E10 due to failure in neurulation and vasculogenesis. To determine what role IKAP serves in the nervous system and why its absence results in FD, we have made 2 conditional-knock out mouse models for the disease in which Ikbkap is deleted either from the neural crest (using a Wnt1-cre), or from neurons in the central nervous system (CNS), but not the peripheral nervous system (PNS; using a Ta1tubulin-cre). The Wnt1-cre/Ikbkap mice die within 24 hrs of birth and analyses of their PNS demonstrates a recapitulation of the human disease with significant reductions in sympathetic, parasympathetic and TrkA+ pain and temperature sensing neurons and thus provides an excellent model for determining the developmental disruptions in the disease. We found that the reduction in PNS neurons during development is due to apoptosis of both progenitor cells and post-mitotic neurons. The Ta1tubulin-cre/Ikbkap also faithfully recapitulates classic, but distinct, hallmarks of FD including scoliosis, hind limb weakness, and gait ataxia. These mice die on average at 5 months and their condition degenerates as they age, thus they provide an excellent system in which to study the progressively degenerative mechanisms that mark FD. These results indicate not only is deletion of Ikbkap in the nervous system sufficient to cause FD, but that we have two independent models in which we can dissect the functions of IKAP in the CNS and PNS, during development vs. progression in the adult. Since the Autonomic Nervous system (ANS) is a circuit that includes both CNS and PNS components, we propose here to take a system wide approach to determine the function of IKAP in both the CNS and PNS. With an understanding of the key pathways which require IKAP, the long term goal is to develop strategies to prevent the progressive degeneration of both CNS and PNS neurons in FD and the other HSANs.

PROJECT SUMMARY Given the recent FDA approval of targeted AAV gene therapy platforms and of small-molecule splicing modulators as treatments for genetic neurological disorders, our goal is to apply these powerful technologies to prevent the progressive optic neuropathy and blindness that develops in patients with the genetic recessive disease, Familial dysautonomia (FD). FD results from a splice site mutation in intron 20 of the gene ELP1 (formerly called IKBKAP). As a consequence of the mis-splicing, exon 20 is variably skipped, the mutant mRNA degraded, resulting in reduced levels of the encoded protein, Elp1.. Interestingly, the ability to splice the mutated pre-mRNA varies according to tissue type, with neurons least capable of splicing the mutated pre- mRNA. While the majority of the clinical deficits are due to the devastation of the sensory and autonomic nervous systems, as patients enter their teens, their macular retinal ganglion cells progressively die, manifesting as visual loss. Mouse that are null for Elp1 are embryonic lethal so the field has, until now, taken two distinct strategies to generate mouse models to investigate FD: (i) generation of conditional knock-out mice (CKO) using cell-type specific cre-driven promoters; and (ii) transgenic mice that contain the human FD ELP1 splicing mutation. The former approach has generated mouse models that recapitulate the FD optic neuropathy that results from the progressive death of retinal ganglion cells. These mice are an excellent pre- clinical model for testing the effectiveness of gene therapy for preventing the progressive demise of retinal ganglion cells (Aim 1A). However this model does not lend itself to testing the effectiveness of splicing enhancer compounds since it lacks the FD splicing mutation. The latter approach has culminated in the generation of transgenic mice that include copies of the human FD ELP1 mutated gene. These mice are asymptomatic unless they are crossed to a hypomorph or null background mouse, but these compound mice are typically too sick to investigate consistently. Here we will make a new ?hybrid? line by crossing in the human FD ELP1 mutated gene into our retina-specific CKO line (Pax6-cre;Elp1flox/flox) to overcome these major challenges to the field. In so doing, we will generate a single mouse model that manifests the human FD optic neuropathy, in an otherwise healthy background, and contains the splice site mutation, which can be used to test a variety of therapeutic approaches (Aim1A, B). The overall aim of this proposal is to assess and compare two methods for restoring normal levels of the Elp1 protein in this new model mouse retinae using: (i) AAV2- mediated gene therapy (gene reintroduction) of the wild type Elp1 gene injected intravitreously, and (ii) a novel splicing enhancer compound that has been shown to promote the inclusion of exon 20 in the mutant FD gene in the retina, delivered orally through diet. Our goal is to test which method best mitigates the death of retinal ganglion cells in addition to interrogating whether a combination of both methods (Aim 1C) will have additive effects on promoting the survival of retinal ganglion cells, given they work via two distinct pathways.