2005 |
Kohwi, Minoree |
F31Activity Code Description: To provide predoctoral individuals with supervised research training in specified health and health-related areas leading toward the research degree (e.g., Ph.D.). |
Molecular Mechanisms Underlying Adult Svz Neurogenesis @ University of California San Francisco
DESCRIPTION (provided by applicant): Neural stem cells reside in the subventricular zone (SVZ) of adult mammals continuously producing multiples types of olfactory bulb (OB) interneurons. The generation of diverse types of neurons within the adult brain must be tightly regulated in order to maintain a functional circuit with high turnover of its neuronal components; however, the molecular mechanism underlying generation of such diversity is unknown. Our recent data shows that the transcription factor Pax6 is required for the generation of dopaminergic OB interneurons. The expression of another factor Er81 in a distinct pattern from Pax6 in the adult OB suggests that different transcriptional machineries may function in the production of OB interneuron subtypes. In this application, we aim to determine which OB interneuron subtype requires Er81. We also plan to analyze which embryonic progenitor zones can contribute to OB neurogenesis to gain insight into the molecular players of adult neuronal diversity. Thirdly, we aim to compare the molecular expression profiles of adult neural stem cells. Understanding the mechanism underlying neuronal diversity within the brain will be important for future therapies to replace damaged neurons in diseases and trauma.
|
0.969 |
2012 — 2016 |
Kohwi, Minoree |
K99Activity Code Description: To support the initial phase of a Career/Research Transition award program that provides 1-2 years of mentored support for highly motivated, advanced postdoctoral research scientists. R00Activity Code Description: To support the second phase of a Career/Research Transition award program that provides 1 -3 years of independent research support (R00) contingent on securing an independent research position. Award recipients will be expected to compete successfully for independent R01 support from the NIH during the R00 research transition award period. |
Mechanisms Underlying Loss of Neural Stem Cell Competence.
DESCRIPTION (provided by applicant): In both vertebrates and invertebrates, a vast diversity of neurons is generated from a relatively small pool of neural stem cells that undergo stereotyped temporal transitions to ensure that each cell type is made at the right time and in the right quantities. These transitions are highly regulated to ensure the development of a functional brain. Over time, neural stem cells lose competence to specify earlier-born fates; thus specific neuronal cell types can be generated only during a specific developmental time window. The mechanisms of how this occurs are totally unknown, but have wide implications in understanding the basic rules of brain development and how developmental brain disorders may arise. We have chosen to address this question in Drosophila, in which each of the ~30 neuroblasts (neural stem cells) gives rise to distinct lineages, but always in a stereotyped birth order. This order is specified by the neuroblasts' sequential expression of a series of temporal identity factors as they divide. The zinc-finger transcription factor, Hunchback (Hb) specifies first-born progeny, and consequently these neurons transcribe hb. First-born fate, characterized by hb transcription, can be specified for only a limited time during what is called the early competence window, best characterized in neuroblast 7-1. Afterwards, the neuroblast can no longer respond to ectopic Hb expression to produce progeny that transcribes hb, suggesting epigenetic mechanisms may underlie competence loss. I recently established DNA fluorescent in situ hybridization (DNA-FISH) on whole-mount Drosophila embryo neuroblasts to track the subnuclear position of the hb gene. I found a robust repositioning of the hb gene from the nuclear interior in young neuroblasts to the nuclear periphery in older neuroblasts. Strikingly, th timing of hb gene repositioning to the nuclear periphery, generally associated with silent genes, is coincident with the end of the neuroblast 7-1 early competence window. Furthermore, the nuclear factor Distal antenna (Dan), which we found can extend neuroblast 7-1 competence, inhibits this gene repositioning. Based on the above observations, I hypothesize that genome reorganization underlies loss of competence and Dan functions in neuroblasts to establish a early competence genome architecture. Recent evidence indicates that Ikaros, the Hb orthologue in mammals, establishes early competence in mouse retinal progenitor cells, which undergo transitions between competence states to generate distinct progeny in a stereotyped birth order. Work on Ikaros function in hematopoietic stem cells suggest that perhaps chromatin organization may underlie transitions between competence states in retinal progenitors. I further propose to translate my work in Drosophila to the mouse retina model system to investigate the mechanisms underlying loss of competence during mammalian development. Together, the above information will provide crucial insight into the origins of neural diversity and have wide implications in harnessing stem cells for tissue replacement therapies. PUBLIC HEALTH RELEVANCE: Project Narrative Health Relevance The goal of this project is to determine how different types of neural cells are produced during development. The results from the proposed experiments will provide important insight into 1) the basic mechanisms underlying brain development and how disorders in brain development can arise, and 2) how stem cells can be harnessed to replace specific types of brain cells lost during damage or disease.
|
1 |
2017 — 2021 |
Kohwi, Minoree |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Regulation of Neural Progenitor Competence @ Columbia University Health Sciences
In both insects and mammals, a relatively small group of neural progenitors gives rise to diverse neural cells which must be made at the right time, place, and abundance to form a functional brain. Neural progenitors sequentially make distinct cell types in an invariant order, and over time they lose potential (or ?competence?) to specify earlier-born cell fates as they acquire competence to generate the later-born fates. Thus, competence is a fundamental property of progenitors that ensures the production of particular cell types at the right developmental stages. How competence transitions are regulated and how they are developmentally timed is largely unknown. We propose to study these mechanisms, which will be highly impactful in our fundamental understanding of brain development and origin of neurodevelopmental disorders. The Drosophila embryo is an ideal system to uncover mechanisms regulating progenitor competence, because of the ability to track single neural lineages over time and the large number of genetic tools available. In the embryonic nerve cord there are ~30 distinct neuroblasts (NBs, neural progenitors), and each generates a unique lineage of neural cells. Cell fate is specified based on birth order, with successive NB divisions sequentially expressing the transcription factors Hunchback (hb), Kruppel, Pou domain protein, and Castor. The neural progeny in turn maintain active transcription of these factors indefinitely. NB competence to specify early-born fate is restricted to a limited time window, and we found the window closes when the hb genomic locus relocates to the nuclear lamina, where it is permanently silenced. We hypothesize that NB competence is regulated through global reorganization of genome architecture, and that synergistic activity of cell-intrinsic and extrinsic factors determines the developmental timing of competence restriction. To study the mechanisms underlying NB competence restriction, we will examine the function of two nuclear factors that we discovered regulate the length of the NB competence window. Further, using new tools we have generated to profile NBs at specific developmental stages, we will explore changes in the epigenetic landscape and global gene-lamina associations of NBs over time. In particular, we will study whether the hb gene's epigenetic status prior to relocation to the nuclear lamina is required to ?prime? the gene for silencing or whether lamina-tethering is sufficient for competence loss. Our model system is ideally suited to address this question, because we have precise information of the hb gene's transcriptional state, subnuclear gene localization, and NB competence at each cell division. Finally, we found that the steroid hormone Ecdysone plays a role in NB competence, and we will examine how this global extrinsic signal regulates the developmental timing of competence restriction. Together, our proposed studies will provide novel insights into the basic mechanisms of neural progenitor competence regulation and how it is coordinated through time and space.
|
1 |