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The generation of cellular diversity during early development of nervous system is poorly understood. In the Drosophila central nervous system, cell diversity is primarily generated by the invariant lineage of neural precursors called neuroblasts. It has been proposed that a class of genes are expressed in neuroblasts and their progeny and control the cell lineage of each neuroblast. I used an enhancer trap screen to identify the ming gene, which is transiently expressed in a subset of neuroblasts at reproducible points in their cell lineage (i.e. in neuroblast sublineages), suggesting that neuroblast identity can be altered during its cell lineage. ming encodes a predicted zinc finger protein within the TFIIIA superfamily. Loss of ming function results in altered CNS expression of the engrailed gene, defects in axonogenesis and embryonic lethality. I propose that ming, as a neuroblast sublineage gene, controls distinct cell fates within neuroblast cell lineages. I investigate the precise temporal regulation of the sublineage gene expression. I show that four genes (ming, even-skipped, unplugged and achaete) are expressed in specific neuroblast sublineages. I show that these neuroblasts can be identified in embryos lacking both neuroblast cytokinesis and cell cycle progression (string mutants) and in embryos lacking only neuroblast cytokinesis (pebble mutants). I find that the unplugged and achaete genes are expressed normally in string and pebble mutant embryos, indicating that temporal control is independent of neuroblast cytokinesis or counting cell cycles. In contrast, neuroblasts require cytokinesis to activate sublineage ming expression, while a single, identified neuroblast requires cell cycle progression to activate even-skipped expression. These results suggest that neuroblasts have an intrinsic gene regulatory hierarchy controlling unplugged and achaete expression, but that cell cycle- or cytokinesis-dependent mechanisms are required for ming and eve CNS expression.
The generation of cellular diversity during early development of nervous system is poorly understood. In the Drosophila central nervous system, cell diversity is primarily generated by the invariant lineage of neural precursors called neuroblasts. It has been proposed that a class of genes are expressed in neuroblasts and their progeny and control the cell lineage of each neuroblast. I used an enhancer trap screen to identify the ming gene, which is transiently expressed in a subset of neuroblasts at reproducible points in their cell lineage (i.e. in neuroblast sublineages), suggesting that neuroblast identity can be altered during its cell lineage. ming encodes a predicted zinc finger protein within the TFIIIA superfamily. Loss of ming function results in altered CNS expression of the engrailed gene, defects in axonogenesis and embryonic lethality. I propose that ming, as a neuroblast sublineage gene, controls distinct cell fates within neuroblast cell lineages. I investigate the precise temporal regulation of the sublineage gene expression. I show that four genes (ming, even-skipped, unplugged and achaete) are expressed in specific neuroblast sublineages. I show that these neuroblasts can be identified in embryos lacking both neuroblast cytokinesis and cell cycle progression (string mutants) and in embryos lacking only neuroblast cytokinesis (pebble mutants). I find that the unplugged and achaete genes are expressed normally in string and pebble mutant embryos, indicating that temporal control is independent of neuroblast cytokinesis or counting cell cycles. In contrast, neuroblasts require cytokinesis to activate sublineage ming expression, while a single, identified neuroblast requires cell cycle progression to activate even-skipped expression. These results suggest that neuroblasts have an intrinsic gene regulatory hierarchy controlling unplugged and achaete expression, but that cell cycle- or cytokinesis-dependent mechanisms are required for ming and eve CNS expression.
The timing of cell production by progenitor cells is an essential aspect of development. Particularly during neurogenesis, the time at which neurons and glia are produced affects their function and proper integration into neural circuits. In both the mammalian and Drosophila central nervous system, neural progenitors progressively lose competence to make early-born cell types, so that "old" progenitors can no longer be induced to make "young" neurons. My dissertation work used Drosophila neural progenitors, known as neuroblasts, as a model to investigate the restriction of neural progenitor competence. Drosophila neuroblasts sequentially express temporal transcription factors (TTFs) that determine neural and glial cell fate based on birth-order. For example, the second TTF in the series, Kruppel, is necessary and sufficient for all second-born / third-born fates, regardless of cell type or neuroblast lineage. However, neuroblasts lose competence to respond to Kruppel with each division, ultimately completely losing competence to produce Kruppel-specified cell types at late stages of development. I discovered that chromatin remodeling complexes of the Polycomb group are necessary and sufficient for the temporal restriction of neuroblast competence. I found that Polycomb complexes establish distinct competence windows in neuroblasts that transition from early motorneuron production to late interneuron production. This work provides a mechanistic basis for the restriction of neuroblast competence and supports a model in which Polycomb complexes progressively limit the ability of TTFs to activate gene expression programs that induce early-born fates
Determinants of Neuronal Identity brings together studies of a wide range of vertebrate and invertebrate organisms that highlight the determinants of neuronal identity. Emphasis of this book is on how neurons are generated; how their developmental identities are specified; and to what degree those identities can be subsequently modified to meet the changing needs of the organism. This book also considers various techniques used in the analysis of different organisms. This volume is comprised of 15 chapters; the first of which introduces the reader to the specification of neuronal identity in Caenorhabditis elegans. The discussion then turns to neurogenesis and segmental homology in the leech, as well as intrinsic and extrinsic factors influencing the development of Retzius neurons in the leech nervous system. Drosophila is discussed next, with particular reference to neuronal diversity in the embryonic central nervous system, cell choice and patterning in the retina, and development of the peripheral nervous system. Other chapters explore endocrine influences on the postembryonic fates of neurons during insect metamorphosis; neuron determination in the nervous system of Hydra and in the mammalian cerebral cortex; and segregation of cell lineage in the vertebrate neural crest. This book will help scientists and active researchers in synthesizing a conceptual framework for further studies of neuronal specification.
The fruit fly Drosophila melanogaster offers the most powerful means of studying embryonic development in eukaryotes. New information from many different organ systems has accumulated rapidly in the past decade. This monograph, written by the most distinguished workers in the field, is the most authoritative and comprehensive synthesis of Drosophila developmental biology available and emphasizes the insights gained by molecular and genetic analysis. In two volumes, it is a lavishly illustrated, elegantly designed reference work illustrating principles of genetic regulation of embryogenesis that may apply to other eukaryotes.
The fruitfly Drosophila melanogaster is an ideal model system to study processes of the central nervous system This book provides an overview of some major facets of recent research on Drosophila brain development.
The interaction between biology and evolution has been the subject of great interest in recent years. Because evolution is such a highly debated topic, a biologically oriented discussion will appeal not only to scientists and biologists but also to the interested lay person. This topic will always be a subject of controversy and therefore any breaking information regarding it is of great interest.The author is a recognized expert in the field of developmental biology and has been instrumental in elucidating the relationship between biology and evolution. The study of evolution is of interest to many different kinds of people and Genomic Regulatory Systems: In Development and Evolution is written at a level that is very easy to read and understand even for the nonscientist.* Contents Include* Regulatory Hardwiring: A Brief Overview of the Genomic Control Apparatus and Its Causal Role in Development and Evolution * Inside the Cis-Regulatory Module: Control Logic and How the Regulatory Environment Is Transduced into Spatial Patterns of Gene Expression* Regulation of Direct Cell-Type Specification in Early Development* The Secret of the Bilaterians: Abstract Regulatory Design in Building Adult Body Parts* Changes That Make New Forms: Gene Regulatory Systems and the Evolution of Body Plans