Ira B. Black - US grants

The proposed research is an extension of ongoing studies on the plasticity of the nervous system during development, maturity and old age. Using molecular genetic, immunocytochemical, biochemical and pharmacologic techniques, we have found that extracellular signals regulate neurotransmitter metabolism, and may actually alter neurotransmitter phenotypic expression by neurons during development and maturity. We have begun to define trans-synaptic molecular messages and their trophic effects in the neonate and adult nervous system. We are now using in vivo and tissue culture approaches to define the specific molecular messages that govern neurotransmitter plasticity throughout life. The present studies will focus on the molecular mechanisms regulating neuronal plasticity in the peripheral nervous system and brain. More specifically, we hope to a) define molecular genetic mechanisms underlying phenotypic plasticity in neonatal sympathetic neurons, using cDNA probes; b) define the scope and basis of plasticity in adult neurons; c) determine the basis of deficits in plasticity that we have recently defined in aged neurons; d) define molecular genetic mechanisms underlying trans-synaptic regulation of transmitter development, and trans-synaptic regulation of transmitter enzymes during maturity; e) define molecular genetic mechanisms underlying independent regulation of different neurohumoral systems within the same cell, using cDNA to proenkephalin and tyrosine hydroxylase in the adrenal medulla; f) determine how neuronal aggregation alters transmitter phenotypic expression; g) define mechanisms by which nerve growth factor regulates development and maintenance of specific subpopulations of brain neurons, a recent finding in our laboratory. These studies then are directed toward understanding neuronal and synaptic plasticity at the molecular level.

The central goal of this program project is to elucidate integrative principles regulating brain development by defining sequential ontogenetic processes. We are pursuing the unifying concept that seemingly distinct developmental processes, including neuronal mitosis, aggregation, transmitter and receptor gene expression and trophic interactions with the formation of synaptic circuits are causally interrelated. Although several of these events have been examined in some detail, causal mechanistic relationships among these processes remain unclear. Our studies are now defining critical interactions among these phenomena. We are finding that a number of molecules integrate successive developmental processes through intercellular communication. We will employ multidisciplinary molecular genetic, biochemical, pharmacologic and morphologic approaches to study neuronal development in vivo and in culture. We plan to define a) factors regulating neuronal mitosis, focusing on insulin, a neuronal mitogen recently identified by us; b) regulation of expression of the NGF (nerve growth factor) receptor gene, recently cloned by us; c) mechanisms governing transmitter receptor expression; d) membrane factors governing transmitter phenotypic expression and e) NGF regulation of the formation of brain circuits. Our overall objective is to define molecular mechanistic relations among these apparently diverse developmental processes. Such insights may indicate how seemingly discrete, sequential events causally lead to orderly brain development. This information may define molecular loci where disease processes intervene, leading to abnormal brain development, birth defects and mental retardation.

DESCRIPTION (provided by applicant): The central objective of this program project is to define integrative principles governing the diverse processes of brain development and plasticity. We hypothesize that reciprocal stem cell differentiation, and neuron-neuron and neuron-Glial-neuron interactions, mediated by a limited set of inter- and intra-cellular signals, coordinate gene expression and seemingly unrelated developmental events. Moreover, specific genes, such as Rab3A, regulate trophin-induced synaptic plasticity. Specifically: a) trophic factors, including the diffusible neurotrophin gene family members, b) growth (mitogenic) factors, including bFGF and IGF-1, mediated by cyclins, CDKs and CKIs, c) membrane-bound cellular labels of the Eph gene family, d) neurotransmitters and the hormone, estradiol and e) the newly discovered intracellular trophin transduction molecule ARMS, working combinatorially, synchronize the developmental sequence. These molecular signals coordinate stem cell commitment and differentiation, neuronal mitosis, selective survival, axonal pathfinding, topographic projection, synaptogenesis and synaptic plasticity. We will employ multidisciplinary molecular genetic, transcriptional, biochemical and morphologic approaches at the population and single cell levels to study development and plasticity in vivo and in culture. We plan to define a) epigenetic regulation of stem cell and precursor mitosis and differentiation, b) the roles of bFGF and IGF-1 in cortical development, c) the role(s) of ARMS in mediating p75 and trk neurotrophin receptor actions in development and plasticity, d) the actions of Eph ligands and receptors in axon defasciculation and synaptogenesis in targets, e) trophic regulation of genes at the single cell level regulating synaptic plasticity and synaptogenesis, and f) the role of astrocyte-neuron interactions in brain development.