The long-range objectives of these stuidies is to gain an understanding of the developmental factors that lead to the orderly, laminar arrangement of neurons within the visual cortex, and the complex set of neuronal connections that determine its function. In our recent work we have provided the first description of fibronectin(FN)-like immunoreactivity in the developing neocortex of the mouse in a distribution that suggests a role in guiding the ingrowth of cortical afferents or in the consolidation of the cortical plate. We have developed a monoclonal antibody, 2Al, which recognizes a developmentally regulated cellsurface antigen (2Al-A) specific to CNS neurons that may be involved in cellsubstrate or cell-cell adhesion. In tissue culture, 2A1-A is prcminent on qrowth cones and at points of neurite-neurite contact and fasciculation. In the present application, we propose a series of in vivo and in vitro studies to answer the following questions: 1. Is FN a component of the substrate traversed by growth cones of early-arriving cortical afferents or in the migratory pathway of cells that form the cortical plate? We will carry out an immno-electron microscopic determination of the relationship between FN-like immunoreactivity, growth cones, and migrating neurons in the developing cortex. 2. Which cellular elements in the developing cortex produce or sequester FN? We will identify cortical cells producing FN in vitro with cell-type specific antibodies, and use in situ hybridization to identify cortical cells producing FN mRNA in vivo. 3. Is the epitope recoqnized by 2Al carried on a ganglioside? Does the location of 2Al-A suggest that it forms a link between cells, between fasciculating axons, or between growth cones and their substrate? We will characterized 2Al-A biochemically, use immuno- EM to lccalize 2A1-A in the embryonic cortex, and use in vitro assays to determine whether neurite outgrowth and fasciculation are altered by Fab fragments of 2A1 and whether advancing neurites adhere to or avoid substrates coated with 2Al-A. 4. Do radial glia and early cortical neurons have common precursor? Does the common precursor persist after neuronal and glial phenotypes appear? What is the fate of the transient population of radial glia? We will use a recombinant retroviral lineage marker to determine the early lineage relationships of neurons and glia in vitro, and cell-type specific antibody markers to determine whether radial glia are transformed into astrocytes.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Visual Sciences B Study Section (VISB)
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Washington University
Schools of Medicine
Saint Louis
United States
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Sheppard, A M; Pearlman, A L (1997) Abnormal reorganization of preplate neurons and their associated extracellular matrix: an early manifestation of altered neocortical development in the reeler mutant mouse. J Comp Neurol 378:173-9
Miller, B; Sheppard, A M; Pearlman, A L (1997) Developmental expression of keratan sulfate-like immunoreactivity distinguishes thalamic nuclei and cortical domains. J Comp Neurol 380:533-52
Pearlman, A L; Sheppard, A M (1996) Extracellular matrix in early cortical development. Prog Brain Res 108:117-34
Miller, B; Sheppard, A M; Bicknese, A R et al. (1995) Chondroitin sulfate proteoglycans in the developing cerebral cortex: the distribution of neurocan distinguishes forming afferent and efferent axonal pathways. J Comp Neurol 355:615-28
Sheppard, A M; Brunstrom, J E; Thornton, T N et al. (1995) Neuronal production of fibronectin in the cerebral cortex during migration and layer formation is unique to specific cortical domains. Dev Biol 172:504-18
Bicknese, A R; Sheppard, A M; O'Leary, D D et al. (1994) Thalamocortical axons extend along a chondroitin sulfate proteoglycan-enriched pathway coincident with the neocortical subplate and distinct from the efferent path. J Neurosci 14:3500-10
Baumrind, N L; Parkinson, D; Wayne, D B et al. (1992) EMA: a developmentally regulated cell-surface glycoprotein of CNS neurons that is concentrated at the leading edge of growth cones. Dev Dyn 194:311-25
Sheetz, M P; Wayne, D B; Pearlman, A L (1992) Extension of filopodia by motor-dependent actin assembly. Cell Motil Cytoskeleton 22:160-9
Sheppard, A M; Hamilton, S K; Pearlman, A L (1991) Changes in the distribution of extracellular matrix components accompany early morphogenetic events of mammalian cortical development. J Neurosci 11:3928-42
Sheetz, M P; Baumrind, N L; Wayne, D B et al. (1990) Concentration of membrane antigens by forward transport and trapping in neuronal growth cones. Cell 61:231-41

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