title: Visualization of corticofugal projections during early cortical development in a tau-GFP-transgenic mouse.
abstract: The first postmitotic neurons in the developing neocortex establish the preplate layer. These early-born neurons have a significant influence on the circuitry of the developing cortex. However, the exact timing and trajectory of their projections, between cortical hemispheres and intra- and extra-cortical regions, remain unresolved. Here, we describe the creation of a transgenic mouse using a 1.3 kb golli promoter element of the myelin basic protein gene to target expression of a tau-green fluorescent protein (GFP) fusion protein in the cell bodies and processes of pioneer cortical neurons. During embryonic and early neonatal development, the timing and patterning of process extension from these neurons was examined. Analysis of tau-GFP fluorescent fibers revealed that progression of early labeled projections was interrupted unexpectedly by transient pauses at the corticostriatal and telencephalic-diencephalic boundaries before invading the thalamus just prior to birth. After birth the pioneering projections differentially invaded the thalamus, excluding some nuclei, e.g. medial and lateral geniculate, until postnatal days 10-14. Early labeled projections were also found to cross to the contralateral hemisphere as well as to the superior colliculus. These results indicate that early corticothalamic projections appear to pause before invading specific subcortical regions during development, that there is developmental regulation of innervation of individual thalamic nuclei, and that these early-generated neurons also establish early projections to commissural and subcortical targets.
authors.affiliation: UCLA Semel Institute for Neuroscience, 635 Charles E Young Drive South, Los Angeles, CA 90095-7332, USA.
authors.forename: Erin C
authors.initials: EC
authors.lastname: Jacobs
authors.forename: Celia
authors.initials: C
authors.lastname: Campagnoni
authors.forename: Kathy
authors.initials: K
authors.lastname: Kampf
authors.forename: Samuel D
authors.initials: SD
authors.lastname: Reyes
authors.forename: Vikram
authors.initials: V
authors.lastname: Kalra
authors.forename: Vance
authors.initials: V
authors.lastname: Handley
authors.forename: Yuan-Yun
authors.initials: YY
authors.lastname: Xie
authors.forename: Yan
authors.initials: Y
authors.lastname: Hong-Hu
authors.forename: Vilma
authors.initials: V
authors.lastname: Spreur
authors.forename: Robin S
authors.initials: RS
authors.lastname: Fisher
authors.forename: Anthony T
authors.initials: AT
authors.lastname: Campagnoni
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001931:Brain Mapping; D002452:Cell Count / Q000379:methods; D002540:Cerebral Cortex / Q000166:cytology / Q000196:embryology* / Q000254:growth & development* / Q000378:metabolism; D004622:Embryo, Mammalian; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D051379:Mice; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009434:Neural Pathways / Q000196:embryology / Q000254:growth & development / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D016875:tau Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D009419:Nerve Tissue Proteins; D016875:tau Proteins; D049452:Green Fluorescent Proteins