Abstract
Whether the apical dendrite emerges by transformation of the leading process of the migrating neuron or emerges de novo after migration is completed is unclear. Similarly, it is not clear whether the secreted glycoprotein Reelin controls migration and dendritic growth as related or separate processes. Here, multiphoton microscopy reveals the direct transformation of the leading process into the apical dendrite. This transformation is coupled to the successful completion of migration and neuronal soma arrest occurs below the first stable branch point of the nascent dendrite. Deficiency in Reelin causes the forming dendrite to avoid its normal target area and branch aberrantly, leading to improper cellular positioning. Therefore, this study links Reelin-dependent dendritogenesis with migration arrest and cortical lamination.
Highlights
Excitatory projection neurons in the cortex are highly polarized, having an apical dendrite and descending axon
Dashed lines represent the lower boundary of the marginal zone (MZ)/SPP (ϳ15 m) and cortical plate (CP) (ϳ50 m) in A and B
Much is known about dendritic initiation in other contexts, including cultured hippocampal neurons (Dotti and Banker, 1987; Dotti et al, 1988; Niu et al, 2004; MacLaurin et al, 2007), for actively migrating cortical neurons in situ, it was unclear whether the apical dendrite emerges via direct transformation of the leading process or emerges de novo in the postmigratory period (Ramon y Cajal, 1904)
Summary
Excitatory projection neurons in the cortex are highly polarized, having an apical dendrite and descending axon Student support was provided by the SUNY Upstate College of Graduate Studies, Department of Neuroscience and Physiology, Syracuse, New York. We thank Michael Frotscher (University of Freiburg) for the stable cell line expressing Reelin; Mary Beth Hatten (Rockefeller University) for providing the Gensat Pde1C::eGFP mice; Teiichi Furuichi (Tokyo University of Science) for the pCAGGSmRFP plasmid; Roger Tsien (University of California, San Diego) for the tdTomato plasmid; Rebecca Sager and Ryan Curl for help in neuron tracing and quantification; Diana Norman for aid in data visualization; Judson Belmont and Tina Lupone for technical support and animal management; Peter Calvert, Brian Howell, and Rick Matthews for comments and suggestions regarding the experiments, data analysis, and data visualization/presentation; and Robert Quinn and the staff in the Department of Laboratory Animal Resources for animal care.
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