Diverse modes of axon elaboration in the developing neocortex

Portera-Cailliau, Carlos, Weimer, Robby M., De Paola, Vincenzo, Caroni, Pico, Svoboda, Karel (August 2005) Diverse modes of axon elaboration in the developing neocortex. PLoS Biol, 3 (8). e272. ISSN 1545-7885 (Electronic)

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DOI: 10.1371/journal.pbio.0030272

Abstract

The development of axonal arbors is a critical step in the establishment of precise neural circuits, but relatively little is known about the mechanisms of axonal elaboration in the neocortex. We used in vivo two-photon time-lapse microscopy to image axons in the neocortex of green fluorescent protein-transgenic mice over the first 3 wk of postnatal development. This period spans the elaboration of thalamocortical (TC) and Cajal-Retzius (CR) axons and cortical synaptogenesis. Layer 1 collaterals of TC and CR axons were imaged repeatedly over time scales ranging from minutes up to days, and their growth and pruning were analyzed. The structure and dynamics of TC and CR axons differed profoundly. Branches of TC axons terminated in small, bulbous growth cones, while CR axon branch tips had large growth cones with numerous long filopodia. TC axons grew rapidly in straight paths, with frequent interstitial branch additions, while CR axons grew more slowly along tortuous paths. For both types of axon, new branches appeared at interstitial sites along the axon shaft and did not involve growth cone splitting. Pruning occurred via retraction of small axon branches (tens of microns, at both CR and TC axons) or degeneration of large portions of the arbor (hundreds of microns, for TC axons only). The balance between growth and retraction favored overall growth, but only by a slight margin. Given the identical layer 1 territory upon which CR and TC axons grow, the differences in their structure and dynamics likely reflect distinct intrinsic growth programs for axons of long projection neurons versus local interneurons.

Item Type: Paper
Uncontrolled Keywords: Animals Axons/physiology/ ultrastructure Female Green Fluorescent Proteins/analysis Growth Cones/physiology/ultrastructure Male Mice Mice, Transgenic Microscopy, Fluorescence, Multiphoton Neocortex/cytology/ growth & development Promoter Regions (Genetics) Recombinant Fusion Proteins/analysis
Subjects: organs, tissues, organelles, cell types and functions > cell types and functions > cell types > dendritic cells > dendritic arbors
organs, tissues, organelles, cell types and functions > cell types and functions > cell types > dendritic cells > dendritic arbors
organs, tissues, organelles, cell types and functions > cell types and functions > cell types > dendritic cells > dendritic arbors

Investigative techniques and equipment > microscopy > flourescence microscopy > two-photon excitation microscopy
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Depositing User: CSHL Librarian
Date: August 2005
Date Deposited: 09 Jan 2012 15:00
Last Modified: 09 Jan 2012 15:00
URI: http://repository.cshl.edu/id/eprint/22676

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