What makes an axon an axon?

November 10, 2008

Inside every axon is a dendrite waiting to get out. Hedstrom et al. converted mature axons into dendrites by banishing a protein crucial for neuron development. The results suggest that this transformation could occur after nerve cell damage.

The study, to be published in the Nov. 17 issue of the Journal of Cell Biology, will be available online Nov. 10.

At the junction between the axon and the cell body is the axon initial segment (AIS), which sparks action potentials. Researchers also suspect that the AIS enables an axon to maintain its identity. Although scientists have teased out some of the molecular events that determine whether a neuron outgrowth will become an axon or a dendrite, they know little about what keeps these structures distinct.

In cultured neurons, Hedstrom et al. used RNAi to cut production of ankyrinG, a protein that helps spur formation of the AIS. Loss of ankyrinG caused the AIS to disappear. For example, sodium channels that normally crowd the AIS's plasma membrane dispersed. When ankyrinG was absent the erstwhile axons began to resemble dendrites, sprouting spines and developing excitatory synapses. Characteristic molecules from the cell body and dendrites, such as the microtubule polymerizing protein MAP2, also infiltrated the axons.

The AIS appears to serve as a filter that screens out dendritic proteins, Hedstrom et al. conclude. How the structure bars some proteins from the axon is still uncertain. Injuries and diseases can transform dendrites into axons. The findings raise the possibility that these insults could cause the reverse transformation by changing the amount of ankyrinG and altering the AIS.

Rockefeller University Press

---

---

	From Axons to Identity: Neurological Explorations of the Nature of the Self (Norton Series on Interpersonal Neurobiology) by Todd E. Feinberg (Author) A leading neuroscientist offers an intriguing scientific journey to understanding the neurobiology of the self.What can dementia, delusions, and other neurological disorders teach us about how the brain creates personal identity and a unified sense of self? Here, a leading neurobiologist offers an intriguing scientific approach to understanding the neurobiology of the self. Drawing on both the latest neuroscientific research, as well as the author's decades of experience with neurological patients, From Axons to Identity examines the link between brain and identity in fascinating new ways. Dr. Feinberg presents case studies of individuals with brain pathologies and unusual psychiatric syndromes that cause them to deny parts of their bodies or believe in the presence of...
	Cell Biology of the Axon (Results and Problems in Cell Differentiation) by Edward Koenig (Editor) Recent years have witnessed striking advances in research on axons at a cellular level that substantially impact our current understanding of axonal biology. Newer findings and their ramifications are critically reviewed in the 16 chapters of this volume by authors highly qualified by virtue of their scientific contributions to research areas they know and write about. Five basic areas (I to V) germane to axonal biology are highlighted, beginning with (I) signaling interactions mediating myelination, and differentiation of axonal membrane domains; (IIa) issues surrounding organization and transport dynamics of neurofilaments in axons, (IIb) mechanisms regulating microtubule organization and dynamics, misregulation of which causes axonal degeneration, and (IIc) the roles actin binding...
	Essays in Literature and Ethics: Edited With a Biographical Introduction by William E. A. Axon (1889) by William Anderson O'Conor (Author) Originally published in 1889. This volume from the Cornell University Library's print collections was scanned on an APT BookScan and converted to JPG 2000 format by Kirtas Technologies. All titles scanned cover to cover and pages may include marks notations and other marginalia present in the original volume.
	Axon Growth and Guidance (Advances in Experimental Medicine and Biology) by Dominique Bagnard (Editor) This book proposes an updated view of the current knowledge of the molecular and cellular mechanisms ensuring axon growth and guidance. The introductory chapter will remind the readers of all the features of a growth cone and the mechanisms controlling its growth. From there, one enters a fabulous journey with a growth cone, a Tom Thumb story filled with molecular encounters and complex interactions leading to one of the most fantastic developmental achievements: the nervous system wiring.
	Gastroenterological Endoscopy by Anthony Axon (Author), John Baillie (Author), Hugh Barr (Author), Kenneth Binmoeller (Author) Gastroenterological endoscopy has experienced tremendous advancements in the last decade. In this outstanding book, you'll get state-of-the-art information on all therapeutic developments and innovations in the field. A top team of highly acclaimed gastroenterology specialists from around the world have come together under the editorial leadership of Meinhard Classen, Guido N.J. Tytgat, and Charles J. Lightdale to create this pace-setting atlas and reference work. The book gives you complete coverage of everything from basic examination techniques to the latest treatment strategies in gastroenterology. You'll learn how to recognize diseases and reach an accurate diagnosis for disorders of the GI tract. More that 1,800 illustrations, most in full-color, demonstrate theories...
	Let's Go to a Stock Exchange, by Gordon V. Axon (Author) When they visit a stockbroker's office, two children learn about the functions of a stockbroker, the differences between stocks and bonds, and the operation of the stock exchange.
	On General Gordon's Copy Of Newman's Dream Of Gerontius (1889) by William Edward Armytage Axon (Author) This book is a facsimile reprint and may contain imperfections such as marks, notations, marginalia and flawed pages.
	The Literary History of Parnell's 'Hermit' [ 1881 ] by William E. A. (William Edward Armytage) Axon (Author) Originally published in 1881. This volume from the Cornell University Library's print collections was scanned on an APT BookScan and converted to JPG 2000 format by Kirtas Technologies. All titles scanned cover to cover and pages may include marks notations and other marginalia present in the original volume.
	The Ancoats Skylark, and Other Verses: Original and Translated [ 1894 ] by William E. A. (William Edward Armytage) Axon (Author) Originally published in 1894. This volume from the Cornell University Library's print collections was scanned on an APT BookScan and converted to JPG 2000 format by Kirtas Technologies. All titles scanned cover to cover and pages may include marks notations and other marginalia present in the original volume.
	Stray Chapters in Literature, Folk-Lore, and Archaeology [ 1888 ] by William E. A. (William Edward Armytage) Axon (Author) Originally published in 1888. This volume from the Cornell University Library's print collections was scanned on an APT BookScan and converted to JPG 2000 format by Kirtas Technologies. All titles scanned cover to cover and pages may include marks notations and other marginalia present in the original volume.