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What makes an axon an axon?
November 10, 2008Inside 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
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
Axon Current Events and Axon News RSSFindings show nanomedicine promising for treating spinal cord injuries
Researchers at Purdue University have discovered a new approach for repairing damaged nerve fibers in spinal cord injuries using nano-spheres that could be injected into the blood shortly after an accident.
Master regulator found for regenerating nerve fibers in live animals
Researchers at Children's Hospital Boston report that an enzyme known as Mst3b, previously identified in their lab, is essential for regenerating damaged axons (nerve fibers) in a live animal model, in both the peripheral and central nervous systems.
Rethinking Alzheimer's disease and its treatment targets
The standard explanation for what causes Alzheimer's is known as the amyloid hypothesis, which posits that the disease results from of an accumulation of the peptide amyloid beta, the toxic protein fragments that deposit in the brain and become the sticky plaques that have defined Alzheimer's for more than 100 years.
MDC researchers discover molecule responsible for axonal branching
The human brain consists of about 100 billion (1011) neurons, which altogether form about 100 trillion (1014) synaptic connections with each other.
Neurons found to be similar to Electoral College
A tiny neuron is a very complicated structure. Its complex network of dendrites, axons and synapses is constantly dealing with information, deciding whether or not to send a nerve impulse, to drive a certain action.
Finding the right connection after spinal cord injury
In a major step in spinal cord injury research, scientists at the University of California, San Diego School of Medicine have demonstrated that regenerating axons can be guided to their correct targets and re-form connections after spinal cord injury.
Huntington's disease deciphered
Researchers at the University of Illinois at Chicago College of Medicine have discovered how the mutated huntingtin gene acts on the nervous system to create the devastation of Huntington's disease.
Protein regulates movement of mitochondria in brain cells
Scientists have identified a protein in the brain that plays a key role in the function of mitochondria - the part of the cell that supplies energy, supports cellular activity, and potentially wards off threats from disease.
Identification of a key molecular pathway required for brain neural circuit formation
The research group of Dr. Frédéric Charron, a researcher at the Institut de recherches cliniques de Montréal (IRCM), has made a discovery which could help treat spinal cord injuries and neurodegenerative diseases.
Mechanism of Alzheimer's suggests combination therapy needed
Researchers at the University of Illinois at Chicago College of Medicine have discovered a mode of action for mysterious but diagnostic protein snarls found in the brains of Alzheimer's patients that suggests a one-two punch of therapy may be needed to combat the neurodegenerative disease.
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