Johns Hopkins study finds axons form repeating nanoscale pearls, not smooth tubes
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Researchers at Johns Hopkins Medicine found that some axons in mouse neurons form repeating nanoscale swellings called non-synaptic varicosities, challenging the textbook view of axons as smooth tubes. The study was published online in Nature Neuroscience on December 2, 2024. Related research has since documented pearled axons in human brain tissue.
Key Facts
- The study was published online in Nature Neuroscience on December 2, 2024.
- Researchers at Johns Hopkins Medicine worked with mouse neurons and found repeating nanoscale swellings called non-synaptic varicosities.
- Related research has since documented pearled axons in human brain tissue.
- Shigeki Watanabe, Ph.D., is an associate professor of cell biology and neuroscience at the Johns Hopkins University School of Medicine.
- A Harvard University team reported repeating skeletal components within axons in a study published in 2012.
Axon Structure
Axons are the long extensions that allow neurons to transmit electrical signals to other cells. The conventional illustration shows a relatively uniform tube interrupted by occasional bulges called synaptic varicosities that hold neurotransmitters. Beaded axons have long been observed in dying neurons and in neurodegenerative conditions, including Parkinson's disease. In those settings, the beading can accompany damage to the cell membrane and the internal framework that helps maintain the axon's structure.
Non-Synaptic Varicosities
The Johns Hopkins study found much smaller, repeating swellings in axons examined under conditions intended to preserve their normal structure. The researchers called these regions non-synaptic varicosities, and unlike the familiar bulges associated with communication sites, these swellings were not synapses. The study did not suggest that every beaded axon is damaged; instead, it pointed to a form of nanoscale pearling that may be part of the normal architecture of the axons studied.
Research Origins
Shigeki Watanabe's interest began with observations of repeating pearls along axons in worms. A conversation with Swiss scientist Graham Knott, Ph.D., prompted him to investigate further. One possible explanation involved the axon's internal skeleton, a supporting network of proteins. A Harvard University team had reported repeating skeletal components within axons in a study published in 2012. Watanabe and Knott wondered whether disrupting that framework would make the pearls disappear.
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