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Polarity orientation of axonal microtubules
Abstract:
The polarity orientation of cellular microtubules is widely regarded to be important in understanding the control of microtubule assembly and microtubule-based motility in vivo. We have used a modification of the method of Heidemann and McIntosh (Nature (Lond.). 286:517-519) to determine the polarity orientation of axonal microtubules in postganglionic sympathetic fibers of the cat. In fibers from three cats we were able to visualize the polarity of 68% of the axonal microtubules; of these, 96% showed the same polarity orientation. Our interpretation is that the rapidly growing end of all axonal microtubules is distal to the cell body. We support Kirschner's hypothesis on microtubule organizing centers. (J. Cell Biol. 86:330-334), although this interpretation raises questions about the continuity of axonal microtubules. Our results are inconsistent with a number of models for axonal transport based on force production on the surface of microtubules in which the direction of force is determined by the polarity of microtubules.
Insights
This study determined the polarity orientation of axonal microtubules in cats, finding that most microtubules grow away from the cell body. This supports microtubule organizing center hypotheses but challenges some axonal transport models.
Area of Science:
- Cell Biology
- Neuroscience
- Cytoskeleton Dynamics
Background:
- Microtubule polarity is crucial for cellular functions like assembly and motility.
- Understanding microtubule orientation in neurons is key to explaining axonal transport.
Purpose of the Study:
- To determine the polarity orientation of axonal microtubules in postganglionic sympathetic fibers.
- To investigate the implications of microtubule polarity for axonal transport models.
Main Methods:
- A modified Heidemann and McIntosh method was employed.
- Microtubule polarity was visualized in axonal fibers from cat subjects.
Main Results:
- The polarity of 68% of axonal microtubules was determined.
- A consistent polarity orientation was observed in 96% of visualized microtubules.
- The rapidly growing end of axonal microtubules was found to be distal to the cell body.
Conclusions:
- Results support Kirschner's hypothesis on microtubule organizing centers.
- The findings raise questions regarding the continuity of axonal microtubules.
- The data contradict models of axonal transport dependent on microtubule surface force production.