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Axo-glial interactions regulate the localization of axonal paranodal proteins.

Dupree JL, Girault JA, Popko B - J. Cell Biol. (1999)

Bottom Line: Using these mutants, we have analyzed the role that axo-glial interactions play in the establishment of axonal protein distribution in the region of the node of Ranvier.Whereas the clustering of the nodal proteins, sodium channels, ankyrin(G), and neurofascin was only slightly affected, the distribution of potassium channels and paranodin, proteins that are normally concentrated in the regions juxtaposed to the node, was dramatically altered.Paranodin/contactin-associated protein (Caspr), a paranodal protein that is a potential neuronal mediator of axon-myelin binding, was not concentrated in the paranodal regions but was diffusely distributed along the internodal regions.

View Article: PubMed Central - PubMed

Affiliation: Neuroscience Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.

ABSTRACT
Mice incapable of synthesizing the abundant galactolipids of myelin exhibit disrupted paranodal axo-glial interactions in the central and peripheral nervous systems. Using these mutants, we have analyzed the role that axo-glial interactions play in the establishment of axonal protein distribution in the region of the node of Ranvier. Whereas the clustering of the nodal proteins, sodium channels, ankyrin(G), and neurofascin was only slightly affected, the distribution of potassium channels and paranodin, proteins that are normally concentrated in the regions juxtaposed to the node, was dramatically altered. The potassium channels, which are normally concentrated in the paranode/juxtaparanode, were not restricted to this region but were detected throughout the internode in the galactolipid-defi- cient mice. Paranodin/contactin-associated protein (Caspr), a paranodal protein that is a potential neuronal mediator of axon-myelin binding, was not concentrated in the paranodal regions but was diffusely distributed along the internodal regions. Collectively, these findings suggest that the myelin galactolipids are essential for the proper formation of axo-glial interactions and demonstrate that a disruption in these interactions results in profound abnormalities in the molecular organization of the paranodal axolemma.

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In the wild-type mice paranodin (green) is highly concentrated in the paranodal regions of spinal cord (a) and sciatic nerve (c) axons. In contrast, the galactolipid-deficient mice exhibit a more diffuse labeling pattern. In the mutant spinal cord (b) paranodin is evenly distributed in the axolemma throughout the internode. In the sciatic nerve (d) of these mice, paranodin is concentrated in the paranode but the interface between the paranode and the juxtaparanode is not clearly demarcated. a and b, eight images 0.26 μm apart; double-labeled for paranodin in green and phosphorylated neurofilament in red. c and d, eight images 0.4 μm apart; double-labeled for paranodin in green and myelin basic protein in red. Bar, 5 μm.
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Figure 2: In the wild-type mice paranodin (green) is highly concentrated in the paranodal regions of spinal cord (a) and sciatic nerve (c) axons. In contrast, the galactolipid-deficient mice exhibit a more diffuse labeling pattern. In the mutant spinal cord (b) paranodin is evenly distributed in the axolemma throughout the internode. In the sciatic nerve (d) of these mice, paranodin is concentrated in the paranode but the interface between the paranode and the juxtaparanode is not clearly demarcated. a and b, eight images 0.26 μm apart; double-labeled for paranodin in green and phosphorylated neurofilament in red. c and d, eight images 0.4 μm apart; double-labeled for paranodin in green and myelin basic protein in red. Bar, 5 μm.

Mentions: The structural abnormalities at the node of the galactolipid-deficient mice appear to be related to compromised axo-glial interactions, such that we have analyzed the distribution of two potential neuronal adhesion molecules: paranodin and neurofascin. In addition, we have determined the distribution of the cytoskeleton-associated molecule ankyrinG. Using a combination of immunocytochemical techniques and confocal microscopy, we demonstrated the complete absence of paranodin accumulation in the paranodal regions of the myelinated fibers of the spinal cord in the CGT−/− mouse (Fig. 2, a and b). In the galactolipid mutants, paranodin appeared to be diffusely distributed along the axon (Fig. 2c and Fig. d), resembling the expression pattern of unmyelinated fibers (Einheber et al. 1997). In the sciatic nerve, paranodin was localized to the paranodal region; however, the staining intensity was reduced and the border between the paranode and the juxtaparanode was not as clearly defined as in the wild-type sciatic nerve (Fig. 2c and Fig. d). Paranodin was not detected in the paranode of any of the CNS fibers examined and reduced accumulations of paranodin were always observed in the paranode of the PNS fibers observed. Western blot analysis revealed no difference in the level of paranodin expression between the galactolipid mutant and wild-type animals for either the spinal cord or the sciatic nerve (Fig. 3), indicating that the diminished immunoreactivity was a result of abnormal paranodal accumulations. In contrast, the distribution of the nodal proteins neurofascin (Fig. 4) and ankyrinG (data not shown) did not appear altered in either the spinal cord or the sciatic nerve of the mutant.


Axo-glial interactions regulate the localization of axonal paranodal proteins.

Dupree JL, Girault JA, Popko B - J. Cell Biol. (1999)

In the wild-type mice paranodin (green) is highly concentrated in the paranodal regions of spinal cord (a) and sciatic nerve (c) axons. In contrast, the galactolipid-deficient mice exhibit a more diffuse labeling pattern. In the mutant spinal cord (b) paranodin is evenly distributed in the axolemma throughout the internode. In the sciatic nerve (d) of these mice, paranodin is concentrated in the paranode but the interface between the paranode and the juxtaparanode is not clearly demarcated. a and b, eight images 0.26 μm apart; double-labeled for paranodin in green and phosphorylated neurofilament in red. c and d, eight images 0.4 μm apart; double-labeled for paranodin in green and myelin basic protein in red. Bar, 5 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2168103&req=5

Figure 2: In the wild-type mice paranodin (green) is highly concentrated in the paranodal regions of spinal cord (a) and sciatic nerve (c) axons. In contrast, the galactolipid-deficient mice exhibit a more diffuse labeling pattern. In the mutant spinal cord (b) paranodin is evenly distributed in the axolemma throughout the internode. In the sciatic nerve (d) of these mice, paranodin is concentrated in the paranode but the interface between the paranode and the juxtaparanode is not clearly demarcated. a and b, eight images 0.26 μm apart; double-labeled for paranodin in green and phosphorylated neurofilament in red. c and d, eight images 0.4 μm apart; double-labeled for paranodin in green and myelin basic protein in red. Bar, 5 μm.
Mentions: The structural abnormalities at the node of the galactolipid-deficient mice appear to be related to compromised axo-glial interactions, such that we have analyzed the distribution of two potential neuronal adhesion molecules: paranodin and neurofascin. In addition, we have determined the distribution of the cytoskeleton-associated molecule ankyrinG. Using a combination of immunocytochemical techniques and confocal microscopy, we demonstrated the complete absence of paranodin accumulation in the paranodal regions of the myelinated fibers of the spinal cord in the CGT−/− mouse (Fig. 2, a and b). In the galactolipid mutants, paranodin appeared to be diffusely distributed along the axon (Fig. 2c and Fig. d), resembling the expression pattern of unmyelinated fibers (Einheber et al. 1997). In the sciatic nerve, paranodin was localized to the paranodal region; however, the staining intensity was reduced and the border between the paranode and the juxtaparanode was not as clearly defined as in the wild-type sciatic nerve (Fig. 2c and Fig. d). Paranodin was not detected in the paranode of any of the CNS fibers examined and reduced accumulations of paranodin were always observed in the paranode of the PNS fibers observed. Western blot analysis revealed no difference in the level of paranodin expression between the galactolipid mutant and wild-type animals for either the spinal cord or the sciatic nerve (Fig. 3), indicating that the diminished immunoreactivity was a result of abnormal paranodal accumulations. In contrast, the distribution of the nodal proteins neurofascin (Fig. 4) and ankyrinG (data not shown) did not appear altered in either the spinal cord or the sciatic nerve of the mutant.

Bottom Line: Using these mutants, we have analyzed the role that axo-glial interactions play in the establishment of axonal protein distribution in the region of the node of Ranvier.Whereas the clustering of the nodal proteins, sodium channels, ankyrin(G), and neurofascin was only slightly affected, the distribution of potassium channels and paranodin, proteins that are normally concentrated in the regions juxtaposed to the node, was dramatically altered.Paranodin/contactin-associated protein (Caspr), a paranodal protein that is a potential neuronal mediator of axon-myelin binding, was not concentrated in the paranodal regions but was diffusely distributed along the internodal regions.

View Article: PubMed Central - PubMed

Affiliation: Neuroscience Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.

ABSTRACT
Mice incapable of synthesizing the abundant galactolipids of myelin exhibit disrupted paranodal axo-glial interactions in the central and peripheral nervous systems. Using these mutants, we have analyzed the role that axo-glial interactions play in the establishment of axonal protein distribution in the region of the node of Ranvier. Whereas the clustering of the nodal proteins, sodium channels, ankyrin(G), and neurofascin was only slightly affected, the distribution of potassium channels and paranodin, proteins that are normally concentrated in the regions juxtaposed to the node, was dramatically altered. The potassium channels, which are normally concentrated in the paranode/juxtaparanode, were not restricted to this region but were detected throughout the internode in the galactolipid-defi- cient mice. Paranodin/contactin-associated protein (Caspr), a paranodal protein that is a potential neuronal mediator of axon-myelin binding, was not concentrated in the paranodal regions but was diffusely distributed along the internodal regions. Collectively, these findings suggest that the myelin galactolipids are essential for the proper formation of axo-glial interactions and demonstrate that a disruption in these interactions results in profound abnormalities in the molecular organization of the paranodal axolemma.

Show MeSH
Related in: MedlinePlus