The neuronal adhesion protein TAG-1 is expressed by Schwann cells and oligodendrocytes and is localized to the juxtaparanodal region of myelinated fibers - PubMed (original) (raw)

The neuronal adhesion protein TAG-1 is expressed by Schwann cells and oligodendrocytes and is localized to the juxtaparanodal region of myelinated fibers

Maria Traka et al. J Neurosci. 2002.

Abstract

The neural cell adhesion molecule TAG-1, which is a glycosylphosphatidylinositol-linked member of the Ig superfamily, is expressed by various neuronal populations in the developing CNS and PNS. We demonstrate here that Schwann cells and oligodendrocytes also express TAG-1. In the PNS, TAG-1 is detected in ensheathing Schwann cells early postnatally and is maintained throughout adulthood. In mature myelinated fibers of the CNS and PNS, TAG-1 is localized to the juxtaparanodal region. The CNS of the UDP-galactose ceramide galactosyl transferase(-/-) (CGT(-/-)) mouse mutants, which do not synthesize the abundant galactolipids of myelin, display severely disrupted axoglial interactions at the paranodal region. In contrast, axoglial interactions in the PNS of these mutants are less affected. Interestingly, TAG-1 localization is completely undetected in myelinated fibers of the CNS. In the PNS of these mutants, TAG-1 abnormally localizes in the paranodal region. These data raise the intriguing possibility that TAG-1 localization in the juxtaparanodal area mediates, or at least requires, the axoglial contact normally displayed in this region. The abnormal localization of TAG-1 in the CGT mutants might contribute to the disrupted axoglial interactions observed in these animals.

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Figures

Fig. 1.

TAG-1 is expressed by Schwann cells during development and in the adult. A, In longitudinal sections from adult sciatic nerve, TAG-1 mRNA is detected in cells with the typical spindle shape morphology of Schwann cells (higher magnification, B). C, Western blot analysis shows that TAG-1 is expressed in whole protein extracts from P5 sciatic nerve (lane 1, 30 μg) as a 135 kDa band. Protein extract from postnatal cerebellum was loaded in lane 2 (10 μg). D, A rat TAG-1-specific 524 bp band is detected by reverse transcription-PCR analysis in total RNA isolated from Schwann cells after 4 DIV (lane 1), P5 sciatic nerve (lane 2), adult sciatic nerve (lane 3), and postnatal cerebellum (lane 4). A cyclophilin 400 bp band was used to normalize the mRNA levels in each sample. E, The gel in D was hybridized with a 2.5 kb 32P-labeled_Kpn_I–_Kpn_I DNA fragment of TAG-564 plasmid (Furley et al., 1990). Scale bars: A, 10 μm;B, 5 μm.

Fig. 2.

TAG-1 is expressed in Schwann cells in vitro. A, Schwann cell cultures, derived from P5 sciatic nerve, express TAG-1 on their surface in a punctate pattern, after 4 DIV. C, At this time point almost all the cells express the Ca2+-binding protein S-100, NCAM on their surface (E), and GFAP intracellularly (G) . B, D,F, and H are the phase-contrast optics of_A_, C, E, and_G_. Scale bar, 25 μm.

Fig. 3.

Distribution of TAG-1 in Schwann cells of postnatal sciatic nerve. A, On P6 sciatic nerve sections, TAG-1 is expressed by ensheathing Schwann cells detected by L1 labeling (B, green). _C_is the combined image of A and B that shows that both channels overlap (yellow).D, On P6 sciatic nerve sections, myelinating Schwann cells detected by MAG labeling (green) are negative for TAG-1 (red), which appears in ensheathing Schwann cells only. E, At P6 myelinated fibers, TAG-1 (red) does not appear to be clustered, whereas in the paranodal region paranodin/Caspr is already detected (green). A–C, Eleven images, 0.6 μm apart; D, nine images, 0.9 μm apart;E, seven images, 0.6 μm apart. Scale bar, 10 μm.

Fig. 4.

TAG-1 is expressed in the juxtaparanodal region of PNS myelinated fibers in the adult. A, In adult sciatic nerve, TAG-1 continues to be expressed in ensheathing Schwann cells, but it is also detected in myelinated fibers in the region, probably corresponding to the juxtaparanode (arrows).B, TAG-1 is expressed in an ensheathing Schwann cell detected by L1 labeling (C). D is the combined image of B and C, which shows that both channels overlap (yellow).E, TAG-1 is also detected in Schmidt-Lanterman incisures (arrows) of myelinated fibers. The juxtaparanodal localization of TAG-1 (F, G, red) in adult sciatic nerve was confirmed by double labeling for MAG (G, green), which is localized in the paranodal loops of adult myelinated fibers. TAG-1 (arrowheads) appears to be localized adjacent to the paranodal region indicated by MAG labeling (arrows).H, In the internode, TAG-1 (red, arrows) is in register with MAG staining in the incisures (green), which is closest to the axon.A, Nine images, 0.9 μm apart; B–D, six images, 0.7 μm apart; E, eight images, 0.8 μm apart;F, G, six images, 0.85 μm apart;H, five images, 1 μm apart. Scale bars:A, 20 μm; B–H, 10 μm.

Fig. 5.

TAG-1 is colocalized with Kv1.1 potassium channels in the PNS myelinated fibers. In teased nerve fibers of adult sciatic nerve, TAG-1 (A, C, red) appears to be colocalized with the Kv1.1 potassium channels (B, C, green) in myelinated fibers at the juxtaparanodal region (large arrowheads), at the incisures (arrows), and at the inner mesaxon (small arrowheads) because both channels overlap (C, yellow). At the juxtaparanode, TAG-1 (D, F, red) colocalization with Kv1.1 potassium channels (E, F, green) is shown in a higher magnification in F(yellow). Cross-sectional slices through the image volume showing TAG-1/Kv1.1 overlap were performed in the_xz_ (G) and yz plane (H) in the regions shown by numbers. TAG-1 (red) and Kv1.1 potassium channels (green) may be localized in different membranes in the juxtaparanodal region because there is a limited overlap of the two channels in the xz slices (G1–G3) and yz slices (H1–H3) acquired.I, The planes of the xz and_yz_ slices according to the image sections are demonstrated. A–C, Four images, 1 μm apart;D–H, seven images, 0.4 μm apart. Scale bar, 10 μm.

Fig. 6.

TAG-1 is expressed by oligodendrocytes and accumulates at the juxtaparanodal region. A, In adult spinal cord sections, TAG-1 mRNA is expressed in small cells of the white matter (arrows, higher magnification in_B_). In the ventral horn TAG-1 is also detected in large, spindle-shaped neurons (arrowheads, higher magnification in B). C, In the white matter of adult spinal cord sections, TAG-1 protein is present in the soma of round to oval cells (green, arrows). D, In these cells, TAG-1 (green) colocalizes with APC (red), a marker for oligodendrocytes, as both channels overlap (yellow, arrows). E, TAG-1 also appears in clusters in white matter (red, arrows).F, Sequential labeling for paranodin/Caspr (green) shows that TAG-1 (red) has a discrete distribution and is concentrated in the juxtaparanode of myelinated fibers. G, TAG-1 protein is detected in myelin-rich membrane fractions isolated from adult spinal cord as a 135 kDa band and a 90 kDa adult isoform (lane 1). Whole protein extract from postnatal cerebellum was loaded in lane 2. Low levels of L1 protein are detected in the above myelin fractions (180 kDa band, lane 3). In these fractions, MBP (18.5 kDa band, lane 4) is abundantly expressed because it is detected in 130 of the amount loaded in_lanes 1_ and 3. C, Ten images, 0.4 μm apart; D, 5 images, 0.4 μm apart; E, F, 11 images, 0.9 μm apart. Scale bars: A, C, D, 20 μm; B, E, F, 5 μm.

Fig. 7.

Distribution of TAG-1 in myelinated fibers of CGT-deficient mice. In wild-type sciatic nerve, TAG-1 (A, B, red) and Kv1.1 potassium channels (B, green) are colocalized in the juxtaparanodal region of myelinated fibers (B, yellow). In galactolipid-deficient mice, TAG-1 (C, D, red) is detected in the paranodal region similar to Kv1.1 potassium channels (D, green) because both channels overlap in this area (D, yellow). In the_inset_ of D the colocalization TAG-1 with Kv1.1 potassium channels is shown in a higher magnification.E, In the CNS of wild-type animals, TAG-1 (green) is clustered in the juxtaparanodal area of myelinated fibers in spinal cord, in contrast to paranodin/Caspr (red), which is localized in the paranode.F, In galactolipid-deficient CNS TAG-1 (green) is reduced to undetectable levels, whereas paranodin/Caspr (red) appears diffuse throughout the internodal axolemma. A, B, Six images, 0.8 μm apart; C, D, 7 images, 0.7 μm apart; E, 22 images, 0.4 μm apart;F, 14 images, 0.4 μm apart. Scale bars, 10 μm.

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The neuronal adhesion protein TAG-1 is expressed by Schwann cells and oligodendrocytes and is localized to the juxtaparanodal region of myelinated fibers - PubMed (original) (raw)