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Heterophilic binding of L1 on unmyelinated sensory axons mediates Schwann cell adhesion and is required for axonal survival.

Haney CA, Sahenk Z, Li C, Lemmon VP, Roder J, Trapp BD - J. Cell Biol. (1999)

Bottom Line: We demonstrate that L1 is present on axons and Schwann cells of sensory unmyelinated fibers, but only on Schwann cells of sympathetic unmyelinated fibers.In L1-deficient sensory nerves, Schwann cells formed but failed to retain normal axonal ensheathment.In nerve transplant studies, loss of axonal-L1, but not Schwann cell-L1, reproduced the L1-deficient phenotype.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA.

ABSTRACT
This study investigated the function of the adhesion molecule L1 in unmyelinated fibers of the peripheral nervous system (PNS) by analysis of L1- deficient mice. We demonstrate that L1 is present on axons and Schwann cells of sensory unmyelinated fibers, but only on Schwann cells of sympathetic unmyelinated fibers. In L1-deficient sensory nerves, Schwann cells formed but failed to retain normal axonal ensheathment. L1-deficient mice had reduced sensory function and loss of unmyelinated axons, while sympathetic unmyelinated axons appeared normal. In nerve transplant studies, loss of axonal-L1, but not Schwann cell-L1, reproduced the L1-deficient phenotype. These data establish that heterophilic axonal-L1 interactions mediate adhesion between unmyelinated sensory axons and Schwann cells, stabilize the polarization of Schwann cell surface membranes, and mediate a trophic effect that assures axonal survival.

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L1 and MAG gene expression in transgenic mice. (A) Southern blot analysis of MAG and L1-deficient mice. The L1 probe (upper panel) detected an 11-kb fragment in wild-type (wt) and MAG-deficient (MAG−/−) mice, and an 8-kb fragment in L1-deficient (L1 −/y) and L1/MAG-deficient (LMko) mice, (EcoR1 cut). The MAG probe (lower panel) detected a 7.5- and a 4.5-kb fragment in wild-type and L1-deficient mice, and a 5.5- and a 4.5-kb fragment in MAG- and L1/MAG-deficient mice (BamHI-HindIII cut). L1 heterozygous (L1 −/x)/MAG-deficient (−/−) females were used as breeders for the L1/MAG-deficient line and showed an 11- and 8-kb band when probed for L1, and a 5.5- and 4.5-kb band when probed for MAG. (B) Western blot analysis of CNS and PNS protein extracts from wild-type, MAG-deficient, L1-deficient, and MAG/L1-deficient mice. MAG antibodies detected a 100-kD band in wild-type and L1-deficient mice. MAG immunoreactivity was not detected in MAG- or L1/MAG-deficient mice. L1 antibodies detected a 200-kD band in wild-type and MAG-deficient mice. L1 immunoreactivity was not detected in L1- or L1/MAG-deficient mice.
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Figure 1: L1 and MAG gene expression in transgenic mice. (A) Southern blot analysis of MAG and L1-deficient mice. The L1 probe (upper panel) detected an 11-kb fragment in wild-type (wt) and MAG-deficient (MAG−/−) mice, and an 8-kb fragment in L1-deficient (L1 −/y) and L1/MAG-deficient (LMko) mice, (EcoR1 cut). The MAG probe (lower panel) detected a 7.5- and a 4.5-kb fragment in wild-type and L1-deficient mice, and a 5.5- and a 4.5-kb fragment in MAG- and L1/MAG-deficient mice (BamHI-HindIII cut). L1 heterozygous (L1 −/x)/MAG-deficient (−/−) females were used as breeders for the L1/MAG-deficient line and showed an 11- and 8-kb band when probed for L1, and a 5.5- and 4.5-kb band when probed for MAG. (B) Western blot analysis of CNS and PNS protein extracts from wild-type, MAG-deficient, L1-deficient, and MAG/L1-deficient mice. MAG antibodies detected a 100-kD band in wild-type and L1-deficient mice. MAG immunoreactivity was not detected in MAG- or L1/MAG-deficient mice. L1 antibodies detected a 200-kD band in wild-type and MAG-deficient mice. L1 immunoreactivity was not detected in L1- or L1/MAG-deficient mice.

Mentions: Mice deficient for both MAG and L1 were generated by initially breeding SV-129 L1 heterozygote females (−x/+x) with 129 × CD1 MAG-deficient (−/−) males. From these breedings, female L1 heterozygotes (−x/+x)/MAG heterozygotes (+/−) were identified and bred to MAG-deficient (−/−) males. Female L1 heterozygotes (−x/+x)/MAG-deficient (−/−) mice were identified and bred with MAG-deficient males to produce L1/MAG-deficient males (−x / y for the L1 gene and −/− for the MAG gene). MAG-deficient, L1-deficient, and L1/MAG-deficient mice were identified in Southern blots probed with MAG and L1 cDNAs (Fig. 1 A). When probed with the L1 cDNA, wild-type and MAG-deficient DNA (digested with EcoR1) contained an 11-kb band while DNA from L1-deficient and L1/MAG-deficient males contained a band at 8 kb. L1 heterozygote females had bands at both 11 and 8 kb. Wild-type and L1-deficient DNA (digested with BamHI and HindIII) contained two MAG bands (7.5 and 4.5 kb). The MAG-deficient and L1/MAG-deficient mice showed a diagnostic 5.5-kb band as well as the 4.5-kb band. DNA from L1 heterozygote/MAG-deficient females also contained bands at 5.5 and 4.5 kb. The absence of L1 and MAG protein in the respective mice was confirmed by Western blot analysis of CNS and PNS protein extracts (Fig. 1 B). MAG antibodies detected an appropriate band at 100 kD only in wild-type and L1-deficient mice. L1 antibodies detected a band of ∼200 kD only in wild-type and MAG-deficient mice. A large percentage of the L1-deficient and L1/MAG-deficient males were runted from birth and remained smaller than the male littermates until approximately one month of age.


Heterophilic binding of L1 on unmyelinated sensory axons mediates Schwann cell adhesion and is required for axonal survival.

Haney CA, Sahenk Z, Li C, Lemmon VP, Roder J, Trapp BD - J. Cell Biol. (1999)

L1 and MAG gene expression in transgenic mice. (A) Southern blot analysis of MAG and L1-deficient mice. The L1 probe (upper panel) detected an 11-kb fragment in wild-type (wt) and MAG-deficient (MAG−/−) mice, and an 8-kb fragment in L1-deficient (L1 −/y) and L1/MAG-deficient (LMko) mice, (EcoR1 cut). The MAG probe (lower panel) detected a 7.5- and a 4.5-kb fragment in wild-type and L1-deficient mice, and a 5.5- and a 4.5-kb fragment in MAG- and L1/MAG-deficient mice (BamHI-HindIII cut). L1 heterozygous (L1 −/x)/MAG-deficient (−/−) females were used as breeders for the L1/MAG-deficient line and showed an 11- and 8-kb band when probed for L1, and a 5.5- and 4.5-kb band when probed for MAG. (B) Western blot analysis of CNS and PNS protein extracts from wild-type, MAG-deficient, L1-deficient, and MAG/L1-deficient mice. MAG antibodies detected a 100-kD band in wild-type and L1-deficient mice. MAG immunoreactivity was not detected in MAG- or L1/MAG-deficient mice. L1 antibodies detected a 200-kD band in wild-type and MAG-deficient mice. L1 immunoreactivity was not detected in L1- or L1/MAG-deficient mice.
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Related In: Results  -  Collection

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Figure 1: L1 and MAG gene expression in transgenic mice. (A) Southern blot analysis of MAG and L1-deficient mice. The L1 probe (upper panel) detected an 11-kb fragment in wild-type (wt) and MAG-deficient (MAG−/−) mice, and an 8-kb fragment in L1-deficient (L1 −/y) and L1/MAG-deficient (LMko) mice, (EcoR1 cut). The MAG probe (lower panel) detected a 7.5- and a 4.5-kb fragment in wild-type and L1-deficient mice, and a 5.5- and a 4.5-kb fragment in MAG- and L1/MAG-deficient mice (BamHI-HindIII cut). L1 heterozygous (L1 −/x)/MAG-deficient (−/−) females were used as breeders for the L1/MAG-deficient line and showed an 11- and 8-kb band when probed for L1, and a 5.5- and 4.5-kb band when probed for MAG. (B) Western blot analysis of CNS and PNS protein extracts from wild-type, MAG-deficient, L1-deficient, and MAG/L1-deficient mice. MAG antibodies detected a 100-kD band in wild-type and L1-deficient mice. MAG immunoreactivity was not detected in MAG- or L1/MAG-deficient mice. L1 antibodies detected a 200-kD band in wild-type and MAG-deficient mice. L1 immunoreactivity was not detected in L1- or L1/MAG-deficient mice.
Mentions: Mice deficient for both MAG and L1 were generated by initially breeding SV-129 L1 heterozygote females (−x/+x) with 129 × CD1 MAG-deficient (−/−) males. From these breedings, female L1 heterozygotes (−x/+x)/MAG heterozygotes (+/−) were identified and bred to MAG-deficient (−/−) males. Female L1 heterozygotes (−x/+x)/MAG-deficient (−/−) mice were identified and bred with MAG-deficient males to produce L1/MAG-deficient males (−x / y for the L1 gene and −/− for the MAG gene). MAG-deficient, L1-deficient, and L1/MAG-deficient mice were identified in Southern blots probed with MAG and L1 cDNAs (Fig. 1 A). When probed with the L1 cDNA, wild-type and MAG-deficient DNA (digested with EcoR1) contained an 11-kb band while DNA from L1-deficient and L1/MAG-deficient males contained a band at 8 kb. L1 heterozygote females had bands at both 11 and 8 kb. Wild-type and L1-deficient DNA (digested with BamHI and HindIII) contained two MAG bands (7.5 and 4.5 kb). The MAG-deficient and L1/MAG-deficient mice showed a diagnostic 5.5-kb band as well as the 4.5-kb band. DNA from L1 heterozygote/MAG-deficient females also contained bands at 5.5 and 4.5 kb. The absence of L1 and MAG protein in the respective mice was confirmed by Western blot analysis of CNS and PNS protein extracts (Fig. 1 B). MAG antibodies detected an appropriate band at 100 kD only in wild-type and L1-deficient mice. L1 antibodies detected a band of ∼200 kD only in wild-type and MAG-deficient mice. A large percentage of the L1-deficient and L1/MAG-deficient males were runted from birth and remained smaller than the male littermates until approximately one month of age.

Bottom Line: We demonstrate that L1 is present on axons and Schwann cells of sensory unmyelinated fibers, but only on Schwann cells of sympathetic unmyelinated fibers.In L1-deficient sensory nerves, Schwann cells formed but failed to retain normal axonal ensheathment.In nerve transplant studies, loss of axonal-L1, but not Schwann cell-L1, reproduced the L1-deficient phenotype.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA.

ABSTRACT
This study investigated the function of the adhesion molecule L1 in unmyelinated fibers of the peripheral nervous system (PNS) by analysis of L1- deficient mice. We demonstrate that L1 is present on axons and Schwann cells of sensory unmyelinated fibers, but only on Schwann cells of sympathetic unmyelinated fibers. In L1-deficient sensory nerves, Schwann cells formed but failed to retain normal axonal ensheathment. L1-deficient mice had reduced sensory function and loss of unmyelinated axons, while sympathetic unmyelinated axons appeared normal. In nerve transplant studies, loss of axonal-L1, but not Schwann cell-L1, reproduced the L1-deficient phenotype. These data establish that heterophilic axonal-L1 interactions mediate adhesion between unmyelinated sensory axons and Schwann cells, stabilize the polarization of Schwann cell surface membranes, and mediate a trophic effect that assures axonal survival.

Show MeSH
Related in: MedlinePlus