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A synaptic nidogen: developmental regulation and role of nidogen-2 at the neuromuscular junction.

Fox MA, Ho MS, Smyth N, Sanes JR - Neural Dev (2008)

Bottom Line: All four core components of the basal lamina have synaptically enriched isoforms.Together, they form a highly specialized synaptic cleft material.Individually, they play distinct roles in the formation, maturation and maintenance of the neuromuscular junction.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Molecular and Cellular Biology and Center for Brain Science, Harvard University, Cambridge, MA 02138, USA. mafox@vcu.edu

ABSTRACT

Background: The skeletal neuromuscular junction is a useful model for elucidating mechanisms that regulate synaptogenesis. Developmentally important intercellular interactions at the neuromuscular junction are mediated by the synaptic portion of a basal lamina that completely ensheaths each muscle fiber. Basal laminas in general are composed of four main types of glycosylated proteins: laminins, collagens IV, heparan sulfate proteoglycans and nidogens (entactins). The portion of the muscle fiber basal lamina that passes between the motor nerve terminal and postsynaptic membrane has been shown to bear distinct isoforms of the first three of these. For laminins and collagens IV, the proteins are deposited by the muscle; a synaptic proteoglycan, z-agrin, is deposited by the nerve. In each case, the synaptic isoform plays key roles in organizing the neuromuscular junction. Here, we analyze the fourth family, composed of nidogen-1 and -2.

Results: In adult muscle, nidogen-1 is present throughout muscle fiber basal lamina, while nidogen-2 is concentrated at synapses. Nidogen-2 is initially present throughout muscle basal lamina, but is lost from extrasynaptic regions during the first three postnatal weeks. Neuromuscular junctions in mutant mice lacking nidogen-2 appear normal at birth, but become topologically abnormal as they mature. Synaptic laminins, collagens IV and heparan sulfate proteoglycans persist in the absence of nidogen-2, suggesting the phenotype is not secondary to a general defect in the integrity of synaptic basal lamina. Further genetic studies suggest that synaptic localization of each of the four families of synaptic basal lamina components is independent of the other three.

Conclusion: All four core components of the basal lamina have synaptically enriched isoforms. Together, they form a highly specialized synaptic cleft material. Individually, they play distinct roles in the formation, maturation and maintenance of the neuromuscular junction.

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Nidogen-2 localized to synaptic sites in the absence of other synaptic basal lamina components. (A-E) Nidogen-2 was properly localized at synaptic sites (labeled with α-bungarotoxin (BTX)) in mutant mice lacking laminin α4 (lama4-/-) (A), laminin α5 (lama5M/M:HSA-Cre) (B), both laminin α4 and α5 (lama4-/-; lama5M/M:HSA-Cre) (C), laminin β2 (lamb2-/-) (D) and all four synaptic collagen IV chains (col4a5-/Y) (E). Scale bar is 5 μm.
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Figure 9: Nidogen-2 localized to synaptic sites in the absence of other synaptic basal lamina components. (A-E) Nidogen-2 was properly localized at synaptic sites (labeled with α-bungarotoxin (BTX)) in mutant mice lacking laminin α4 (lama4-/-) (A), laminin α5 (lama5M/M:HSA-Cre) (B), both laminin α4 and α5 (lama4-/-; lama5M/M:HSA-Cre) (C), laminin β2 (lamb2-/-) (D) and all four synaptic collagen IV chains (col4a5-/Y) (E). Scale bar is 5 μm.

Mentions: Fragmentation and immaturity similar to that observed in nidogen-2 mutants has been reported in collagen α5(IV) and laminin α4 mutants and in laminin α4/α5 double mutants, respectively [12,18,19]. However, nidogen-2 remained concentrated in the synaptic BL of NMJs in all of these mutants (Figure 9). Thus, synaptic laminins and collagens IV are dispensable for concentrating nidogen-2 in the synaptic cleft. Moreover, the absence of nidogen-2 is not responsible for fragmentation of synapses lacking synaptic laminins or collagens IV.


A synaptic nidogen: developmental regulation and role of nidogen-2 at the neuromuscular junction.

Fox MA, Ho MS, Smyth N, Sanes JR - Neural Dev (2008)

Nidogen-2 localized to synaptic sites in the absence of other synaptic basal lamina components. (A-E) Nidogen-2 was properly localized at synaptic sites (labeled with α-bungarotoxin (BTX)) in mutant mice lacking laminin α4 (lama4-/-) (A), laminin α5 (lama5M/M:HSA-Cre) (B), both laminin α4 and α5 (lama4-/-; lama5M/M:HSA-Cre) (C), laminin β2 (lamb2-/-) (D) and all four synaptic collagen IV chains (col4a5-/Y) (E). Scale bar is 5 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2567315&req=5

Figure 9: Nidogen-2 localized to synaptic sites in the absence of other synaptic basal lamina components. (A-E) Nidogen-2 was properly localized at synaptic sites (labeled with α-bungarotoxin (BTX)) in mutant mice lacking laminin α4 (lama4-/-) (A), laminin α5 (lama5M/M:HSA-Cre) (B), both laminin α4 and α5 (lama4-/-; lama5M/M:HSA-Cre) (C), laminin β2 (lamb2-/-) (D) and all four synaptic collagen IV chains (col4a5-/Y) (E). Scale bar is 5 μm.
Mentions: Fragmentation and immaturity similar to that observed in nidogen-2 mutants has been reported in collagen α5(IV) and laminin α4 mutants and in laminin α4/α5 double mutants, respectively [12,18,19]. However, nidogen-2 remained concentrated in the synaptic BL of NMJs in all of these mutants (Figure 9). Thus, synaptic laminins and collagens IV are dispensable for concentrating nidogen-2 in the synaptic cleft. Moreover, the absence of nidogen-2 is not responsible for fragmentation of synapses lacking synaptic laminins or collagens IV.

Bottom Line: All four core components of the basal lamina have synaptically enriched isoforms.Together, they form a highly specialized synaptic cleft material.Individually, they play distinct roles in the formation, maturation and maintenance of the neuromuscular junction.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Molecular and Cellular Biology and Center for Brain Science, Harvard University, Cambridge, MA 02138, USA. mafox@vcu.edu

ABSTRACT

Background: The skeletal neuromuscular junction is a useful model for elucidating mechanisms that regulate synaptogenesis. Developmentally important intercellular interactions at the neuromuscular junction are mediated by the synaptic portion of a basal lamina that completely ensheaths each muscle fiber. Basal laminas in general are composed of four main types of glycosylated proteins: laminins, collagens IV, heparan sulfate proteoglycans and nidogens (entactins). The portion of the muscle fiber basal lamina that passes between the motor nerve terminal and postsynaptic membrane has been shown to bear distinct isoforms of the first three of these. For laminins and collagens IV, the proteins are deposited by the muscle; a synaptic proteoglycan, z-agrin, is deposited by the nerve. In each case, the synaptic isoform plays key roles in organizing the neuromuscular junction. Here, we analyze the fourth family, composed of nidogen-1 and -2.

Results: In adult muscle, nidogen-1 is present throughout muscle fiber basal lamina, while nidogen-2 is concentrated at synapses. Nidogen-2 is initially present throughout muscle basal lamina, but is lost from extrasynaptic regions during the first three postnatal weeks. Neuromuscular junctions in mutant mice lacking nidogen-2 appear normal at birth, but become topologically abnormal as they mature. Synaptic laminins, collagens IV and heparan sulfate proteoglycans persist in the absence of nidogen-2, suggesting the phenotype is not secondary to a general defect in the integrity of synaptic basal lamina. Further genetic studies suggest that synaptic localization of each of the four families of synaptic basal lamina components is independent of the other three.

Conclusion: All four core components of the basal lamina have synaptically enriched isoforms. Together, they form a highly specialized synaptic cleft material. Individually, they play distinct roles in the formation, maturation and maintenance of the neuromuscular junction.

Show MeSH
Related in: MedlinePlus