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GluRdelta2 expression in the mature cerebellum of hotfoot mice promotes parallel fiber synaptogenesis and axonal competition.

Mandolesi G, Autuori E, Cesa R, Premoselli F, Cesare P, Strata P - PLoS ONE (2009)

Bottom Line: In the proximal domain, we observed the formation of new spines that were innervated by PFs and a reduction in contact with the CF; ie, the pattern of innervation in the PC shifted to favor the PF input.Moreover, ectopic expression of GluRdelta2 in HEK293 cells that were cocultured with granule cells or in cerebellar Golgi cells in the mature brain induced the formation of new PF contacts.Collectively, our observations show that GluRdelta2 is an adhesion molecule that induces the formation of PF contacts independently of its cellular localization and promotes heterosynaptic competition in the PC proximal dendritic domain.

View Article: PubMed Central - PubMed

Affiliation: EBRI-Santa Lucia Foundation (IRCCS), Rome, Italy. g.mandolesi@hsantalucia.it

ABSTRACT
Glutamate receptor delta 2 (GluRdelta2) is selectively expressed in the cerebellum, exclusively in the spines of the Purkinje cells (PCs) that are in contact with parallel fibers (PFs). Although its structure is similar to ionotropic glutamate receptors, it has no channel function and its ligand is unknown. The GluRdelta2- mice, such as knockout and hotfoot have profoundly altered cerebellar circuitry, which causes ataxia and impaired motor learning. Notably, GluRdelta2 in PC-PF synapses regulates their maturation and strengthening and induces long term depression (LTD). In addition, GluRdelta2 participates in the highly territorial competition between the two excitatory inputs to the PC; the climbing fiber (CF), which innervates the proximal dendritic compartment, and the PF, which is connected to spiny distal branchlets. Recently, studies have suggested that GluRdelta2 acts as an adhesion molecule in PF synaptogenesis. Here, we provide in vivo and in vitro evidence that supports this hypothesis. Through lentiviral rescue in hotfoot mice, we noted a recovery of PC-PF contacts in the distal dendritic domain. In the proximal domain, we observed the formation of new spines that were innervated by PFs and a reduction in contact with the CF; ie, the pattern of innervation in the PC shifted to favor the PF input. Moreover, ectopic expression of GluRdelta2 in HEK293 cells that were cocultured with granule cells or in cerebellar Golgi cells in the mature brain induced the formation of new PF contacts. Collectively, our observations show that GluRdelta2 is an adhesion molecule that induces the formation of PF contacts independently of its cellular localization and promotes heterosynaptic competition in the PC proximal dendritic domain.

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GluRδ2 promotes an increase in PF inputs on the PC proximal dendrite of δ2/GFP-ho mice.(A–F) Immunostaining of PF innervations (blue) on the PC proximal domain of δ2/GFP-ho mice (A–D) and GFP-ho mice (E–F). (A) In the δ2/GFP-ho group, numerous spines (arrowheads) bearing GluRδ2 (red, B) appear in the proximal domain, and the PF contacts, labeled with VGluT1 antibody (blue, C and D), are more numerous relative to GFP-ho mice (E–F). The overlap between GluRδ2 and the PF synaptic terminals appears as fuchsia (D). (G) Histogram shows the mean percentage of spines overlapping with VGluT1. A significant increase is observed in the δ2/GFP-ho mice relative to the GFP-ho and δ2/GFP-ho CTR groups and also to GFP-wt mice. These results show that in presence of GluRδ2, indicated as the percentage of spines expressing GluRδ2 (black column), the PF input has a competitive advantage. ***p<0.001. Error bars indicate SE. Scale bar: A–F = 2 µm.
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pone-0005243-g006: GluRδ2 promotes an increase in PF inputs on the PC proximal dendrite of δ2/GFP-ho mice.(A–F) Immunostaining of PF innervations (blue) on the PC proximal domain of δ2/GFP-ho mice (A–D) and GFP-ho mice (E–F). (A) In the δ2/GFP-ho group, numerous spines (arrowheads) bearing GluRδ2 (red, B) appear in the proximal domain, and the PF contacts, labeled with VGluT1 antibody (blue, C and D), are more numerous relative to GFP-ho mice (E–F). The overlap between GluRδ2 and the PF synaptic terminals appears as fuchsia (D). (G) Histogram shows the mean percentage of spines overlapping with VGluT1. A significant increase is observed in the δ2/GFP-ho mice relative to the GFP-ho and δ2/GFP-ho CTR groups and also to GFP-wt mice. These results show that in presence of GluRδ2, indicated as the percentage of spines expressing GluRδ2 (black column), the PF input has a competitive advantage. ***p<0.001. Error bars indicate SE. Scale bar: A–F = 2 µm.

Mentions: The marked reduction in CF inputs and the presence of new spines in the proximal dendritic domain led us to examine the distribution of PF inputs (Fig. 6A–F). We measured the mean density of spines and counted the spines that coincided with VGluT1 expression (Fig. 6G). In δ2/GFP-ho mice, the mean percentage of spines that made contact with VGluT1-positive synaptic terminals increased (78.2±0.3 SE; n = 535) versus GFP-ho (28.3±0.8 SE; n = 64) and GFP-wt (19.0±0.3 SE; n = 324) groups (one-way ANOVA, p<0.001; post hoc Holm-Sidack test, p<0.05). In δ2/GFP-ho CTR mice, the mean percentage (26.2±0.03 SE; n = 501) was not significantly different from the control groups (one-way ANOVA, p<0.001; post hoc Holm-Sidack test, p>0.05) (Fig. 6G).


GluRdelta2 expression in the mature cerebellum of hotfoot mice promotes parallel fiber synaptogenesis and axonal competition.

Mandolesi G, Autuori E, Cesa R, Premoselli F, Cesare P, Strata P - PLoS ONE (2009)

GluRδ2 promotes an increase in PF inputs on the PC proximal dendrite of δ2/GFP-ho mice.(A–F) Immunostaining of PF innervations (blue) on the PC proximal domain of δ2/GFP-ho mice (A–D) and GFP-ho mice (E–F). (A) In the δ2/GFP-ho group, numerous spines (arrowheads) bearing GluRδ2 (red, B) appear in the proximal domain, and the PF contacts, labeled with VGluT1 antibody (blue, C and D), are more numerous relative to GFP-ho mice (E–F). The overlap between GluRδ2 and the PF synaptic terminals appears as fuchsia (D). (G) Histogram shows the mean percentage of spines overlapping with VGluT1. A significant increase is observed in the δ2/GFP-ho mice relative to the GFP-ho and δ2/GFP-ho CTR groups and also to GFP-wt mice. These results show that in presence of GluRδ2, indicated as the percentage of spines expressing GluRδ2 (black column), the PF input has a competitive advantage. ***p<0.001. Error bars indicate SE. Scale bar: A–F = 2 µm.
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Related In: Results  -  Collection

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pone-0005243-g006: GluRδ2 promotes an increase in PF inputs on the PC proximal dendrite of δ2/GFP-ho mice.(A–F) Immunostaining of PF innervations (blue) on the PC proximal domain of δ2/GFP-ho mice (A–D) and GFP-ho mice (E–F). (A) In the δ2/GFP-ho group, numerous spines (arrowheads) bearing GluRδ2 (red, B) appear in the proximal domain, and the PF contacts, labeled with VGluT1 antibody (blue, C and D), are more numerous relative to GFP-ho mice (E–F). The overlap between GluRδ2 and the PF synaptic terminals appears as fuchsia (D). (G) Histogram shows the mean percentage of spines overlapping with VGluT1. A significant increase is observed in the δ2/GFP-ho mice relative to the GFP-ho and δ2/GFP-ho CTR groups and also to GFP-wt mice. These results show that in presence of GluRδ2, indicated as the percentage of spines expressing GluRδ2 (black column), the PF input has a competitive advantage. ***p<0.001. Error bars indicate SE. Scale bar: A–F = 2 µm.
Mentions: The marked reduction in CF inputs and the presence of new spines in the proximal dendritic domain led us to examine the distribution of PF inputs (Fig. 6A–F). We measured the mean density of spines and counted the spines that coincided with VGluT1 expression (Fig. 6G). In δ2/GFP-ho mice, the mean percentage of spines that made contact with VGluT1-positive synaptic terminals increased (78.2±0.3 SE; n = 535) versus GFP-ho (28.3±0.8 SE; n = 64) and GFP-wt (19.0±0.3 SE; n = 324) groups (one-way ANOVA, p<0.001; post hoc Holm-Sidack test, p<0.05). In δ2/GFP-ho CTR mice, the mean percentage (26.2±0.03 SE; n = 501) was not significantly different from the control groups (one-way ANOVA, p<0.001; post hoc Holm-Sidack test, p>0.05) (Fig. 6G).

Bottom Line: In the proximal domain, we observed the formation of new spines that were innervated by PFs and a reduction in contact with the CF; ie, the pattern of innervation in the PC shifted to favor the PF input.Moreover, ectopic expression of GluRdelta2 in HEK293 cells that were cocultured with granule cells or in cerebellar Golgi cells in the mature brain induced the formation of new PF contacts.Collectively, our observations show that GluRdelta2 is an adhesion molecule that induces the formation of PF contacts independently of its cellular localization and promotes heterosynaptic competition in the PC proximal dendritic domain.

View Article: PubMed Central - PubMed

Affiliation: EBRI-Santa Lucia Foundation (IRCCS), Rome, Italy. g.mandolesi@hsantalucia.it

ABSTRACT
Glutamate receptor delta 2 (GluRdelta2) is selectively expressed in the cerebellum, exclusively in the spines of the Purkinje cells (PCs) that are in contact with parallel fibers (PFs). Although its structure is similar to ionotropic glutamate receptors, it has no channel function and its ligand is unknown. The GluRdelta2- mice, such as knockout and hotfoot have profoundly altered cerebellar circuitry, which causes ataxia and impaired motor learning. Notably, GluRdelta2 in PC-PF synapses regulates their maturation and strengthening and induces long term depression (LTD). In addition, GluRdelta2 participates in the highly territorial competition between the two excitatory inputs to the PC; the climbing fiber (CF), which innervates the proximal dendritic compartment, and the PF, which is connected to spiny distal branchlets. Recently, studies have suggested that GluRdelta2 acts as an adhesion molecule in PF synaptogenesis. Here, we provide in vivo and in vitro evidence that supports this hypothesis. Through lentiviral rescue in hotfoot mice, we noted a recovery of PC-PF contacts in the distal dendritic domain. In the proximal domain, we observed the formation of new spines that were innervated by PFs and a reduction in contact with the CF; ie, the pattern of innervation in the PC shifted to favor the PF input. Moreover, ectopic expression of GluRdelta2 in HEK293 cells that were cocultured with granule cells or in cerebellar Golgi cells in the mature brain induced the formation of new PF contacts. Collectively, our observations show that GluRdelta2 is an adhesion molecule that induces the formation of PF contacts independently of its cellular localization and promotes heterosynaptic competition in the PC proximal dendritic domain.

Show MeSH
Related in: MedlinePlus