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Agrin mediates a rapid switch from electrical coupling to chemical neurotransmission during synaptogenesis.

Martin AO, Alonso G, Guérineau NC - J. Cell Biol. (2005)

Bottom Line: When applied at the developing splanchnic nerve-chromaffin cell cholinergic synapse in rat adrenal acute slices, agrin rapidly modified cell-to-cell communication mechanisms.This developmental switch from predominantly electrical to chemical communication was fully operational within one hour and depended on the activation of Src family-related tyrosine kinases.Hence, agrin may play a pivotal role in synaptogenesis in promoting a rapid switch between electrical coupling and synaptic neurotransmission.

View Article: PubMed Central - PubMed

Affiliation: CNRS UMR5203, INSERM U661, Université Montpellier I, Département d'Endocrinologie, Institut de Génomique Fonctionnelle, 34094 Montpellier Cedex 5, France.

ABSTRACT
In contrast to its well-established actions as an organizer of synaptic differentiation at the neuromuscular junction, the proteoglycan agrin is still in search of a function in the nervous system. Here, we report an entirely unanticipated role for agrin in the dual modulation of electrical and chemical intercellular communication that occurs during the critical period of synapse formation. When applied at the developing splanchnic nerve-chromaffin cell cholinergic synapse in rat adrenal acute slices, agrin rapidly modified cell-to-cell communication mechanisms. Specifically, it led to decreased gap junction-mediated electrical coupling that preceded an increase in nicotinic synaptic transmission. This developmental switch from predominantly electrical to chemical communication was fully operational within one hour and depended on the activation of Src family-related tyrosine kinases. Hence, agrin may play a pivotal role in synaptogenesis in promoting a rapid switch between electrical coupling and synaptic neurotransmission.

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Agrin expression in adult and newborn rat adrenal glands. (A and B) Western blots showing that total agrin or the Z+ variant is highly expressed in adults (3 glands) and more weakly detected in neonates (6 glands). (C) Double immunofluorescent detection of total agrin and its Z+ isoform combined with TH staining to visualize chromaffin cells in both adult (a) and neonatal (b) adrenal medulla. (D) Preferential expression of the Z+ variant at cholinergic synaptic contacts stained by the VAChT (white arrows).
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fig1: Agrin expression in adult and newborn rat adrenal glands. (A and B) Western blots showing that total agrin or the Z+ variant is highly expressed in adults (3 glands) and more weakly detected in neonates (6 glands). (C) Double immunofluorescent detection of total agrin and its Z+ isoform combined with TH staining to visualize chromaffin cells in both adult (a) and neonatal (b) adrenal medulla. (D) Preferential expression of the Z+ variant at cholinergic synaptic contacts stained by the VAChT (white arrows).

Mentions: Agrin was detected by Western blot from whole adrenal glands of adults and neonates. Total agrin was recognized as a single band of ∼200 kD (Fig. 1 A), as reported previously (Rupp et al., 1991). Kidney protein extracts were used as positive controls (Groffen et al., 1998). The expression level of total agrin and its Z+ variant, which has been reported as the most potent isoform in clustering nicotinic acetylcholine receptors (nAChRs) at the NMJ (Ferns et al., 1992), underwent up-regulation during adrenal gland postnatal development, as indicated by a weaker expression in neonates when compared with adults (Fig. 1 B). To characterize the tissular localization of agrin, a double-immunofluorescent detection of total agrin and the Z+ insert-containing isoform was combined with tyrosine hydroxylase (TH) staining to visualize chromaffin cells. In adults, intense staining for both total agrin and the Z+ variant was detected throughout the medulla outlining chromaffin cell clusters (Fig. 1 C, a). By contrast, neonate medulla displayed faint labeling for agrin (Fig. 1 C, b). Both agrin isoforms were likely apposed to the ECM, as evidenced by colocalization with laminin (unpublished data). In adults, the Z+ variant was preferentially expressed at cholinergic synaptic contacts, which were stained by a vesicular acetylcholine transporter (VAChT)–specific antibody (Fig. 1 D), suggesting that agrin likely originated from cholinergic neurons synapsing onto chromaffin cells. Agrin was never detected in chromaffin cells, ruling out a possible autocrine/paracrine mechanism of action.


Agrin mediates a rapid switch from electrical coupling to chemical neurotransmission during synaptogenesis.

Martin AO, Alonso G, Guérineau NC - J. Cell Biol. (2005)

Agrin expression in adult and newborn rat adrenal glands. (A and B) Western blots showing that total agrin or the Z+ variant is highly expressed in adults (3 glands) and more weakly detected in neonates (6 glands). (C) Double immunofluorescent detection of total agrin and its Z+ isoform combined with TH staining to visualize chromaffin cells in both adult (a) and neonatal (b) adrenal medulla. (D) Preferential expression of the Z+ variant at cholinergic synaptic contacts stained by the VAChT (white arrows).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2171940&req=5

fig1: Agrin expression in adult and newborn rat adrenal glands. (A and B) Western blots showing that total agrin or the Z+ variant is highly expressed in adults (3 glands) and more weakly detected in neonates (6 glands). (C) Double immunofluorescent detection of total agrin and its Z+ isoform combined with TH staining to visualize chromaffin cells in both adult (a) and neonatal (b) adrenal medulla. (D) Preferential expression of the Z+ variant at cholinergic synaptic contacts stained by the VAChT (white arrows).
Mentions: Agrin was detected by Western blot from whole adrenal glands of adults and neonates. Total agrin was recognized as a single band of ∼200 kD (Fig. 1 A), as reported previously (Rupp et al., 1991). Kidney protein extracts were used as positive controls (Groffen et al., 1998). The expression level of total agrin and its Z+ variant, which has been reported as the most potent isoform in clustering nicotinic acetylcholine receptors (nAChRs) at the NMJ (Ferns et al., 1992), underwent up-regulation during adrenal gland postnatal development, as indicated by a weaker expression in neonates when compared with adults (Fig. 1 B). To characterize the tissular localization of agrin, a double-immunofluorescent detection of total agrin and the Z+ insert-containing isoform was combined with tyrosine hydroxylase (TH) staining to visualize chromaffin cells. In adults, intense staining for both total agrin and the Z+ variant was detected throughout the medulla outlining chromaffin cell clusters (Fig. 1 C, a). By contrast, neonate medulla displayed faint labeling for agrin (Fig. 1 C, b). Both agrin isoforms were likely apposed to the ECM, as evidenced by colocalization with laminin (unpublished data). In adults, the Z+ variant was preferentially expressed at cholinergic synaptic contacts, which were stained by a vesicular acetylcholine transporter (VAChT)–specific antibody (Fig. 1 D), suggesting that agrin likely originated from cholinergic neurons synapsing onto chromaffin cells. Agrin was never detected in chromaffin cells, ruling out a possible autocrine/paracrine mechanism of action.

Bottom Line: When applied at the developing splanchnic nerve-chromaffin cell cholinergic synapse in rat adrenal acute slices, agrin rapidly modified cell-to-cell communication mechanisms.This developmental switch from predominantly electrical to chemical communication was fully operational within one hour and depended on the activation of Src family-related tyrosine kinases.Hence, agrin may play a pivotal role in synaptogenesis in promoting a rapid switch between electrical coupling and synaptic neurotransmission.

View Article: PubMed Central - PubMed

Affiliation: CNRS UMR5203, INSERM U661, Université Montpellier I, Département d'Endocrinologie, Institut de Génomique Fonctionnelle, 34094 Montpellier Cedex 5, France.

ABSTRACT
In contrast to its well-established actions as an organizer of synaptic differentiation at the neuromuscular junction, the proteoglycan agrin is still in search of a function in the nervous system. Here, we report an entirely unanticipated role for agrin in the dual modulation of electrical and chemical intercellular communication that occurs during the critical period of synapse formation. When applied at the developing splanchnic nerve-chromaffin cell cholinergic synapse in rat adrenal acute slices, agrin rapidly modified cell-to-cell communication mechanisms. Specifically, it led to decreased gap junction-mediated electrical coupling that preceded an increase in nicotinic synaptic transmission. This developmental switch from predominantly electrical to chemical communication was fully operational within one hour and depended on the activation of Src family-related tyrosine kinases. Hence, agrin may play a pivotal role in synaptogenesis in promoting a rapid switch between electrical coupling and synaptic neurotransmission.

Show MeSH
Related in: MedlinePlus