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RGMa regulates cortical interneuron migration and differentiation.

O'Leary C, Cole SJ, Langford M, Hewage J, White A, Cooper HM - PLoS ONE (2013)

Bottom Line: Intriguingly, the alternative Neogenin ligand, Netrin-1, had no effect on migration.However, we observed complete abrogation of RGMa-induced chemorepulsion when newborn interneurons were simultaneously exposed to RGMa and Netrin-1 gradients, suggesting a novel mechanism for the tight regulation of RGMa-guided interneuron migration.We propose that during peak neurogenesis, repulsive RGMa-Neogenin interactions drive interneurons into the migratory corridor and prevent re-entry into the ventricular zone of the ganglionic eminences.

View Article: PubMed Central - PubMed

Affiliation: The University of Queensland, Queensland Brain Institute, Brisbane, Queensland, Australia.

ABSTRACT
The etiology of neuropsychiatric disorders, including schizophrenia and autism, has been linked to a failure to establish the intricate neural network comprising excitatory pyramidal and inhibitory interneurons during neocortex development. A large proportion of cortical inhibitory interneurons originate in the medial ganglionic eminence (MGE) of the ventral telencephalon and then migrate through the ventral subventricular zone, across the corticostriatal junction, into the embryonic cortex. Successful navigation of newborn interneurons through the complex environment of the ventral telencephalon is governed by spatiotemporally restricted deployment of both chemorepulsive and chemoattractive guidance cues which work in concert to create a migratory corridor. Despite the expanding list of interneuron guidance cues, cues responsible for preventing interneurons from re-entering the ventricular zone of the ganglionic eminences have not been well characterized. Here we provide evidence that the chemorepulsive axon guidance cue, RGMa (Repulsive Guidance Molecule a), may fulfill this function. The ventricular zone restricted expression of RGMa in the ganglionic eminences and the presence of its receptor, Neogenin, in the ventricular zone and on newborn and maturing MGE-derived interneurons implicates RGMa-Neogenin interactions in interneuron differentiation and migration. Using an in vitro approach, we show that RGMa promotes interneuron differentiation by potentiating neurite outgrowth. In addition, using in vitro explant and migration assays, we provide evidence that RGMa is a repulsive guidance cue for newborn interneurons migrating out of the ganglionic eminence ventricular zone. Intriguingly, the alternative Neogenin ligand, Netrin-1, had no effect on migration. However, we observed complete abrogation of RGMa-induced chemorepulsion when newborn interneurons were simultaneously exposed to RGMa and Netrin-1 gradients, suggesting a novel mechanism for the tight regulation of RGMa-guided interneuron migration. We propose that during peak neurogenesis, repulsive RGMa-Neogenin interactions drive interneurons into the migratory corridor and prevent re-entry into the ventricular zone of the ganglionic eminences.

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RGMa-mediated repulsion of newborn interneurons is suppressed by Netrin-1.(A) The extent of interneuron migration was calculated as the ratio of the distal to proximal area (guidance ratio) occupied by migrating cells. (B–E) Anti-βIII-tubulin immunolabeling (red) revealed the extent of interneuron migration out of E14.5 MGE VZ explants placed adjacent to agarose blocks containing control HEK293 cells (B), cells producing Netrin-1 (C), RGMa (D) or RGMa + Netrin-1 (E). Note the significant increase in neuron density on the distal side of the explant in the presence of RGMa (D). (E) Quantification of the guidance ratio for newborn interneuron migration out of the MGE explants in response to guidance cues. Dotted lines indicate the body of the explant. Control, n = 10; Netrin-1, n = 8; RGMa, n = 12; RGMa + Netrin-1, n = 7. *p<0.5, **p<0.01.
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pone-0081711-g005: RGMa-mediated repulsion of newborn interneurons is suppressed by Netrin-1.(A) The extent of interneuron migration was calculated as the ratio of the distal to proximal area (guidance ratio) occupied by migrating cells. (B–E) Anti-βIII-tubulin immunolabeling (red) revealed the extent of interneuron migration out of E14.5 MGE VZ explants placed adjacent to agarose blocks containing control HEK293 cells (B), cells producing Netrin-1 (C), RGMa (D) or RGMa + Netrin-1 (E). Note the significant increase in neuron density on the distal side of the explant in the presence of RGMa (D). (E) Quantification of the guidance ratio for newborn interneuron migration out of the MGE explants in response to guidance cues. Dotted lines indicate the body of the explant. Control, n = 10; Netrin-1, n = 8; RGMa, n = 12; RGMa + Netrin-1, n = 7. *p<0.5, **p<0.01.

Mentions: RGMa is known to induce a Neo-dependent chemorepulsive axon guidance response, whereas Netrin-1-Neo interactions are chemoattractive [33]–[36], [41]. The restricted localization of RGMa to the VZ of the ganglionic eminences and the expression of Neo on newborn interneurons suggested that RGMa-Neo interactions may repel newborn interneurons away from the VZ and along the migratory corridor leading to the cortex. In addition, Netrin-1 is known to be expressed in both the E14.5 ganglionic eminence VZ and the striatum [56], [61], suggesting that Netrin-1-dependent guidance may also influence interneuron migration. To investigate the migration of interneurons in response to RGMa and Netrin-1 we performed in vitro explant assays in which MGE explants were dissected from the E14.5 forebrain and apposed to agarose blocks containing cells that produced RGMa, Netrin-1, or RGMa and Netrin-1 together (Fig. 5). Control blocks contained cells transfected with the empty expression vector. Explants were cocultured for 48 hrs and then stained with anti-βIII-tubulin to label neurons migrating from the explants. The extent of migration from the explant towards (proximal quadrant) or away from (distal quadrant) the ligand source was assessed by the guidance ratio. The guidance ratio was calculated by dividing the area occupied by neurons in the distal quadrant by the equivalent area in the proximal quadrant (Fig. 5A) [27]. Guidance ratios with values greater than 1 indicate repulsion, whereas ratios less than 1 indicate attraction.


RGMa regulates cortical interneuron migration and differentiation.

O'Leary C, Cole SJ, Langford M, Hewage J, White A, Cooper HM - PLoS ONE (2013)

RGMa-mediated repulsion of newborn interneurons is suppressed by Netrin-1.(A) The extent of interneuron migration was calculated as the ratio of the distal to proximal area (guidance ratio) occupied by migrating cells. (B–E) Anti-βIII-tubulin immunolabeling (red) revealed the extent of interneuron migration out of E14.5 MGE VZ explants placed adjacent to agarose blocks containing control HEK293 cells (B), cells producing Netrin-1 (C), RGMa (D) or RGMa + Netrin-1 (E). Note the significant increase in neuron density on the distal side of the explant in the presence of RGMa (D). (E) Quantification of the guidance ratio for newborn interneuron migration out of the MGE explants in response to guidance cues. Dotted lines indicate the body of the explant. Control, n = 10; Netrin-1, n = 8; RGMa, n = 12; RGMa + Netrin-1, n = 7. *p<0.5, **p<0.01.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3842424&req=5

pone-0081711-g005: RGMa-mediated repulsion of newborn interneurons is suppressed by Netrin-1.(A) The extent of interneuron migration was calculated as the ratio of the distal to proximal area (guidance ratio) occupied by migrating cells. (B–E) Anti-βIII-tubulin immunolabeling (red) revealed the extent of interneuron migration out of E14.5 MGE VZ explants placed adjacent to agarose blocks containing control HEK293 cells (B), cells producing Netrin-1 (C), RGMa (D) or RGMa + Netrin-1 (E). Note the significant increase in neuron density on the distal side of the explant in the presence of RGMa (D). (E) Quantification of the guidance ratio for newborn interneuron migration out of the MGE explants in response to guidance cues. Dotted lines indicate the body of the explant. Control, n = 10; Netrin-1, n = 8; RGMa, n = 12; RGMa + Netrin-1, n = 7. *p<0.5, **p<0.01.
Mentions: RGMa is known to induce a Neo-dependent chemorepulsive axon guidance response, whereas Netrin-1-Neo interactions are chemoattractive [33]–[36], [41]. The restricted localization of RGMa to the VZ of the ganglionic eminences and the expression of Neo on newborn interneurons suggested that RGMa-Neo interactions may repel newborn interneurons away from the VZ and along the migratory corridor leading to the cortex. In addition, Netrin-1 is known to be expressed in both the E14.5 ganglionic eminence VZ and the striatum [56], [61], suggesting that Netrin-1-dependent guidance may also influence interneuron migration. To investigate the migration of interneurons in response to RGMa and Netrin-1 we performed in vitro explant assays in which MGE explants were dissected from the E14.5 forebrain and apposed to agarose blocks containing cells that produced RGMa, Netrin-1, or RGMa and Netrin-1 together (Fig. 5). Control blocks contained cells transfected with the empty expression vector. Explants were cocultured for 48 hrs and then stained with anti-βIII-tubulin to label neurons migrating from the explants. The extent of migration from the explant towards (proximal quadrant) or away from (distal quadrant) the ligand source was assessed by the guidance ratio. The guidance ratio was calculated by dividing the area occupied by neurons in the distal quadrant by the equivalent area in the proximal quadrant (Fig. 5A) [27]. Guidance ratios with values greater than 1 indicate repulsion, whereas ratios less than 1 indicate attraction.

Bottom Line: Intriguingly, the alternative Neogenin ligand, Netrin-1, had no effect on migration.However, we observed complete abrogation of RGMa-induced chemorepulsion when newborn interneurons were simultaneously exposed to RGMa and Netrin-1 gradients, suggesting a novel mechanism for the tight regulation of RGMa-guided interneuron migration.We propose that during peak neurogenesis, repulsive RGMa-Neogenin interactions drive interneurons into the migratory corridor and prevent re-entry into the ventricular zone of the ganglionic eminences.

View Article: PubMed Central - PubMed

Affiliation: The University of Queensland, Queensland Brain Institute, Brisbane, Queensland, Australia.

ABSTRACT
The etiology of neuropsychiatric disorders, including schizophrenia and autism, has been linked to a failure to establish the intricate neural network comprising excitatory pyramidal and inhibitory interneurons during neocortex development. A large proportion of cortical inhibitory interneurons originate in the medial ganglionic eminence (MGE) of the ventral telencephalon and then migrate through the ventral subventricular zone, across the corticostriatal junction, into the embryonic cortex. Successful navigation of newborn interneurons through the complex environment of the ventral telencephalon is governed by spatiotemporally restricted deployment of both chemorepulsive and chemoattractive guidance cues which work in concert to create a migratory corridor. Despite the expanding list of interneuron guidance cues, cues responsible for preventing interneurons from re-entering the ventricular zone of the ganglionic eminences have not been well characterized. Here we provide evidence that the chemorepulsive axon guidance cue, RGMa (Repulsive Guidance Molecule a), may fulfill this function. The ventricular zone restricted expression of RGMa in the ganglionic eminences and the presence of its receptor, Neogenin, in the ventricular zone and on newborn and maturing MGE-derived interneurons implicates RGMa-Neogenin interactions in interneuron differentiation and migration. Using an in vitro approach, we show that RGMa promotes interneuron differentiation by potentiating neurite outgrowth. In addition, using in vitro explant and migration assays, we provide evidence that RGMa is a repulsive guidance cue for newborn interneurons migrating out of the ganglionic eminence ventricular zone. Intriguingly, the alternative Neogenin ligand, Netrin-1, had no effect on migration. However, we observed complete abrogation of RGMa-induced chemorepulsion when newborn interneurons were simultaneously exposed to RGMa and Netrin-1 gradients, suggesting a novel mechanism for the tight regulation of RGMa-guided interneuron migration. We propose that during peak neurogenesis, repulsive RGMa-Neogenin interactions drive interneurons into the migratory corridor and prevent re-entry into the ventricular zone of the ganglionic eminences.

Show MeSH
Related in: MedlinePlus