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Populations of radial glial cells respond differently to reelin and neuregulin1 in a ferret model of cortical dysplasia.

Poluch S, Juliano SL - PLoS ONE (2010)

Bottom Line: Ferrets treated with MAM on E24 result in an overall decrease of BLBP expression; radial glia that continue to express BLBP, however, show only mild disruption compared with the strongly disrupted vimentin expressing radial glia.We further investigated the effects induced by reelin and found that signaling was mediated via VLDLR/Dab1/Pi3K activation while NRG1 signaling was mediated via erbB3/erbB4/Pi3K.We then tested whether radial glial repair correlated with improved neuronal migration.

View Article: PubMed Central - PubMed

Affiliation: Anatomy, Physiology, and Genetics, Uniformed Services University, Bethesda, Maryland, United States of America.

ABSTRACT
Radial glial cells play an essential role during corticogenesis through their function as neural precursors and guides of neuronal migration. Both reelin and neuregulin1 (NRG1) maintain the radial glial scaffold; they also induce expression of Brain Lipid Binding Protein (BLBP), a well known marker of radial glia. Although radial glia in normal ferrets express both vimentin and BLBP, this coexpression diverges at P3; vimentin is expressed in the radial glial processes, while BLBP appears in cells detached from the ventricular zone. Our lab developed a model of cortical dysplasia in the ferret, resulting in impaired migration of neurons into the cortical plate and disordered radial glia. This occurs after exposure to the antimitotic methylazoxymethanol (MAM) on the 24th day of development (E24). Ferrets treated with MAM on E24 result in an overall decrease of BLBP expression; radial glia that continue to express BLBP, however, show only mild disruption compared with the strongly disrupted vimentin expressing radial glia. When E24 MAM-treated organotypic slices are exposed to reelin or NRG1, the severely disrupted vimentin+ radial glial processes are repaired but the slightly disordered BLBP+ processes are not. The realignment of vimentin+ processes was linked with an increase of their BLBP expression. BLBP expressing radial glia are distinguished by being both less affected by MAM treatment and by attempts at repair. We further investigated the effects induced by reelin and found that signaling was mediated via VLDLR/Dab1/Pi3K activation while NRG1 signaling was mediated via erbB3/erbB4/Pi3K. We then tested whether radial glial repair correlated with improved neuronal migration. Repairing the radial glial scaffold is not sufficient to restore neuronal migration; although reelin improves migration of neurons toward the cortical plate signaling through ApoER2/Dab1/PI3K activation, NRG1 does not.

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Schematic view of the role of reelin and NRG1 during late corticogenesis in ferret.Reelin secreted by Cajal-Retzius cells assists the migration of neurons from the upper intermediate zone (IZ) toward the cortical plate (CP). This process requires the activation of ApoER2, Dab1 and Pi3K. The transition from lower IZ to upper IZ is reelin-independent but Pi3K-dependent. Radial glial elongation is also influenced by reelin via activation of VLDLR, Dab1 and Pi3K. NRG1 does not control radial-guided migration in ferret but controls radial glial elongation via activation of erbB3, erbB4 and Pi3K. BLBP expression in radial glial processes is correlated with their elongated morphology and can be upregulated by reelin and NRG1. CP: Cortical Plate; IZu-L: Upper and Lower Intermediate Zone; MZ: Marginal Zone.
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pone-0013709-g008: Schematic view of the role of reelin and NRG1 during late corticogenesis in ferret.Reelin secreted by Cajal-Retzius cells assists the migration of neurons from the upper intermediate zone (IZ) toward the cortical plate (CP). This process requires the activation of ApoER2, Dab1 and Pi3K. The transition from lower IZ to upper IZ is reelin-independent but Pi3K-dependent. Radial glial elongation is also influenced by reelin via activation of VLDLR, Dab1 and Pi3K. NRG1 does not control radial-guided migration in ferret but controls radial glial elongation via activation of erbB3, erbB4 and Pi3K. BLBP expression in radial glial processes is correlated with their elongated morphology and can be upregulated by reelin and NRG1. CP: Cortical Plate; IZu-L: Upper and Lower Intermediate Zone; MZ: Marginal Zone.

Mentions: Reelin not only repairs the radial glial scaffold but also facilitates the migration of neurons into the CP [39]. To understand the process induced by reelin, MAM treated organotypic slices were exposed to a pulse of BrdU (1 h) and incubated with reelin (reelin secreted by HEK cells or recombinant reelin) in the presence of drugs blocking specific steps of the reelin pathway. After 2 DIC, the positions of BrdU+ cells were analyzed in 3 different cortical regions: the cortical plate (CP), the upper (IZU) and lower (IZL) parts of the intermediate zone (as described in [39]) (Figure 5c–d). Results are reported in Table 3. In MAM treated slices incubated in plain medium or cocultured with control HEK cells, BrdU+ cells tend to scatter in all cortical layers (Figure 5A,B,J). However, in the presence of either the central fragment (recombinant reelin) or the full length reelin (reelin secreting HEK cells), BrdU+ cells strongly accumulate in the CP (Figure 5C,D,J). The majority of BrdU+ cells found in the CP, after 2 DIC, are also likely to be generated in the neocortical VZ since they express MAP2 but are GABA-negative (Figure 5K–N). Also when DiI crystals are placed in the ganglionic eminence of MAM treated slices, few DiI+ cells were found in the cortex after 2 DIC; about 3–4 days are needed for tangentially migrating cells to reach the neocortex [22]. No statistical differences in the distribution of BrdU+ cells were found when MAM slices were cocultured with reelin HEK cells in medium containing RAP or SP600125, suggesting that neuronal migration is mediated mainly by ApoER2, with little if any contribution from VLDLR (Figure 5E,F,J). By using pharmacologic blockade of specific elements of the reelin signaling pathway, we observed that accumulation of cells in the CP induced by exogenous reelin secreted by HEK cells required the activation of Dab1 (Figure 5G,J), and Pi3K (Figure 5H,J). After blockade of Dab1 with PP2, fewer cells reached the CP and many settled near the ventricular zone, only able to travel short distances. Inhibiting Pi3K had a greater effect in this distribution, suggesting that reelin is not the only signal needed to initiate neuronal migration. Finally, blocking GSK3β, an element downstream of Pi3K, did not prevent the effect induced by reelin since many BrdU+ cells are found in the CP (Figure 5I,J). Our data suggest that (1) reelin stimulates migration toward the CP via activation of ApoER2, in a Dab1- and Pi3K-dependent but VLDLR- and GSK3β-independent manner and (2) reelin-dependent signaling as well as reelin-independent but Pi3K-dependent signaling facilitate neuronal migration from lower IZ toward the CP (see Figure S1 and also Figure 8).


Populations of radial glial cells respond differently to reelin and neuregulin1 in a ferret model of cortical dysplasia.

Poluch S, Juliano SL - PLoS ONE (2010)

Schematic view of the role of reelin and NRG1 during late corticogenesis in ferret.Reelin secreted by Cajal-Retzius cells assists the migration of neurons from the upper intermediate zone (IZ) toward the cortical plate (CP). This process requires the activation of ApoER2, Dab1 and Pi3K. The transition from lower IZ to upper IZ is reelin-independent but Pi3K-dependent. Radial glial elongation is also influenced by reelin via activation of VLDLR, Dab1 and Pi3K. NRG1 does not control radial-guided migration in ferret but controls radial glial elongation via activation of erbB3, erbB4 and Pi3K. BLBP expression in radial glial processes is correlated with their elongated morphology and can be upregulated by reelin and NRG1. CP: Cortical Plate; IZu-L: Upper and Lower Intermediate Zone; MZ: Marginal Zone.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2965671&req=5

pone-0013709-g008: Schematic view of the role of reelin and NRG1 during late corticogenesis in ferret.Reelin secreted by Cajal-Retzius cells assists the migration of neurons from the upper intermediate zone (IZ) toward the cortical plate (CP). This process requires the activation of ApoER2, Dab1 and Pi3K. The transition from lower IZ to upper IZ is reelin-independent but Pi3K-dependent. Radial glial elongation is also influenced by reelin via activation of VLDLR, Dab1 and Pi3K. NRG1 does not control radial-guided migration in ferret but controls radial glial elongation via activation of erbB3, erbB4 and Pi3K. BLBP expression in radial glial processes is correlated with their elongated morphology and can be upregulated by reelin and NRG1. CP: Cortical Plate; IZu-L: Upper and Lower Intermediate Zone; MZ: Marginal Zone.
Mentions: Reelin not only repairs the radial glial scaffold but also facilitates the migration of neurons into the CP [39]. To understand the process induced by reelin, MAM treated organotypic slices were exposed to a pulse of BrdU (1 h) and incubated with reelin (reelin secreted by HEK cells or recombinant reelin) in the presence of drugs blocking specific steps of the reelin pathway. After 2 DIC, the positions of BrdU+ cells were analyzed in 3 different cortical regions: the cortical plate (CP), the upper (IZU) and lower (IZL) parts of the intermediate zone (as described in [39]) (Figure 5c–d). Results are reported in Table 3. In MAM treated slices incubated in plain medium or cocultured with control HEK cells, BrdU+ cells tend to scatter in all cortical layers (Figure 5A,B,J). However, in the presence of either the central fragment (recombinant reelin) or the full length reelin (reelin secreting HEK cells), BrdU+ cells strongly accumulate in the CP (Figure 5C,D,J). The majority of BrdU+ cells found in the CP, after 2 DIC, are also likely to be generated in the neocortical VZ since they express MAP2 but are GABA-negative (Figure 5K–N). Also when DiI crystals are placed in the ganglionic eminence of MAM treated slices, few DiI+ cells were found in the cortex after 2 DIC; about 3–4 days are needed for tangentially migrating cells to reach the neocortex [22]. No statistical differences in the distribution of BrdU+ cells were found when MAM slices were cocultured with reelin HEK cells in medium containing RAP or SP600125, suggesting that neuronal migration is mediated mainly by ApoER2, with little if any contribution from VLDLR (Figure 5E,F,J). By using pharmacologic blockade of specific elements of the reelin signaling pathway, we observed that accumulation of cells in the CP induced by exogenous reelin secreted by HEK cells required the activation of Dab1 (Figure 5G,J), and Pi3K (Figure 5H,J). After blockade of Dab1 with PP2, fewer cells reached the CP and many settled near the ventricular zone, only able to travel short distances. Inhibiting Pi3K had a greater effect in this distribution, suggesting that reelin is not the only signal needed to initiate neuronal migration. Finally, blocking GSK3β, an element downstream of Pi3K, did not prevent the effect induced by reelin since many BrdU+ cells are found in the CP (Figure 5I,J). Our data suggest that (1) reelin stimulates migration toward the CP via activation of ApoER2, in a Dab1- and Pi3K-dependent but VLDLR- and GSK3β-independent manner and (2) reelin-dependent signaling as well as reelin-independent but Pi3K-dependent signaling facilitate neuronal migration from lower IZ toward the CP (see Figure S1 and also Figure 8).

Bottom Line: Ferrets treated with MAM on E24 result in an overall decrease of BLBP expression; radial glia that continue to express BLBP, however, show only mild disruption compared with the strongly disrupted vimentin expressing radial glia.We further investigated the effects induced by reelin and found that signaling was mediated via VLDLR/Dab1/Pi3K activation while NRG1 signaling was mediated via erbB3/erbB4/Pi3K.We then tested whether radial glial repair correlated with improved neuronal migration.

View Article: PubMed Central - PubMed

Affiliation: Anatomy, Physiology, and Genetics, Uniformed Services University, Bethesda, Maryland, United States of America.

ABSTRACT
Radial glial cells play an essential role during corticogenesis through their function as neural precursors and guides of neuronal migration. Both reelin and neuregulin1 (NRG1) maintain the radial glial scaffold; they also induce expression of Brain Lipid Binding Protein (BLBP), a well known marker of radial glia. Although radial glia in normal ferrets express both vimentin and BLBP, this coexpression diverges at P3; vimentin is expressed in the radial glial processes, while BLBP appears in cells detached from the ventricular zone. Our lab developed a model of cortical dysplasia in the ferret, resulting in impaired migration of neurons into the cortical plate and disordered radial glia. This occurs after exposure to the antimitotic methylazoxymethanol (MAM) on the 24th day of development (E24). Ferrets treated with MAM on E24 result in an overall decrease of BLBP expression; radial glia that continue to express BLBP, however, show only mild disruption compared with the strongly disrupted vimentin expressing radial glia. When E24 MAM-treated organotypic slices are exposed to reelin or NRG1, the severely disrupted vimentin+ radial glial processes are repaired but the slightly disordered BLBP+ processes are not. The realignment of vimentin+ processes was linked with an increase of their BLBP expression. BLBP expressing radial glia are distinguished by being both less affected by MAM treatment and by attempts at repair. We further investigated the effects induced by reelin and found that signaling was mediated via VLDLR/Dab1/Pi3K activation while NRG1 signaling was mediated via erbB3/erbB4/Pi3K. We then tested whether radial glial repair correlated with improved neuronal migration. Repairing the radial glial scaffold is not sufficient to restore neuronal migration; although reelin improves migration of neurons toward the cortical plate signaling through ApoER2/Dab1/PI3K activation, NRG1 does not.

Show MeSH
Related in: MedlinePlus