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Sonic hedgehog and notch signaling can cooperate to regulate neurogenic divisions of neocortical progenitors.

Dave RK, Ellis T, Toumpas MC, Robson JP, Julian E, Adolphe C, Bartlett PF, Cooper HM, Reynolds BA, Wainwright BJ - PLoS ONE (2011)

Bottom Line: The Notch signaling pathway plays a pivotal role in the maintenance of stem/progenitor cells and the regulation of glial versus neuronal identity.To study the effect of Notch signaling on Hh-activated neural progenitors, we inactivated both Patched1 and Rbpj, a transcriptional mediator of Notch signaling, in Nestin positive cells of the neocortex.Hence, our results demonstrate that correct corticogenesis is an outcome of the interplay between the Hh and Notch signaling pathways.

View Article: PubMed Central - PubMed

Affiliation: The Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia.

ABSTRACT

Background: Hedgehog (Hh) signaling is crucial for the generation and maintenance of both embryonic and adult stem cells, thereby regulating development and tissue homeostasis. In the developing neocortex, Sonic Hedgehog (Shh) regulates neural progenitor cell proliferation. During neurogenesis, radial glial cells of the ventricular zone (VZ) are the predominant neocortical progenitors that generate neurons through both symmetric and asymmetric divisions. Despite its importance, relatively little is known of the molecular pathways that control the switch from symmetric proliferative to differentiative/neurogenic divisions in neural progenitors.

Principal findings: Here, we report that conditional inactivation of Patched1, a negative regulator of the Shh pathway, in Nestin positive neural progenitors of the neocortex leads to lamination defects due to improper corticogenesis and an increase in the number of symmetric proliferative divisions of the radial glial cells. Hedgehog-activated VZ progenitor cells demonstrated a concomitant upregulation of Hes1 and Blbp, downstream targets of Notch signaling. The Notch signaling pathway plays a pivotal role in the maintenance of stem/progenitor cells and the regulation of glial versus neuronal identity. To study the effect of Notch signaling on Hh-activated neural progenitors, we inactivated both Patched1 and Rbpj, a transcriptional mediator of Notch signaling, in Nestin positive cells of the neocortex.

Conclusions: Our data indicate that by mid neurogenesis (embryonic day 14.5), attenuation of Notch signaling reverses the effect of Patched1 deletion on neurogenesis by restoring the balance between symmetric proliferative and neurogenic divisions. Hence, our results demonstrate that correct corticogenesis is an outcome of the interplay between the Hh and Notch signaling pathways.

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Inactivation of Ptc1 results in regulation of downstream targets of Notch signaling at E14.5.(A, B, C): Taqman RT-PCR for detection of Hes1, Hes5 and Blbp transcript from microdissected VZ (n≥3 for each genotype). Hes1 transcript was 65-fold upregulated in Ptc1Lox/Lox;NestinCre neocortex compared to Ptc1Lox/Lox VZ (A) and Blbp transcript was approximately two-fold upregulated compared to wild type VZ (p<0.05) (C). The expression of Hes1, Blbp and Hes5 was significantly downregulated following deletion of Rbpj compared to Ptc1 deletion alone (p<0.05). The data were normalised based on the expression of Gapdh.
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pone-0014680-g005: Inactivation of Ptc1 results in regulation of downstream targets of Notch signaling at E14.5.(A, B, C): Taqman RT-PCR for detection of Hes1, Hes5 and Blbp transcript from microdissected VZ (n≥3 for each genotype). Hes1 transcript was 65-fold upregulated in Ptc1Lox/Lox;NestinCre neocortex compared to Ptc1Lox/Lox VZ (A) and Blbp transcript was approximately two-fold upregulated compared to wild type VZ (p<0.05) (C). The expression of Hes1, Blbp and Hes5 was significantly downregulated following deletion of Rbpj compared to Ptc1 deletion alone (p<0.05). The data were normalised based on the expression of Gapdh.

Mentions: Clearly, our data indicate that Hedgehog pathway and Notch pathway activity can co-operate to regulate neurogenic divisions of neocortical progenitors. Therefore, we next examined whether the expansion of progenitor cells and the concomitant depletion of neurons in the VZ of E14.5 Ptc1Lox/Lox;NestinCre mice was potentially the result of the upregulation of Notch signaling. Figure 5A demonstrates that in wild type VZ Hes1 expression is low, and undetectable in the absence of Rbpj as expected. In the presence of Hedgehog pathway activation Hes1 activity is high but this activity is largely lost in the absence of Rbpj, suggesting that most of the Hedgehog-dependent Hes1 activity is dependent upon active canonical signaling. Interestingly, there is a minor component of Hh-dependent Hes1 activity that is not dependent upon Notch signaling, consistent with our results from the VZ of the cerebellum where there is also a Hedgehog and Notch-dependent Hes1 activity, and the data of others [46], [47], [48]. Overall, the Hes1 data indicate that in the developing VZ of the neocortex, Hedgehog pathway activation positively regulates Hes1 via Rbpj. Similarly, we analyzed Blbp expression (Figure 5C). Blbp has been shown to be a canonical Notch target in radial glial cells in the VZ [18]. Similar to Hes1, Blbp shows a distinct upregulation in response to activation of the Hedgehog pathway, and this activation is abrogated by loss of Rbpj. A third potential Notch effector in the VZ, Hes5 was also examined (Fig. 5B). From these data it can be observed that Hes5 expression requires Rbpj, as expected, but does not respond to Hedgehog pathway activation. On the whole, the data presented in Figure 5 suggest that the undoubted interaction observed at the developmental and stem cell level between Hedgehog and Notch signaling is reflected in part by an apparent Rbpj-dependent regulation by Hedgehog signaling of some, but not all, Notch effectors in the VZ.


Sonic hedgehog and notch signaling can cooperate to regulate neurogenic divisions of neocortical progenitors.

Dave RK, Ellis T, Toumpas MC, Robson JP, Julian E, Adolphe C, Bartlett PF, Cooper HM, Reynolds BA, Wainwright BJ - PLoS ONE (2011)

Inactivation of Ptc1 results in regulation of downstream targets of Notch signaling at E14.5.(A, B, C): Taqman RT-PCR for detection of Hes1, Hes5 and Blbp transcript from microdissected VZ (n≥3 for each genotype). Hes1 transcript was 65-fold upregulated in Ptc1Lox/Lox;NestinCre neocortex compared to Ptc1Lox/Lox VZ (A) and Blbp transcript was approximately two-fold upregulated compared to wild type VZ (p<0.05) (C). The expression of Hes1, Blbp and Hes5 was significantly downregulated following deletion of Rbpj compared to Ptc1 deletion alone (p<0.05). The data were normalised based on the expression of Gapdh.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3040755&req=5

pone-0014680-g005: Inactivation of Ptc1 results in regulation of downstream targets of Notch signaling at E14.5.(A, B, C): Taqman RT-PCR for detection of Hes1, Hes5 and Blbp transcript from microdissected VZ (n≥3 for each genotype). Hes1 transcript was 65-fold upregulated in Ptc1Lox/Lox;NestinCre neocortex compared to Ptc1Lox/Lox VZ (A) and Blbp transcript was approximately two-fold upregulated compared to wild type VZ (p<0.05) (C). The expression of Hes1, Blbp and Hes5 was significantly downregulated following deletion of Rbpj compared to Ptc1 deletion alone (p<0.05). The data were normalised based on the expression of Gapdh.
Mentions: Clearly, our data indicate that Hedgehog pathway and Notch pathway activity can co-operate to regulate neurogenic divisions of neocortical progenitors. Therefore, we next examined whether the expansion of progenitor cells and the concomitant depletion of neurons in the VZ of E14.5 Ptc1Lox/Lox;NestinCre mice was potentially the result of the upregulation of Notch signaling. Figure 5A demonstrates that in wild type VZ Hes1 expression is low, and undetectable in the absence of Rbpj as expected. In the presence of Hedgehog pathway activation Hes1 activity is high but this activity is largely lost in the absence of Rbpj, suggesting that most of the Hedgehog-dependent Hes1 activity is dependent upon active canonical signaling. Interestingly, there is a minor component of Hh-dependent Hes1 activity that is not dependent upon Notch signaling, consistent with our results from the VZ of the cerebellum where there is also a Hedgehog and Notch-dependent Hes1 activity, and the data of others [46], [47], [48]. Overall, the Hes1 data indicate that in the developing VZ of the neocortex, Hedgehog pathway activation positively regulates Hes1 via Rbpj. Similarly, we analyzed Blbp expression (Figure 5C). Blbp has been shown to be a canonical Notch target in radial glial cells in the VZ [18]. Similar to Hes1, Blbp shows a distinct upregulation in response to activation of the Hedgehog pathway, and this activation is abrogated by loss of Rbpj. A third potential Notch effector in the VZ, Hes5 was also examined (Fig. 5B). From these data it can be observed that Hes5 expression requires Rbpj, as expected, but does not respond to Hedgehog pathway activation. On the whole, the data presented in Figure 5 suggest that the undoubted interaction observed at the developmental and stem cell level between Hedgehog and Notch signaling is reflected in part by an apparent Rbpj-dependent regulation by Hedgehog signaling of some, but not all, Notch effectors in the VZ.

Bottom Line: The Notch signaling pathway plays a pivotal role in the maintenance of stem/progenitor cells and the regulation of glial versus neuronal identity.To study the effect of Notch signaling on Hh-activated neural progenitors, we inactivated both Patched1 and Rbpj, a transcriptional mediator of Notch signaling, in Nestin positive cells of the neocortex.Hence, our results demonstrate that correct corticogenesis is an outcome of the interplay between the Hh and Notch signaling pathways.

View Article: PubMed Central - PubMed

Affiliation: The Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia.

ABSTRACT

Background: Hedgehog (Hh) signaling is crucial for the generation and maintenance of both embryonic and adult stem cells, thereby regulating development and tissue homeostasis. In the developing neocortex, Sonic Hedgehog (Shh) regulates neural progenitor cell proliferation. During neurogenesis, radial glial cells of the ventricular zone (VZ) are the predominant neocortical progenitors that generate neurons through both symmetric and asymmetric divisions. Despite its importance, relatively little is known of the molecular pathways that control the switch from symmetric proliferative to differentiative/neurogenic divisions in neural progenitors.

Principal findings: Here, we report that conditional inactivation of Patched1, a negative regulator of the Shh pathway, in Nestin positive neural progenitors of the neocortex leads to lamination defects due to improper corticogenesis and an increase in the number of symmetric proliferative divisions of the radial glial cells. Hedgehog-activated VZ progenitor cells demonstrated a concomitant upregulation of Hes1 and Blbp, downstream targets of Notch signaling. The Notch signaling pathway plays a pivotal role in the maintenance of stem/progenitor cells and the regulation of glial versus neuronal identity. To study the effect of Notch signaling on Hh-activated neural progenitors, we inactivated both Patched1 and Rbpj, a transcriptional mediator of Notch signaling, in Nestin positive cells of the neocortex.

Conclusions: Our data indicate that by mid neurogenesis (embryonic day 14.5), attenuation of Notch signaling reverses the effect of Patched1 deletion on neurogenesis by restoring the balance between symmetric proliferative and neurogenic divisions. Hence, our results demonstrate that correct corticogenesis is an outcome of the interplay between the Hh and Notch signaling pathways.

Show MeSH
Related in: MedlinePlus