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Two Notch ligands, Dll1 and Jag1, are differently restricted in their range of action to control neurogenesis in the mammalian spinal cord.

Ramos C, Rocha S, Gaspar C, Henrique D - PLoS ONE (2010)

Bottom Line: In the presence of a functional Dll1 allele, V1 neurogenesis is restored to the levels detected in single Jag1 mutants, while dI6 neurogenesis returns to normal, thereby confirming that Dll1-mediated signalling compensates for Jag1 deletion in V1 and dI6 domains.Our results reveal that Dll1 and Jag1 are functionally equivalent in controlling the rate of neurogenesis within their expression domains.However, Jag1 can only activate Notch signalling within the V1 and dI6 domains, whereas Dll1 can signal to neural progenitors both inside and outside its domains of expression.

View Article: PubMed Central - PubMed

Affiliation: Faculdade de Medicina de Lisboa, Instituto de Medicina Molecular, Lisboa, Portugal.

ABSTRACT

Background: Notch signalling regulates neuronal differentiation in the vertebrate nervous system. In addition to a widespread function in maintaining neural progenitors, Notch signalling has also been involved in specific neuronal fate decisions. These functions are likely mediated by distinct Notch ligands, which show restricted expression patterns in the developing nervous system. Two ligands, in particular, are expressed in non-overlapping complementary domains of the embryonic spinal cord, with Jag1 being restricted to the V1 and dI6 progenitor domains, while Dll1 is expressed in the remaining domains. However, the specific contribution of different ligands to regulate neurogenesis in vertebrate embryos is still poorly understood.

Methodology/principal findings: In this work, we investigated the role of Jag1 and Dll1 during spinal cord neurogenesis, using conditional knockout mice where the two genes are deleted in the neuroepithelium, singly or in combination. Our analysis showed that Jag1 deletion leads to a modest increase in V1 interneurons, while dI6 neurogenesis was unaltered. This mild Jag1 phenotype contrasts with the strong neurogenic phenotype detected in Dll1 mutants and led us to hypothesize that neighbouring Dll1-expressing cells signal to V1 and dI6 progenitors and restore neurogenesis in the absence of Jag1. Analysis of double Dll1;Jag1 mutant embryos revealed a stronger increase in V1-derived interneurons and overproduction of dI6 interneurons. In the presence of a functional Dll1 allele, V1 neurogenesis is restored to the levels detected in single Jag1 mutants, while dI6 neurogenesis returns to normal, thereby confirming that Dll1-mediated signalling compensates for Jag1 deletion in V1 and dI6 domains.

Conclusions/significance: Our results reveal that Dll1 and Jag1 are functionally equivalent in controlling the rate of neurogenesis within their expression domains. However, Jag1 can only activate Notch signalling within the V1 and dI6 domains, whereas Dll1 can signal to neural progenitors both inside and outside its domains of expression.

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Notch signalling activity is maintained in the V1 domain of Jag1 single mutants.(A, B) At E11.5, expression of Hes5 mRNA can still be detected in the V1 domain (between dashed white lines) of Jag1 mutants, although levels seem reduced when compared to control spinal cords. (A′, B′) The gap of Dll1 mRNA expression, corresponding to Jag1+ V1 domain (between dashed white lines), is present in both control and Jag1 mutants. (A″, B″) Merge of double in situ hybridization for Dll1 and Hes5 showing that Hes5 mRNA is still present within Dll1− V1 cells of Jag1 mutants. Scale bar 20 µm. (C, D) High-resolution confocal images of double in situ hybridization for Dll1 and Hes5 confirm that inactivation of Jag1 does not abolish Notch signalling in the V1 domain (between dashed white lines). Images show the presence of Dll1+ cells in the V0 (dorsally to white dashed lines) and V2 (ventrally to white dashed lines) domains flanking Hes5+ V1 progenitors in the neuroepithelium of both control and Jag1 mutants. Scale bar 20 µm.
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pone-0015515-g005: Notch signalling activity is maintained in the V1 domain of Jag1 single mutants.(A, B) At E11.5, expression of Hes5 mRNA can still be detected in the V1 domain (between dashed white lines) of Jag1 mutants, although levels seem reduced when compared to control spinal cords. (A′, B′) The gap of Dll1 mRNA expression, corresponding to Jag1+ V1 domain (between dashed white lines), is present in both control and Jag1 mutants. (A″, B″) Merge of double in situ hybridization for Dll1 and Hes5 showing that Hes5 mRNA is still present within Dll1− V1 cells of Jag1 mutants. Scale bar 20 µm. (C, D) High-resolution confocal images of double in situ hybridization for Dll1 and Hes5 confirm that inactivation of Jag1 does not abolish Notch signalling in the V1 domain (between dashed white lines). Images show the presence of Dll1+ cells in the V0 (dorsally to white dashed lines) and V2 (ventrally to white dashed lines) domains flanking Hes5+ V1 progenitors in the neuroepithelium of both control and Jag1 mutants. Scale bar 20 µm.

Mentions: Given the mild V1 phenotype detected in Jag1 mutant embryos, we next asked whether Notch signalling continues to be active in the V1 domain, even in the complete absence of Jag1 protein in the mutant neuroepithelium. To address this, we analysed the expression of Hes5, the main target and effector of Notch activity in the developing spinal cord [9]. In situ hybridization with a Hes5 probe in Jag1f/f;NesCre and control embryos revealed that Hes5 mRNA expression is slightly diminished in the V1 domain of Jag1 mutants, but is still broadly detected in V1 progenitors (Fig. 5 A,B). Simultaneous detection of Dll1 mRNA expression shows that Dll1 transcription continues to be excluded from the V1 domain of Jag1f/f;NesCre embryos (Fig. 5). These findings confirm the absence of cross-inhibition between the two genes in the developing spinal cord, as previously suggested by studies in the chick embryo, where missexpression of Dll1 or Jag1 did not alter the endogenous expression domains of Jag1 and Dll1, respectively [15].


Two Notch ligands, Dll1 and Jag1, are differently restricted in their range of action to control neurogenesis in the mammalian spinal cord.

Ramos C, Rocha S, Gaspar C, Henrique D - PLoS ONE (2010)

Notch signalling activity is maintained in the V1 domain of Jag1 single mutants.(A, B) At E11.5, expression of Hes5 mRNA can still be detected in the V1 domain (between dashed white lines) of Jag1 mutants, although levels seem reduced when compared to control spinal cords. (A′, B′) The gap of Dll1 mRNA expression, corresponding to Jag1+ V1 domain (between dashed white lines), is present in both control and Jag1 mutants. (A″, B″) Merge of double in situ hybridization for Dll1 and Hes5 showing that Hes5 mRNA is still present within Dll1− V1 cells of Jag1 mutants. Scale bar 20 µm. (C, D) High-resolution confocal images of double in situ hybridization for Dll1 and Hes5 confirm that inactivation of Jag1 does not abolish Notch signalling in the V1 domain (between dashed white lines). Images show the presence of Dll1+ cells in the V0 (dorsally to white dashed lines) and V2 (ventrally to white dashed lines) domains flanking Hes5+ V1 progenitors in the neuroepithelium of both control and Jag1 mutants. Scale bar 20 µm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2991363&req=5

pone-0015515-g005: Notch signalling activity is maintained in the V1 domain of Jag1 single mutants.(A, B) At E11.5, expression of Hes5 mRNA can still be detected in the V1 domain (between dashed white lines) of Jag1 mutants, although levels seem reduced when compared to control spinal cords. (A′, B′) The gap of Dll1 mRNA expression, corresponding to Jag1+ V1 domain (between dashed white lines), is present in both control and Jag1 mutants. (A″, B″) Merge of double in situ hybridization for Dll1 and Hes5 showing that Hes5 mRNA is still present within Dll1− V1 cells of Jag1 mutants. Scale bar 20 µm. (C, D) High-resolution confocal images of double in situ hybridization for Dll1 and Hes5 confirm that inactivation of Jag1 does not abolish Notch signalling in the V1 domain (between dashed white lines). Images show the presence of Dll1+ cells in the V0 (dorsally to white dashed lines) and V2 (ventrally to white dashed lines) domains flanking Hes5+ V1 progenitors in the neuroepithelium of both control and Jag1 mutants. Scale bar 20 µm.
Mentions: Given the mild V1 phenotype detected in Jag1 mutant embryos, we next asked whether Notch signalling continues to be active in the V1 domain, even in the complete absence of Jag1 protein in the mutant neuroepithelium. To address this, we analysed the expression of Hes5, the main target and effector of Notch activity in the developing spinal cord [9]. In situ hybridization with a Hes5 probe in Jag1f/f;NesCre and control embryos revealed that Hes5 mRNA expression is slightly diminished in the V1 domain of Jag1 mutants, but is still broadly detected in V1 progenitors (Fig. 5 A,B). Simultaneous detection of Dll1 mRNA expression shows that Dll1 transcription continues to be excluded from the V1 domain of Jag1f/f;NesCre embryos (Fig. 5). These findings confirm the absence of cross-inhibition between the two genes in the developing spinal cord, as previously suggested by studies in the chick embryo, where missexpression of Dll1 or Jag1 did not alter the endogenous expression domains of Jag1 and Dll1, respectively [15].

Bottom Line: In the presence of a functional Dll1 allele, V1 neurogenesis is restored to the levels detected in single Jag1 mutants, while dI6 neurogenesis returns to normal, thereby confirming that Dll1-mediated signalling compensates for Jag1 deletion in V1 and dI6 domains.Our results reveal that Dll1 and Jag1 are functionally equivalent in controlling the rate of neurogenesis within their expression domains.However, Jag1 can only activate Notch signalling within the V1 and dI6 domains, whereas Dll1 can signal to neural progenitors both inside and outside its domains of expression.

View Article: PubMed Central - PubMed

Affiliation: Faculdade de Medicina de Lisboa, Instituto de Medicina Molecular, Lisboa, Portugal.

ABSTRACT

Background: Notch signalling regulates neuronal differentiation in the vertebrate nervous system. In addition to a widespread function in maintaining neural progenitors, Notch signalling has also been involved in specific neuronal fate decisions. These functions are likely mediated by distinct Notch ligands, which show restricted expression patterns in the developing nervous system. Two ligands, in particular, are expressed in non-overlapping complementary domains of the embryonic spinal cord, with Jag1 being restricted to the V1 and dI6 progenitor domains, while Dll1 is expressed in the remaining domains. However, the specific contribution of different ligands to regulate neurogenesis in vertebrate embryos is still poorly understood.

Methodology/principal findings: In this work, we investigated the role of Jag1 and Dll1 during spinal cord neurogenesis, using conditional knockout mice where the two genes are deleted in the neuroepithelium, singly or in combination. Our analysis showed that Jag1 deletion leads to a modest increase in V1 interneurons, while dI6 neurogenesis was unaltered. This mild Jag1 phenotype contrasts with the strong neurogenic phenotype detected in Dll1 mutants and led us to hypothesize that neighbouring Dll1-expressing cells signal to V1 and dI6 progenitors and restore neurogenesis in the absence of Jag1. Analysis of double Dll1;Jag1 mutant embryos revealed a stronger increase in V1-derived interneurons and overproduction of dI6 interneurons. In the presence of a functional Dll1 allele, V1 neurogenesis is restored to the levels detected in single Jag1 mutants, while dI6 neurogenesis returns to normal, thereby confirming that Dll1-mediated signalling compensates for Jag1 deletion in V1 and dI6 domains.

Conclusions/significance: Our results reveal that Dll1 and Jag1 are functionally equivalent in controlling the rate of neurogenesis within their expression domains. However, Jag1 can only activate Notch signalling within the V1 and dI6 domains, whereas Dll1 can signal to neural progenitors both inside and outside its domains of expression.

Show MeSH
Related in: MedlinePlus