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Cis-interactions between Notch and its ligands block ligand-independent Notch activity.

Palmer WH, Jia D, Deng WM - Elife (2014)

Bottom Line: Notch is further characterized by a twofold relationship with its Delta-Serrate (DSL) ligands, as ligands from opposing cells (trans-ligands) activate Notch, whereas ligands expressed in the same cell (cis-ligands) inhibit signaling.Furthermore, cis-ligands can reduce Notch activity in endogenous and genetically induced situations of elevated trans-ligand-independent Notch signaling.We conclude that cis-expressed ligands exert their repressive effect on Notch signaling in cases of trans-ligand-independent activation, and propose a new function of cis-inhibition which buffers cells against accidental Notch activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Science, Florida State University, Tallahassee, United States.

ABSTRACT
The Notch pathway is integrated into numerous developmental processes and therefore is fine-tuned on many levels, including receptor production, endocytosis, and degradation. Notch is further characterized by a twofold relationship with its Delta-Serrate (DSL) ligands, as ligands from opposing cells (trans-ligands) activate Notch, whereas ligands expressed in the same cell (cis-ligands) inhibit signaling. We show that cells without both cis- and trans-ligands can mediate Notch-dependent developmental events during Drosophila oogenesis, indicating ligand-independent Notch activity occurs when the receptor is free of cis- and trans-ligands. Furthermore, cis-ligands can reduce Notch activity in endogenous and genetically induced situations of elevated trans-ligand-independent Notch signaling. We conclude that cis-expressed ligands exert their repressive effect on Notch signaling in cases of trans-ligand-independent activation, and propose a new function of cis-inhibition which buffers cells against accidental Notch activity.

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Reduced Notch reporter activity in crystal cells was not caused by indirect effects on early ligand-dependent Notch signaling in prohaemocytes.Normal Hnt expression in crystal cells expressing green fluorescent protein (GFP) driven by lz-GAL4 (A) and in lz-GAL4 driving expression of UAS-SerWT (B). There was no noticeable effect on the proportion of cells expressing Hnt when UAS-SerWT was misexpressed. Illustrations show outlines of crystal cells with either no Hnt expression (white filling) or Hnt expression (red filling). Scale bars represent 20 μm.DOI:http://dx.doi.org/10.7554/eLife.04415.015
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fig4s3: Reduced Notch reporter activity in crystal cells was not caused by indirect effects on early ligand-dependent Notch signaling in prohaemocytes.Normal Hnt expression in crystal cells expressing green fluorescent protein (GFP) driven by lz-GAL4 (A) and in lz-GAL4 driving expression of UAS-SerWT (B). There was no noticeable effect on the proportion of cells expressing Hnt when UAS-SerWT was misexpressed. Illustrations show outlines of crystal cells with either no Hnt expression (white filling) or Hnt expression (red filling). Scale bars represent 20 μm.DOI:http://dx.doi.org/10.7554/eLife.04415.015

Mentions: To explore whether cis-acting ligands might block endogenous raised levels of ligand-independent Notch activation, in addition to the raised levels induced by genetic defects, we examined the effect of increased ligand expression in crystal cells in the larval lymph gland, which have recently been shown to have ligand-independent Notch activation (Mukherjee et al., 2011). Notch activity in crystal cells promotes cell survival, and decreased Notch activity leads to a ‘bursting’ phenotype (Mukherjee et al., 2011) (Figure 4—figure supplement 2B,E). Evidence for this bursting phenotype is provided by the disorganization of membrane-associated GFP (Mukherjee et al., 2011). Using Lozenge (Lz)-GAL4, a crystal cell lineage-specific driver (Terriente-Felix et al., 2013) to misexpress UAS-NotchRNAi or UAS-Serdel3 led to a significantly higher proportion of cells showed the ‘bursting’ phenotype than wild-type crystal cells (NotchRNAi p = 0.0434, Serdel3 p = 0.0286) (Figure 4—figure supplement 2A,B,E). Furthermore, overexpression of UAS-SerWT led to a significant decrease of the Notch reporter E(spl):mβ-CD2expression in mature crystal cells (Figure 4—figure supplement 2C,D,F). Reduced Notch reporter activity was not caused by indirect effects on early ligand-dependent Notch signaling in prohaemocytes, as Hnt, a Notch target in differentiating crystal cells, (Terriente-Felix et al., 2013) was unaffected by ligand misexpression (Figure 4—figure supplement 3A,B). These observations indicate that increased ligand expression in crystal cells decreases cell survival by blocking Notch ligand-independent activation, and therefore the buffering role of cis-expressed ligand can be extended to endogenous cases of DSL-independent Notch activity.


Cis-interactions between Notch and its ligands block ligand-independent Notch activity.

Palmer WH, Jia D, Deng WM - Elife (2014)

Reduced Notch reporter activity in crystal cells was not caused by indirect effects on early ligand-dependent Notch signaling in prohaemocytes.Normal Hnt expression in crystal cells expressing green fluorescent protein (GFP) driven by lz-GAL4 (A) and in lz-GAL4 driving expression of UAS-SerWT (B). There was no noticeable effect on the proportion of cells expressing Hnt when UAS-SerWT was misexpressed. Illustrations show outlines of crystal cells with either no Hnt expression (white filling) or Hnt expression (red filling). Scale bars represent 20 μm.DOI:http://dx.doi.org/10.7554/eLife.04415.015
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4286723&req=5

fig4s3: Reduced Notch reporter activity in crystal cells was not caused by indirect effects on early ligand-dependent Notch signaling in prohaemocytes.Normal Hnt expression in crystal cells expressing green fluorescent protein (GFP) driven by lz-GAL4 (A) and in lz-GAL4 driving expression of UAS-SerWT (B). There was no noticeable effect on the proportion of cells expressing Hnt when UAS-SerWT was misexpressed. Illustrations show outlines of crystal cells with either no Hnt expression (white filling) or Hnt expression (red filling). Scale bars represent 20 μm.DOI:http://dx.doi.org/10.7554/eLife.04415.015
Mentions: To explore whether cis-acting ligands might block endogenous raised levels of ligand-independent Notch activation, in addition to the raised levels induced by genetic defects, we examined the effect of increased ligand expression in crystal cells in the larval lymph gland, which have recently been shown to have ligand-independent Notch activation (Mukherjee et al., 2011). Notch activity in crystal cells promotes cell survival, and decreased Notch activity leads to a ‘bursting’ phenotype (Mukherjee et al., 2011) (Figure 4—figure supplement 2B,E). Evidence for this bursting phenotype is provided by the disorganization of membrane-associated GFP (Mukherjee et al., 2011). Using Lozenge (Lz)-GAL4, a crystal cell lineage-specific driver (Terriente-Felix et al., 2013) to misexpress UAS-NotchRNAi or UAS-Serdel3 led to a significantly higher proportion of cells showed the ‘bursting’ phenotype than wild-type crystal cells (NotchRNAi p = 0.0434, Serdel3 p = 0.0286) (Figure 4—figure supplement 2A,B,E). Furthermore, overexpression of UAS-SerWT led to a significant decrease of the Notch reporter E(spl):mβ-CD2expression in mature crystal cells (Figure 4—figure supplement 2C,D,F). Reduced Notch reporter activity was not caused by indirect effects on early ligand-dependent Notch signaling in prohaemocytes, as Hnt, a Notch target in differentiating crystal cells, (Terriente-Felix et al., 2013) was unaffected by ligand misexpression (Figure 4—figure supplement 3A,B). These observations indicate that increased ligand expression in crystal cells decreases cell survival by blocking Notch ligand-independent activation, and therefore the buffering role of cis-expressed ligand can be extended to endogenous cases of DSL-independent Notch activity.

Bottom Line: Notch is further characterized by a twofold relationship with its Delta-Serrate (DSL) ligands, as ligands from opposing cells (trans-ligands) activate Notch, whereas ligands expressed in the same cell (cis-ligands) inhibit signaling.Furthermore, cis-ligands can reduce Notch activity in endogenous and genetically induced situations of elevated trans-ligand-independent Notch signaling.We conclude that cis-expressed ligands exert their repressive effect on Notch signaling in cases of trans-ligand-independent activation, and propose a new function of cis-inhibition which buffers cells against accidental Notch activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Science, Florida State University, Tallahassee, United States.

ABSTRACT
The Notch pathway is integrated into numerous developmental processes and therefore is fine-tuned on many levels, including receptor production, endocytosis, and degradation. Notch is further characterized by a twofold relationship with its Delta-Serrate (DSL) ligands, as ligands from opposing cells (trans-ligands) activate Notch, whereas ligands expressed in the same cell (cis-ligands) inhibit signaling. We show that cells without both cis- and trans-ligands can mediate Notch-dependent developmental events during Drosophila oogenesis, indicating ligand-independent Notch activity occurs when the receptor is free of cis- and trans-ligands. Furthermore, cis-ligands can reduce Notch activity in endogenous and genetically induced situations of elevated trans-ligand-independent Notch signaling. We conclude that cis-expressed ligands exert their repressive effect on Notch signaling in cases of trans-ligand-independent activation, and propose a new function of cis-inhibition which buffers cells against accidental Notch activity.

Show MeSH
Related in: MedlinePlus