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The atypical mammalian ligand Delta-like homologue 1 (Dlk1) can regulate Notch signalling in Drosophila.

Bray SJ, Takada S, Harrison E, Shen SC, Ferguson-Smith AC - BMC Dev. Biol. (2008)

Bottom Line: The resulting adult phenotypes are indicative of reduced Notch function and are enhanced by Notch mutations, confirming that DLK1 action is antagonistic.In addition, cells expressing an alternative Dlk1 isoform exhibit alterations in cell size, functions previously not attributed to Notch suggesting that DLK1 might also act via an alternative target.Our results demonstrate that DLK1 can regulate the Notch receptor despite its atypical structure.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology, Development, and Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3DY, UK. sjb32@cam.ac.uk

ABSTRACT

Background: Mammalian Delta-like 1 (Dlk-1) protein shares homology with Notch ligands but lacks a critical receptor-binding domain. Thus it is unclear whether it is able to interact with Notch in vivo. Unlike mammals, Drosophila have a single Notch receptor allowing a simple in vivo assay for mammalian Dlk1 function.

Results: Here we show that membrane-bound DLK1 can regulate Notch leading to altered cellular distribution of Notch itself and inhibiting expression of Notch target genes. The resulting adult phenotypes are indicative of reduced Notch function and are enhanced by Notch mutations, confirming that DLK1 action is antagonistic. In addition, cells expressing an alternative Dlk1 isoform exhibit alterations in cell size, functions previously not attributed to Notch suggesting that DLK1 might also act via an alternative target.

Conclusion: Our results demonstrate that DLK1 can regulate the Notch receptor despite its atypical structure.

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Expression of Dlk1 alters the cellular distribution of Notch. (A-C) M-Dlk (A,A" green, white) is present at the cortex/membrane of expressing cells and results in stabilization of Notch (A,A', B,B', C,C' red, white) within the stripe of M-Dlk expression (yellow arrows/line). (B-B") Higher magnification, cell outlines with M-Dlk and Notch enrichment are visible (e.g. arrowhead). (C-C") X/Z section, co-enrichment of Notch and M-Dlk on apical and lateral regions of cells is seen (e.g. arrowhead; note there is also non-specific accumulation of anti-Dlk staining along the surface of the specimen). (D-E) SM-Dlk (D, D"; E, E"; green, white) accumulates on the basal surface of the epithelium (e.g. arrow in E,E"), and at lower levels around the membrane/cortical regions. Less stabilisation/accumulation of Notch is detected, but there is enrichment at the cortex of some SM-Dlk expressing cells (e.g. arrowheads). (A'-E') Notch channels only, (A"-E") anti-Dlk channels only. Yellow arrows and lines indicate domain of ptc::Gal4 driven expression.
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Figure 4: Expression of Dlk1 alters the cellular distribution of Notch. (A-C) M-Dlk (A,A" green, white) is present at the cortex/membrane of expressing cells and results in stabilization of Notch (A,A', B,B', C,C' red, white) within the stripe of M-Dlk expression (yellow arrows/line). (B-B") Higher magnification, cell outlines with M-Dlk and Notch enrichment are visible (e.g. arrowhead). (C-C") X/Z section, co-enrichment of Notch and M-Dlk on apical and lateral regions of cells is seen (e.g. arrowhead; note there is also non-specific accumulation of anti-Dlk staining along the surface of the specimen). (D-E) SM-Dlk (D, D"; E, E"; green, white) accumulates on the basal surface of the epithelium (e.g. arrow in E,E"), and at lower levels around the membrane/cortical regions. Less stabilisation/accumulation of Notch is detected, but there is enrichment at the cortex of some SM-Dlk expressing cells (e.g. arrowheads). (A'-E') Notch channels only, (A"-E") anti-Dlk channels only. Yellow arrows and lines indicate domain of ptc::Gal4 driven expression.

Mentions: The differing severity of the M-Dlk and SM-Dlk might in part be due to the transgenes being expressed at different levels. However, the fact that even increasing the dosage and temperature failed to properly redress the difference, and that the two proteins had distinct effects on proliferation suggested that there are intrinsic differences in the behaviours of the proteins. To investigate these questions we stained wing discs with an antibody that recognises DLK1. This revealed a striking difference in the behaviour of the two proteins. M-Dlk had a cortical/membrane distribution (Fig. 4B,B',C,C'), whereas SM-Dlk accumulated at highest levels basally, although some membrane associated protein was detectable (Fig. 4D,D",E,E").


The atypical mammalian ligand Delta-like homologue 1 (Dlk1) can regulate Notch signalling in Drosophila.

Bray SJ, Takada S, Harrison E, Shen SC, Ferguson-Smith AC - BMC Dev. Biol. (2008)

Expression of Dlk1 alters the cellular distribution of Notch. (A-C) M-Dlk (A,A" green, white) is present at the cortex/membrane of expressing cells and results in stabilization of Notch (A,A', B,B', C,C' red, white) within the stripe of M-Dlk expression (yellow arrows/line). (B-B") Higher magnification, cell outlines with M-Dlk and Notch enrichment are visible (e.g. arrowhead). (C-C") X/Z section, co-enrichment of Notch and M-Dlk on apical and lateral regions of cells is seen (e.g. arrowhead; note there is also non-specific accumulation of anti-Dlk staining along the surface of the specimen). (D-E) SM-Dlk (D, D"; E, E"; green, white) accumulates on the basal surface of the epithelium (e.g. arrow in E,E"), and at lower levels around the membrane/cortical regions. Less stabilisation/accumulation of Notch is detected, but there is enrichment at the cortex of some SM-Dlk expressing cells (e.g. arrowheads). (A'-E') Notch channels only, (A"-E") anti-Dlk channels only. Yellow arrows and lines indicate domain of ptc::Gal4 driven expression.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2268666&req=5

Figure 4: Expression of Dlk1 alters the cellular distribution of Notch. (A-C) M-Dlk (A,A" green, white) is present at the cortex/membrane of expressing cells and results in stabilization of Notch (A,A', B,B', C,C' red, white) within the stripe of M-Dlk expression (yellow arrows/line). (B-B") Higher magnification, cell outlines with M-Dlk and Notch enrichment are visible (e.g. arrowhead). (C-C") X/Z section, co-enrichment of Notch and M-Dlk on apical and lateral regions of cells is seen (e.g. arrowhead; note there is also non-specific accumulation of anti-Dlk staining along the surface of the specimen). (D-E) SM-Dlk (D, D"; E, E"; green, white) accumulates on the basal surface of the epithelium (e.g. arrow in E,E"), and at lower levels around the membrane/cortical regions. Less stabilisation/accumulation of Notch is detected, but there is enrichment at the cortex of some SM-Dlk expressing cells (e.g. arrowheads). (A'-E') Notch channels only, (A"-E") anti-Dlk channels only. Yellow arrows and lines indicate domain of ptc::Gal4 driven expression.
Mentions: The differing severity of the M-Dlk and SM-Dlk might in part be due to the transgenes being expressed at different levels. However, the fact that even increasing the dosage and temperature failed to properly redress the difference, and that the two proteins had distinct effects on proliferation suggested that there are intrinsic differences in the behaviours of the proteins. To investigate these questions we stained wing discs with an antibody that recognises DLK1. This revealed a striking difference in the behaviour of the two proteins. M-Dlk had a cortical/membrane distribution (Fig. 4B,B',C,C'), whereas SM-Dlk accumulated at highest levels basally, although some membrane associated protein was detectable (Fig. 4D,D",E,E").

Bottom Line: The resulting adult phenotypes are indicative of reduced Notch function and are enhanced by Notch mutations, confirming that DLK1 action is antagonistic.In addition, cells expressing an alternative Dlk1 isoform exhibit alterations in cell size, functions previously not attributed to Notch suggesting that DLK1 might also act via an alternative target.Our results demonstrate that DLK1 can regulate the Notch receptor despite its atypical structure.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology, Development, and Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3DY, UK. sjb32@cam.ac.uk

ABSTRACT

Background: Mammalian Delta-like 1 (Dlk-1) protein shares homology with Notch ligands but lacks a critical receptor-binding domain. Thus it is unclear whether it is able to interact with Notch in vivo. Unlike mammals, Drosophila have a single Notch receptor allowing a simple in vivo assay for mammalian Dlk1 function.

Results: Here we show that membrane-bound DLK1 can regulate Notch leading to altered cellular distribution of Notch itself and inhibiting expression of Notch target genes. The resulting adult phenotypes are indicative of reduced Notch function and are enhanced by Notch mutations, confirming that DLK1 action is antagonistic. In addition, cells expressing an alternative Dlk1 isoform exhibit alterations in cell size, functions previously not attributed to Notch suggesting that DLK1 might also act via an alternative target.

Conclusion: Our results demonstrate that DLK1 can regulate the Notch receptor despite its atypical structure.

Show MeSH