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Nkd1 functions as a passive antagonist of Wnt signaling.

Angonin D, Van Raay TJ - PLoS ONE (2013)

Bottom Line: There are several Wnt negative feedback regulators, which are active antagonists of Wnt signaling, but one feedback regulator, Nkd1, has reduced activity compared to other antagonists, yet is still a negative feedback regulator.While slb and tri mutants do not display alterations in canonical Wnt signaling, we found that they are hypersensitive to it.These results suggest that Nkd1 functions as a passive antagonist of Wnt signaling, functioning only when homeostatic levels of Wnt signaling have been breached or when Wnt signaling becomes destabilized.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.

ABSTRACT
Wnt signaling is involved in many aspects of development and in the homeostasis of stem cells. Its importance is underscored by the fact that misregulation of Wnt signaling has been implicated in numerous diseases, especially colorectal cancer. However, how Wnt signaling regulates itself is not well understood. There are several Wnt negative feedback regulators, which are active antagonists of Wnt signaling, but one feedback regulator, Nkd1, has reduced activity compared to other antagonists, yet is still a negative feedback regulator. Here we describe our efforts to understand the role of Nkd1 using Wnt signaling compromised zebrafish mutant lines. In several of these lines, Nkd1 function was not any more active than it was in wild type embryos. However, we found that Nkd1's ability to antagonize canonical Wnt/β-catenin signaling was enhanced in the Wnt/Planar Cell Polarity mutants silberblick (slb/wnt11) and trilobite (tri/vangl2). While slb and tri mutants do not display alterations in canonical Wnt signaling, we found that they are hypersensitive to it. Overexpression of the canonical Wnt/β-catenin ligand Wnt8a in slb or tri mutants resulted in dorsalized embryos, with tri mutants being much more sensitive to Wnt8a than slb mutants. Furthermore, the hyperdorsalization caused by Wnt8a in tri could be rescued by Nkd1. These results suggest that Nkd1 functions as a passive antagonist of Wnt signaling, functioning only when homeostatic levels of Wnt signaling have been breached or when Wnt signaling becomes destabilized.

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Nkd1 is sufficient to antagonize ectopic Wnt8a.Overexpression of Wnt8a (25pg) results in an eyeless phenotype that can be rescued by co-injection of nkd1 (A, B) which is quantified in (C). Numbers above each column represent n values. Overexpression of high Wnt8a (200pg) results in ectopic gsc expression along the ventral-lateral domain at 50% epiboly (E). Co-injection of high wnt8a with nkd1 mRNAs dramatically reduces the ectopic gsc expression, but leaves the putative endogenous gsc domain intact (F).
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pone-0074666-g002: Nkd1 is sufficient to antagonize ectopic Wnt8a.Overexpression of Wnt8a (25pg) results in an eyeless phenotype that can be rescued by co-injection of nkd1 (A, B) which is quantified in (C). Numbers above each column represent n values. Overexpression of high Wnt8a (200pg) results in ectopic gsc expression along the ventral-lateral domain at 50% epiboly (E). Co-injection of high wnt8a with nkd1 mRNAs dramatically reduces the ectopic gsc expression, but leaves the putative endogenous gsc domain intact (F).

Mentions: While Nkd1 has little apparent affect on overall development, it is still sufficient to antagonize Wnt signaling, although to varying degrees dependent on if it is endogenous or exogenous Wnt signaling (Figure 2). Overexpression of Wnt8 in zebrafish embryos results in an eyeless phenotype at 1 dpf, which is effectively rescued by Nkd1 and overall development appears normal, albeit with a smaller eye (Figure 2A–C). Similarly, Wnt8 can induce ectopic gsc expression at 50% epiboly, which is also effectively reduced by the addition of Nkd1 (Figure 2D–F). Note however, that there is also a subtle effect on endogenous Wnt signaling: expansion of dorsal gsc expression (Figure 2F). This is consistent with our previous observations, where Nkd1 overexpression can antagonize endgonous Wnt8 signaling along the ventro-lateral domain at 50% epiboly, resulting in expanded expression of gsc, a dorsal organizer marker [12] (Figure 2F). This expansion must be corrected for later in development since we do not observe a dorsalized phenotype at 1 dpf (Figure 2B). This dichotomy in the effect of exogenous Nkd1 on endogenous or ectopic Wnt signaling suggests that the main effect of exogenous Nkd1 is to inhibit ectopic Wnt signaling.


Nkd1 functions as a passive antagonist of Wnt signaling.

Angonin D, Van Raay TJ - PLoS ONE (2013)

Nkd1 is sufficient to antagonize ectopic Wnt8a.Overexpression of Wnt8a (25pg) results in an eyeless phenotype that can be rescued by co-injection of nkd1 (A, B) which is quantified in (C). Numbers above each column represent n values. Overexpression of high Wnt8a (200pg) results in ectopic gsc expression along the ventral-lateral domain at 50% epiboly (E). Co-injection of high wnt8a with nkd1 mRNAs dramatically reduces the ectopic gsc expression, but leaves the putative endogenous gsc domain intact (F).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756965&req=5

pone-0074666-g002: Nkd1 is sufficient to antagonize ectopic Wnt8a.Overexpression of Wnt8a (25pg) results in an eyeless phenotype that can be rescued by co-injection of nkd1 (A, B) which is quantified in (C). Numbers above each column represent n values. Overexpression of high Wnt8a (200pg) results in ectopic gsc expression along the ventral-lateral domain at 50% epiboly (E). Co-injection of high wnt8a with nkd1 mRNAs dramatically reduces the ectopic gsc expression, but leaves the putative endogenous gsc domain intact (F).
Mentions: While Nkd1 has little apparent affect on overall development, it is still sufficient to antagonize Wnt signaling, although to varying degrees dependent on if it is endogenous or exogenous Wnt signaling (Figure 2). Overexpression of Wnt8 in zebrafish embryos results in an eyeless phenotype at 1 dpf, which is effectively rescued by Nkd1 and overall development appears normal, albeit with a smaller eye (Figure 2A–C). Similarly, Wnt8 can induce ectopic gsc expression at 50% epiboly, which is also effectively reduced by the addition of Nkd1 (Figure 2D–F). Note however, that there is also a subtle effect on endogenous Wnt signaling: expansion of dorsal gsc expression (Figure 2F). This is consistent with our previous observations, where Nkd1 overexpression can antagonize endgonous Wnt8 signaling along the ventro-lateral domain at 50% epiboly, resulting in expanded expression of gsc, a dorsal organizer marker [12] (Figure 2F). This expansion must be corrected for later in development since we do not observe a dorsalized phenotype at 1 dpf (Figure 2B). This dichotomy in the effect of exogenous Nkd1 on endogenous or ectopic Wnt signaling suggests that the main effect of exogenous Nkd1 is to inhibit ectopic Wnt signaling.

Bottom Line: There are several Wnt negative feedback regulators, which are active antagonists of Wnt signaling, but one feedback regulator, Nkd1, has reduced activity compared to other antagonists, yet is still a negative feedback regulator.While slb and tri mutants do not display alterations in canonical Wnt signaling, we found that they are hypersensitive to it.These results suggest that Nkd1 functions as a passive antagonist of Wnt signaling, functioning only when homeostatic levels of Wnt signaling have been breached or when Wnt signaling becomes destabilized.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.

ABSTRACT
Wnt signaling is involved in many aspects of development and in the homeostasis of stem cells. Its importance is underscored by the fact that misregulation of Wnt signaling has been implicated in numerous diseases, especially colorectal cancer. However, how Wnt signaling regulates itself is not well understood. There are several Wnt negative feedback regulators, which are active antagonists of Wnt signaling, but one feedback regulator, Nkd1, has reduced activity compared to other antagonists, yet is still a negative feedback regulator. Here we describe our efforts to understand the role of Nkd1 using Wnt signaling compromised zebrafish mutant lines. In several of these lines, Nkd1 function was not any more active than it was in wild type embryos. However, we found that Nkd1's ability to antagonize canonical Wnt/β-catenin signaling was enhanced in the Wnt/Planar Cell Polarity mutants silberblick (slb/wnt11) and trilobite (tri/vangl2). While slb and tri mutants do not display alterations in canonical Wnt signaling, we found that they are hypersensitive to it. Overexpression of the canonical Wnt/β-catenin ligand Wnt8a in slb or tri mutants resulted in dorsalized embryos, with tri mutants being much more sensitive to Wnt8a than slb mutants. Furthermore, the hyperdorsalization caused by Wnt8a in tri could be rescued by Nkd1. These results suggest that Nkd1 functions as a passive antagonist of Wnt signaling, functioning only when homeostatic levels of Wnt signaling have been breached or when Wnt signaling becomes destabilized.

Show MeSH
Related in: MedlinePlus