Dickkopf-1Dickkopf-1 regulates gastrulation regulates gastrulation

movements by coordinated modulationmovements by coordinated modulation

of Wnt/of Wnt/-catenin and Wnt/PCP activities,-catenin and Wnt/PCP activities,

through interaction with the Dally-likethrough interaction with the Dally-like

homolog homolog KnypekKnypek

2007, Genes & Dev

Luca Caneparo

Roles of Dkk1 in Gastrulation

During gastrulation, anterior territories (neural plate) keep their identities

by moving away from posteriorizing signals or inhibiting them

(Wilson S.W et al, 2004, Dev Biol)

Among the most studied posteriorizing signals are the Wnt molecules(Erter et al, 2001, Development)

Fight against Wnt!

(sFRP, WIF, Cerberus and Dkk)

Roles of Dkk1 in Gastrulation (continue)

In frog and fish, Dkk1 overexpression is able to anteriorize neural tissue

(Kazanskaya et al, 2000, Development)

The genetic knockout of the mouse dkk1 leads to the formation of headless

(Mukhopadhyay et al, 2001, Dev cell)

embryos due to lack of maintenance of anterior neural identity during gastrulation

But, mechanism by Dkk1 is yet to be unraveled

Gastrulation movement in zebrafish

Dkk1 is “Head inducer”

The morphant embryos show a severe reduction of forebrain territories

Dkk1 is important in rostal population of axial mesendoderm

Dkk1 antibody injected Xenopus embryo, gsc and shh (anterior endoderm marker)

in prechordal plate are down-regulated

(Kazanskaya et al, 2001, Development)

In the mouse dkk1/noggin double mutants, Hesx1 expression is

down-regulated in the presumptive prechordal plate

(del Barco et al, 2003, Genes & Development)

Absence of Dkk1 give the same effect in zebra fish?

Axial mesendoderm marker

Dkk1 regulates gastrulation movement

dorsal

- Significant reduction of gsc in dkk MO

- Position of the rostal-most limit of the

axial mesendoderm is different

Acceleration of Axial mesendoderm movement?

Dkk1

Dkk1 MO accelerates gastrulation movement

- The number of internalized cell/min

- The AP length of the clone - Distance of the rostal-most cell from the posterior margin

Dkk1 MO accelerates gastrulation movement

How does Dkk1 reduce gastrulation movement?

Two hypothesis

Dkk1

Canonical Wnt signaling block

Interact with LRP5/6 Interact with X

?

Gastrulation defect

Influence of Dkk1 on gastrulation is Wnt/-catenin independent

Clones are more dispersed

Don’t rescue the phenotype in Dkk1 MO

Knypek is a Dally-like heparan sulfate proteoglycan

(Dally)

In embryo lacking Knypek, mediolateral intercalations are impaired(Topczewski et al, 2001, Dev cell)

kny mutations exacerbate the CE defect of slb/Wnt11 mutants in a dose-dependent manner

(Lin F. et al, 2005, J cell biol)

And, Kny enhances Wnt11 signaling in overexpression experiments

Kny is a positive modulator of non-canonical Wnt signaling

If Dkk1 interacts with Kny ?

Dkk1 interacts with Knypek and it regulates propagation of Dkk1

Synergistic effect

Interact with Kny

Require Kny for its propagation

Kny-/- Kny-/- + Dkk1Wt+Dkk1

Propagation is necessary for dkk1 function

Dkk1 promotes Wnt / PCP pathwayactivin activin+Wnt8 activin+Dkk1

C&E defect

Dkk1 may act as a switch between the -catenin and PCP pathway

Phenocopy Dkk1 MO

Dkk1

Canonical Wnt signaling block

Interact with LRP5/6 Interact with knypek

Fine-tuned Gastrulation

Summary

Dkk1 propagation?

Internalization Wnt/PCP activation

Possible model