Wingless secretion requires endosome-to-Golgi retrieval of

Wntless/Evi/Sprinter by the retromer complex

Presented by: Lecturer:

Lidija Berke Dr. Madelon Maurice

Renske Bolder

Liliana Joachín

October 9, 2008

Overview

Introduction

Experimental work Results Conclusions

General conclusions Final model for Wnt

secretion

IntroductionWnt proteins

Family of secreted glycoproteins (highly conserved).

Act as signaling molecules, local mediators and morphogens.

Regulate cell-to-cell interaction during embryogenesis.

Examples: Wingless, Hedgehog.

IntroductionDrosophila imaginal disc

Group of cells that are set aside, apparently undifferenciated in the Drosophila embryo and which will develop into an adult structure, e.g eye, leg, wing.

IntroductionSignal proteins in the wing imaginal disc

Hedgehog Posterior expression Short-range signal

Wingless

Ventral

Dorsal

Hedgehog

Anterior Posterior

Wingless Dorso-ventral action Long-range signal

IntroductionRetromer complex

Multiprotein complex that assembles on endosomes and form vesicles that return cargos to the Golgi apparatus.

It is formed only when:

It can bind to the cytoplasmic tails of the cargo (Vps35).

It can interact directly with a curved phospholipid bilayer.

It can bind to a specific phosphorilated PI lipid.

IntroductionPrevious findings about Wnt

Wnts undergo up to two lipid modifications Affect trafficking and spreading along epithelia. Hypothesis: They are transported by lipoprotein particles which

would shield lipid moieties, reducing membrane anchoring.

EGL-20 (a C. elegans Wnt) Its long-range action is impaired in retromer-deficient worms. Hypothesis: A retromer-dependent process might be required for

Wnt-producing cells to package Wnts into lipoprotein particles.

Research question

Is the retromer involved in Wingless secretion?

Important note

Wingless ---- Wingless (Wg)

Wntless ---- Wls/Evi (Wls)

Experimental work Loss of Vps35 affects the spread of Wingless

Generation of Drosophila mutants (deficient in Vps35)

Results: Melanotic tumors Wingless accumulation Incomplete wings

Conclusion:

Wingless trafficking might be affected in absence of Vps35 activity

Experimental work Loss of Vps35 affects the spread of Wingless

Mutation: posterior compartment deficient in Vps35

Results: Concentration of Wingless Wingless spreading reduced Reduction in extracellullar

Wingless

Conclusion:

In the absence of retromer function, progression of Wingless along the secretory pathway becomes blocked or impaired.

Experimental work Effects on short or long range wingless signaling

Senseless Distalless

Conclusion:

Vps35 has an important role in short range Wingless signalling

Experimental work Is vps35 also involved in Hedgehog secretion?

Hedgehog Wingless Patched

Conclusion:

Vps35 is required for a specific step in the secretion of Wingless

Experimental work Overexpression of Wls/Evi

Conclusion:

Overexpression of Wls/Evi rescues the wingless secretion phenotype of Vps35

Experimental work Stability of Wls/Evi

HEK293 cells

Conclusion:

Stability of Wls/Evi is reduced in the absence of Vps35 activity

Experimental work What happens after internalization of Wls/Evi in

the absence of retromer?

Conclusion:

In the absence of retromer function, Wls/Evi is diverted to MVBs.

Experimental work Physical interactions between retromer

components and Wls/Evi

Conclusion:

hWls/Evi forms a a complex with retromer components.

Experimental workTracking internalized Wls/Evi

Conclusions:Wls/Evi undergoes retrograde transport to the Golgi in a retromer dependent manner.

General conclusions Schematic representation of the role

of Wls/Evi in Wingless secretion

?