The gradient of Gurken, a long-range morphogen, is directly regulated by Cbl-mediated endocytosis
2008
The asymmetric localization of gurken mRNA and post-translational
sorting mechanisms are responsible for the polar distribution of Gurken
protein in Drosophila . However, endocytosis of Egfr, the receptor for
Gurken in the follicle cells, also plays a role in shaping the extracellular
gradient of the Gurken morphogen. Previously, we have found that mutation in
the Cbl gene caused elevated Egfr signaling along the dorsoventral
axis, and resulted in dorsalization phenotypes in embryos and egg shells.
Here, we report that overexpression of the Cbl long isoform significantly
changed Gurken distribution. Using an HRP-Gurken fusion protein, we
demonstrate that internalization of the Gurken-Egfr complex depends on the
activity of Cbl . Increased levels of CblL promote the internalization
of this complex, leading to the reduction of free ligands. The Gurken-Egfr
complex trafficks through the Rab5/Rab7 associated endocytic pathway to the
lysosomal degradation compartment for signaling termination. We observe
endocytic Gurken not only in the dorsal but also in the ventral follicle
cells, which is, to our knowledge, the first visualization of Gurken on the
ventral side of egg chambers. Our results show that Gurken travels towards the
lateral/posterior of the egg chamber in the absence of Cbl ,
suggesting that Cbl actively regulates Gurken distribution through
promoting endocytosis and subsequent degradation.
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