Function of ebi and crumbs in growth control during drosophila organ development

Abstract

The dorsoventral (DV) boundary of wing imaginal disc is a signaling center for patterning and growth in Drosophila. The WD40 domain protein Ebi has been implicated in the regulation of Notch (N) signaling at the DV boundary (Marygold et al., 2011), but the underlying mechanism is unknown. Here we show that Ebi regulates wing growth by antagonizing the transmembrane protein Crumbs (Crb). We identified Ebi as a binding partner for the extracellular domain of Crb ($Crb^{ext}$). Physical interaction between Ebi and Crb is specifically mediated by the WD40 repeats 7-8 of Ebi and a laminin G domain of $Crb^{ext}$. Wing notching caused by reduced Ebi can be suppressed by decreasing the Crb function, indicating that Ebi is antagonistic to Crb. The WD40 repeats of Ebi are essential for binding Crb and antagonizing its function. Consistent with the antagonistic genetic interaction, Ebi knockdown in the DV boundary results in an upregulation of Crb protein level. We show that a fraction of Ebi and Crb proteins are localized together to the endosomal vesicles. Reduced Ebi leads to an accumulation of Crb with recycling endosomes. We reveal that Crb is ubiquitinated, and Ebi is required for the downregulation of Crb by ubiquitination. Taken together, we propose that the interplay of Crb expression and its downregulation by Ebi provides a feedback mechanism for regulated N signaling during wing development.