A Conserved Di-Basic Motif of Drosophila Crumbs Contributes to Efficient ER Export

Area of Science:

• Cell Biology
• Molecular Biology
• Developmental Biology

Background:

• Crumbs protein is essential for maintaining epithelial cell polarity in Drosophila.
• The precise mechanisms regulating Crumbs protein trafficking to the plasma membrane are not fully understood.

Purpose of the Study:

• To identify regulators of Crumbs protein trafficking.
• To elucidate the molecular mechanisms controlling Crumbs localization at the plasma membrane.

Main Methods:

• Genetic screening in Drosophila embryos to identify trafficking regulators.
• Pulse-chase assays in Drosophila Schneider cells.
• Analysis of protein transport kinetics using Endoglycosidase H resistance.

Main Results:

• Sar1, a component of COPII vesicles, was identified as a regulator of Crumbs trafficking.
• A di-basic RNKR motif in Crumbs was found to mediate interaction with Sar1 and promote ER export.
• This motif is crucial for Crumbs delivery to the plasma membrane in epithelial cells.

Conclusions:

• The RNKR motif serves as an ER export signal for the type I transmembrane protein Crumbs.
• This study reveals a novel role for di-basic motifs in regulating ER exit of plasma membrane proteins in metazoans.