# Role of BicDR in bristle shaft construction and support of BicD functions

## TL;DR

This study explores how BicD and BicDR proteins help build bristles in fruit flies by organizing the cytoskeleton and transporting cargo.

## Contribution

The study reveals a specific role for BicDR in supporting BicD during bristle development and local cargo transport.

## Key findings

- BicD and BicDR help organize the actin cytoskeleton in bristle shafts.
- BicDR supports BicD in the transport of Rab6 and Spn-F proteins.
- EF1γ is identified as a potential cargo of BicD and BicDR in bristle construction.

## Abstract

Cell polarization requires asymmetric localization of numerous mRNAs, proteins and organelles. The movement of cargo towards the minus end of microtubules mostly depends on cytoplasmic dynein motors. In the dynein–dynactin–Bicaudal-D transport machinery, Bicaudal-D (BicD) links the cargo to the motor. Here, we focus on the role of Drosophila BicD-related (BicDR, CG32137) in the development of the long bristles. Together with BicD, it contributes to the organization and stability of the actin cytoskeleton in the not-yet-chitinized bristle shaft. BicD and BicDR also support the stable expression and distribution of Rab6 and Spn-F in the bristle shaft, including the distal tip localization of Spn-F, pointing to the role of microtubule-dependent vesicle trafficking for bristle construction. BicDR supports the function of BicD, and we discuss the hypothesis whereby BicDR might transport cargo more locally, with BicD transporting cargo over long distances, such as to the distal tip. We also identified embryonic proteins that interact with BicDR and appear to be BicDR cargo. For one of them, EF1γ (also known as eEF1γ), we show that the encoding gene EF1γ interacts with BicD and BicDR in the construction of the bristles.

Summary: Drosophila BicD and BicDR are needed for the elaboration of the F-actin bundles of macrochaetae and proper Rab6 and Spn-F expression. BicDR appears to support BicD in vesicle transport.