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

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.

Role of BicDR in bristle shaft construction, tracheal development, and support of BicD functions.

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, which function as multiprotein complexes. In the dynein/dynactin/Bicaudal-D (DDB) transport machinery, Bicaudal-D (BicD) links the cargo to the motor. Here we focus on the role of BicD-related (BicDR) and its contribution to microtubule-dependent transport processes. Drosophila BicDR is required for the normal development of bristles and dorsal trunk tracheae. Together with BicD, it contributes to the organization and stability of the actin cytoskeleton in the not-yet-chitinized bristle shaft and the localization of Spn-F and Rab6 at the distal tip. We show that BicDR supports the function of BicD in bristle development and our results suggest that BicDR transports cargo more locally whereas BicD is more responsible for delivering functional cargo over the long distance to the distal tip. We identified the proteins that interact with BicDR and appear to be BicDR cargo in embryonic tissues. For one of them, EF1γ, we showed that EF1γ genetically interacts with BicD and BicDR in the construction of the bristles.