Clathrin heavy chain plays multiple roles in polarizing the Drosophila oocyte downstream of Bic-D

Abstract

Bicaudal-D (Bic-D), Egalitarian (Egl), microtubules and their motors form a transport machinery that localizes a remarkable diversity of mRNAs to specific cellular regions during oogenesis and embryogenesis. Bic-D family proteins also promote dynein-dependent transport of Golgi vesicles, lipid droplets, synaptic vesicles and nuclei. However, the transport of these different cargoes is still poorly understood. We searched for novel proteins that either mediate Bic-Ddependent transport processes or are transported by them. Clathrin heavy chain (Chc) co-immunopurifies with Bic-D in embryos and ovaries, and a fraction of Chc colocalizes with Bic-D. Both proteins control posterior patterning of the Drosophila oocyte and endocytosis. Although the role of Chc in endocytosis is well established, our results show that Bic-D is also needed for the elevated endocytic activity at the posterior of the oocyte. Apart from affecting endocytosis indirectly by its role in osk mRNA localization, Bic-D is also required to transport Chc mRNA into the oocyte and for transport and proper localization of Chc protein to the oocyte cortex, pointing to an additional, more direct role of Bic-D in the endocytic pathway. Furthermore, similar to Bic-D, Chc also contributes to proper localization of osk mRNA and to oocyte growth. However, in contrast to other endocytic components and factors of the endocytic recycling pathway, such as Rabenosyn-5 (Rbsn-5) and Rab11, Chc is needed during early stages of oogenesis (from stage 6 onwards) to localize osk mRNA correctly. Moreover, we also uncovered a novel, presumably endocytosis-independent, role of Chc in the establishment of microtubule polarity in stage 6 oocytes.

Efficient Endocytic Uptake and Maturation in Drosophila Oocytes Requires Dynamitin/p50

“…The function of Dynein in endocytic uptake likely involves efficient localization of the Clathrin complex at the oocyte cortex ( Figure 10M). This is consistent with recent findings of Vazquez-Pianzola et al who demonstrated a role for the Dynein adaptor BicD in the cortical localization of Chc (Vazquez-Pianzola et al 2014).…”

“…Consistent with published results, Clathrin heavy chain (Chc), Rab5, and Rab7 localized along the cortex in control oocytes ( Figure 2Q; data not shown) (Tanaka and Nakamura 2008;Vazquez-Pianzola et al 2014). In egg chambers expressing dmn shRNA-A, two phenotypes were observed.…”

“…In contrast to control oocytes, Dynein was completely delocalized from the cortex in egg cambers depleted of either Shibire or Rab5 (Figure 10,G and H;data not shown). While this article was in preparation, Vazquez-Pianzola et al demonstrated a role for Bicaudal-D (BicD) in the cortical localization of Chc (Vazquez-Pianzola et al 2014). BicD is an adaptor of the Dynein motor and has been shown to directly interact with Chc (Li et al 2010).…”

Multiple Roles for Egalitarian in Polarization of the Drosophila Egg Chamber

“…grk mRNA, and to a lesser extent, osk mRNA, were also enriched in Egl pellets ( Figure 1D). Thus, as observed in Drosophila embryos (Dienstbier et al 2009;Vazquez-Pianzola et al 2014), Egl associates with mRNAs that are destined for localization.…”

The temporally controlled expression of Drongo, the fruit fly homolog of AGFG1, is achieved in female germline cells via P-bodies and its localization requires functional Rab11

“…In Drosophila egg chambers, apart from its role in the formation of clathrincoated vesicles, Chc has been reported to play a role in the polarization of the microtubule network at stage 6. 54 Clc has been shown to direct endocytosis by providing direction for membrane internalization. 55 After stage 7, Drongo localizes mainly at the oocyte's cortex, where it shows significant overlap with Clc-GFP, concurrent with the activation of bulk endocytosis.…”