08-P013 Mercury (Drosophila Tubulin Binding Cofactor B) controls cell polarity through the stabilisation of the microtubule network

Abstract

In Drosophila, the polarity cues controlling the axis formation of the adult fly are asymmetrically distributed in the oocyte, a process depending on the microtubule (MT) network. In order to identify new genes controlling the oocyte polarity, a genetic screen after mutagenesis has been done in the laboratory. In one of the mutants identified, that we named mercury, the posterior determinant oskar mRNA and the nucleus were strongly mislocalised. In the Drosophila germline, the germ cells are surrounded by a monolayer of somatic epithelial cells called the follicle cells. In mercury mutant follicle cells, the apical localisation of Par3 and aPKC and the lateral localization of α-spectrin were strongly disrupted indicating a loss of polarity. The follicle cells also formed multilayers, a characteristic of mispolarised cells. We next mapped the mutation and identified the mutated gene as the homologous of mammalian Tubulin Binding Cofactor B (TBCB). Tubulin binding cofactors have been demonstrated to be necessary for the formation of the αβ-tubulin heterodimers and are therefore potential regulators of the αβ-tubulin pool and of the microtubule stability. In agreement with this, we found that, in mercury mutant oocytes and follicle cells, the microtubule network was strongly destabilised. As the establishment of polarity is a MT dependant process, the loss of polarity observed in mercury mutant cells is probably a consequence of the destabilization of the MT network. Finally, we found that total α- and β-tubulin protein decreased strongly in the mutant cells.