Regulation of actin, microtubules and focal adhesions during cell division : a specific role for GAS2-like proteins

My thesis, written in an alternative format, consists of three manuscripts. The first one is published in Journal of Cell Science and is entitled "GAS2-like proteins mediate communication between microtubules and actin through interaction with end-binding (EB) proteins." This article describes the mechanisms of how members of the GAS2 family of proteins mediate the crosstalk between actin and microtubules (MTs). We show that in particular GAS2-like 1 (G2L1) and GAS2-like 2 (G2L2) coordinate this cross-communication, as their exogenous expression leads to the stabilisation of MTs and guidance along actin stress fibres. We found that the association of GAS2-like members with MTs is mediated through their binding to EB proteins. The second article is a follow up story of the first article, in which we further elucidate the role of GAS2-like proteins during cell division. We show that G2L1 localises to the mitotic spindle and cleavage furrow during cell division. G2L1 knockdown leads to reduced cell division rates, multinucleation and nuclear deformation. As for MT guidance along actin filaments, we demonstrate that the binding of G2L1 to EB proteins plays an important role in cell division. Although overexpression of G2L1 had no effect, the expression of a mutant that blocks the association with EB proteins phenocopies the knockdown effect of G2L1 on cell division. Actin and MTs undergo major reorganisation during cell division. This reorganisation involves the fast remodelling of focal adhesions (FAs) but the mechanisms of this remodelling were not clear. In the third paper we demonstrate that the majority of FAs disassemble shortly before cell division and reassemble in newly formed daughter cells during cytokinesis. Interestingly, our data suggest that the regulation of FA disassembly during cell division differs from the disassembly processes during cell migration. While in migrating cells FAs can be stabilised by the expression of constitutively active vinculin (vinT12, known to circumvent the requirement forces for FA stability), this was not case for FAs during cell division. Further experiments using inhibitors suggested that calpain-driven cleavage of FA components but not endocytosis play a key role in FA disassembly during cell division. Altogether, the three manuscripts provide insight into important molecular aspects involved in the regulation of cell cytoskeletal networks and cell adhesion during cell division.