During morphogenesis individual cells self-assemble into complex tissues and organs with highly specialized forms and functions. Tissue morphogenesis is orchestrated via physical forces that are generated within cells by the cytoskeleton and that are transmitted through adhesion molecules within and between neighbouring cells. The best-studied cytoskeletal components are actin together with myosin, which forms contractile arrays across cells that are key constituents of different morphogenetic processes ranging from epithelial folding to cell intercalation and tissue convergence. Despite growing evidence that microtubules (MT) can act in a similar manner like actin to generate forces in cells, relatively little is known about how coupling of MT-based forces at epithelial intercellular junctions contributes to the cell mechanics (Figure 1). The ultimate goal of my lab is to unravel the role of the MT cytoskeleton as a force-generator during tissue development.
We are interested in the following questions that are central to understand the role of MT cytoskeleton in tissue morphogenesis:
(I) What are the structural and mechanical properties of non-centrosomal MTs in wing epithelial cells?
(II) How does MT mechanics contribute to shape changes and cell rearrangements during wing tissue remodeling?
(III) What is the molecular mechanism that integrates and coordinates MT forces across a tissue?
Mechanobiological quantification of microtubule mechanical properties during Drosophila wing morphogenesis
In order to reshape a tissue, force generation must exceed mechanical resistance, thus global patterns of force generation and tissue stiffness jointly dictate speed and direction of tissue rearrangements. The main focus of our studies is on the microtubule cytoskeleton. We investigate the mechanical and structural properties of apical non-centrosomal MTs nucleated at adherens junctions. For this we are using new optical and chemical tools (live imaging, caged MT drugs, laser ablation, FRAP, FRET based tension sensors) in conjunction with classical genetic approaches.
The quantitative data obtained with the mechanobiological approach are correlated with results obtained from quantitative image analysis of developing wing epithelium to study how mechanobiological properties of MTs contribute to cell shape changes and cell-cell contact remodeling.
Mechanical coupling of microtubules with adherens junctions
Tissue morphogenesis often requires collective cell behaviour. Only the integration of locally produced forces into a global tissue force pattern determines the resulting changes in cell and tissue shape. One of the principal signalling pathways coordinating individual cell dynamics to generate large tissue-scale rearrangements during morphogenesis is planar cell polarity (PCP). We recently showed that the PCP signalling pathway is capable of globally patterning MT cytoskeleton during epithelium development to coordinate local cell behaviours. This analysis and further examples from Drosophila, highlight the importance of MT patterning in promoting coordinated cell behaviour during tissue rearrangements. These studies suggest that apical non-centrosomal MTs nucleated at adherens junctions contribute to epithelial tissue morphogenesis via coordinated generation and integration of local, cell-based forces into a global tissue force pattern (collective mechanics).
To decipher the molecular mechanism that couples MTs with adherens junctions we are using proteomic approach in combination with Drosophila genetics to identify candidate proteins involved in association/nucleation of MTs with adherens junctions.