Title: Regulation of cell shape by the cytoskeleton during tissue morphogenesis
Funder: Medical Research Council

Abstract: Epithelia constitute one of the major tissue types in all animals and form the basic building blocks of tubular organs in both vertebrates and invertebrates. Simple epithelial sheets are also the basic starting point in the development of most animals. We want to dissect how simple epithelial sheets deform in a highly concerted manner to turn into complex tubular tissue shapes. We use the formation of the tubes of the salivary glands in the Drosophila embryos as our main model system, but have also begun to compare our findings to the related process of budding morphogenesis in embryonic mouse lungs. Coordinated changes in the shape of many neighbouring cells, as well as cell rearrangements are the major drivers of tissue formation. Cell shape changes are driven by the intracellular cytoskeleton. We have in the past shown how crosstalk between the actomyosin cytoskeleton and microtubules is crucial to maintain a pool of actomyosin that drives apical constriction of cells during tissue bending. Coordination between cytoskeletal responses between neighbouring cells allows concerted tissue-scale changes in shape, often mediated through cell-cell adhesion receptors. We discovered that the apical polarity protein Crumbs, through newly identified homophilic interactions of its extracellular domain, can determine where a multicellular actomyosin cable is formed. The study of epithelial morphogenesis over the last decade has mostly focussed on events within the most apical portion of the cells. Our previous analysis of microtubule-actomyosin interactions and interdependence in the placode have clearly shown that structures that span the whole length of the cells, the longitudinal microtubules bundles, can have profound effects on events within the apical surface, the medial actomyosin contractions, and thus the whole cell volume and events within need to be studied. We now want to follow on from this analysis to address what happens in the remaining 90% volume of these epithelial cells during tube formation. We plan to dissect the control of cell shape changes during tissue morphogenesis by addressing questions at different scales and integrating the information gathered at each scale: 1) At the molecular level, we will analyse how responses of different cytoskeletal systems are coordinated during cell shape changes. In particular we will analyse how the microtubule cytoskeleton influences the actomyosin cytoskeleton and what the role of cytolinker proteins is in this process. 2) At the cellular level, we will dissect how cell-cell adhesion systems, in particular Crumbs homophilic interactions, impact on the intracellular actomyosin cytoskeleton and how cytoskeletal responses are coupled between cells, such as for instance during the assembly of multicellular actomyosin cables. 3) At the tissue level, we will segment and track epithelial cells in 3D over time, to understand the contribution of different cell behaviours to morphogenesis and also to uncover novel cell behaviours that drive shape changes at the tissue scale. We propose that the combination of approaches detailed above will give us a very detailed understanding of the cellular events that drive tube formation at the tissue level. The mutant analysis as well as the search for molecular factors driving these cellular behaviours will allow us to extend the understanding of epithelial morphogenesis from its current apical-centric view to a true 4D appreciation.


Research activity codes: 1.1 NORMAL BIOLOGICAL DEVELOPMENT AND FUNCTIONING
Health categories: GENERIC HEALTH RELEVANCE