Figure 1: Cross-section of a Drosophila embryo during late cellularisation (left panel) and ventral furrow formation (right panel) stained with antibodies against b-catenin (red), Notch (green) and Delta (blue). Embryos are oriented with the ventral side facing down and dorsal up. Cells on the ventral side are elongated along the apico-basal axis (left panel arrowhead) compared to their dorso-lateral neighbours. Endocytosis of Notch and Delta is specifically up-regulated in ventral cells during invagination.
Figure 2: Application of TIRF-M imaging to early Drosophila embryo allowed uncovering a prominent endocytic pathway controlling the morphology of the apical surface during epithelial development. Rab5 endosomes (purple), plasma membrane (green).
Cell shape changes are of fundamental importance during embryonic development – how cells form and change shape during morphogenesis are the key questions addressed by the De Renzis group.
Previous and current research
Tissue morphogenesis is triggered by shape changes in single cells or groups of cells. This remodelling depends on a complex interaction between cortical forces exerted by the actin cytoskeleton and membrane homeostasis (i.e. vesicular trafficking and lipid metabolism). We want to understand how membrane trafficking and cytoskeletal dynamics are regulated during morphogenesis and how this, in turn, impacts on specific cell and tissue behaviour. To this end, we combine high-resolution imaging methods with genetics and biochemistry using the early Drosophila embryo as model system (see figure 1 and video).
We have recently developed a modified form of total internal reflection fluorescence (TIRF) microscopy to follow apical surface dynamics in live embryos with unprecedented spatio-temporal resolution. Using this approach we have identified a novel endocytic pathway controlling the morphology of the apical surface during epithelial morphogenesis (figure 2), thus demonstrating for the first time that endocytosis directly controls cell and tissue shape. We are now using similar high-resolution imaging methods in combination with electron tomography to study the involvement of endocytosis in the regulation of cell signalling and membrane remodelling during tissue morphogenesis.
We are also interested in characterising the impact of lipid metabolism during morphogenesis. Using a chemical genetic approach we uncovered an exciting link between so-called ‘lipid induced phenotypes’ and developmental gene activities underlying the regulation of cell and tissue shape.
Finally, we are developing new optogenetic tools to control protein activity with light during tissue morphogenesis with high spatio-temporal precision.
Future projects and goals
Using a combination of imaging, genetics and optogenetic approaches we wish to elucidate how machineries controlling intracellular trafficking re-organise during differentiation and how this in turn impacts on global changes in tissue morphology.
Video: Plasma membrane dynamics during cell and tissue morphogenesis in an early Drosophila embryo imaged by two-photon microscopy.