A quantitative investigation of shape change in epithelial monolayers

Epithelial tissues are one of the most abundant tissues in our body. They make up essential organs like the gut, heart and eyes. These organs take up their complex 3D shapes during normal development of the embryo. Our understanding of such large-scale 3D shape changes is limited mainly due to the technical difficulties of imaging and quantifying such developmental events. In this thesis, I study two events in which epithelial monolayers change their 3D shape. In both the projects, I use data from light-sheet microscopic images of developmental events. These data are provided by my collaborators. In this thesis, I further analyzed them using quantitative approaches and interpreted them using computational models. In the first project, I study a case of a developing tissue inside a rigid confinement. A perfect model system for this is the Drosophila embryo which consists of an epithelial monolayer (blastoderm) inside a rigid shell (vitelline membrane). During gastrulation, the blastoderm is under compressional stresses due to tissue proliferation and compression from the germband extension. During this time, an invagination separating the future head and the trunk region appears. This is known as the cephalic furrow (CF). As the CF disappears after some time, its relevance in the normal development of the embryo is unclear. To understand its role, my collaborators image the blastoderm in mutant embryos which lack CF. These mutant embryos have either of the genes even-skipped (eve) or buttonhead (btd) knocked down. In the absence of CF, temporary ectopic folds appear in the blastoderm in locations which vary between embryos. Unlike the CF, ectopic folds appear suddenly and hence look like buckling events. I hypothesize that ectopic folds appear because of the compressive stresses generated in the blastoderm during the germband extension or by the compression of tissues that are adjacent to mitotic domains. Moreover, in normal embryos, CF, which is a controlled invagin