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Abstract

The formation of the ventral furrow in the Drosophila embryo has served as one of the major paradigms for how large-scale morphogenetic events are initiated, controlled and mediated by cellular behavior. The furrow is formed by the inward folding of the mesoderm epithelium on the ventral side of the early embryo. While it is well established that the onset of gastrulation is initiated by the apical constriction of the central mesoderm cells (CM), a subpopulation about 8-10 rows wide, it has recently become clear that furrow internalization can only be completed with the cooperation of the lateral mesodermal (LM) cells, a subpopulation about 3-4 rows wide on each side of the mesoderm that, instead of constricting, expand their apical areas at the same time. In this thesis we have developed a method to reconstruct 3D cell volumes in the entire embryo to study the coordination of cells shape changes during ventral furrow formation. We find that the cell shape changes in LM cells are passive and depend on the forces generated during apical constriction in the CM cells. A twist induced gradient of molecular cascade leading to apical MyosinII recruitment in the mesoderm results into a ‘tug-ofwar’ between the adjacent cells. Due to high amount of apical MyosinII recruitment, the CM cells constrict stronger and causes the LM cells to expand apically.