High-Precision cross-scale analysis of tissue

Wednesdays@NICO Seminar, Noon, February 17 2010, Chambers Hall, Lower Level

Prof. Matthias Kaschube, Department of Physics, Princeton University


During embryonic development, individual cell shape changes and movements collectively sculpt tis-sues into organs with precise forms and functions. These tasks require the orchestrated interplay of large collections of cells. We combine real-time imaging, quantitative image analysis, and physical modeling of Drosophila gastrulation to study the force-generating mechanisms that drive epithelial sheet bending and invagination during morphogenesis. We reveal a novel ‘ratchet’ mechanism for apical constriction in ventral furrow cells and show that apical constriction is pulsed, with phases of constriction interrupted by pauses in which the cell size is maintained. Actin-myosin network contractions on the apical cortex drive constriction. Our results contrast with the conventional model in which an actin-myosin purse-string causes continuous constriction. We find that the transcription factors twist and snail differentially regulate the separate phases of the contraction cycle, demonstrating how the activities of these genes are coordinated to produce shape changes in individual cells. To study how apical constriction is propagated towards the basal side of cells, we reconstruct and quantitatively characterize cell shapes in three dimen-sions. Furthermore, by tracking local groups of cells over time we study the effect of constriction pulses on neighboring cells in order to reveal cell-cell interactions that coordinate constriction among cells to realize morphogenetic changes on the tissue level.