INVESTIGATE THE CHARACTERISTIC SADDLE POINT DURING ZEBRAFISH GASTRULATION

Abstract

Morphogenetic movement is an emergent property from coordinated cell movement and is essential for morphogenesis. In developing embryos, the morphogenetic movement is guided by morphogen gradients, a group of small molecules which affect cellular activities including cell migration, division and differentiation. Therefore, the morphogen gradients determine the long-range biochemical order of morphogenesis. Increasing evidence over the last decade suggests that biochemical-mechanical coupling should exist across all scales. However, the mechanical counterpart of morphogen gradients remains elusive. In my thesis, I tried to address this problem by establishing the coarse-grained biophysical field corresponding to the biochemical field in the context of zebrafish gastrulation. These included an attempt to quantify the morphogenetic flow field, showing a characteristic pattern with 4 vortices and 2 saddle points over the embryo, followed by quantifying tissue deformation in the form of strain field. Moreover, enlightened by recent studies on the biological liquid crystals, I also investigated the nematic order in cell orientation during zebrafish gastrulation. I discovered that the nematic order together with the integer topological defects established a long-range biomechanical order over the embryo development, thereby providing a coarse-grained description of the long-range biochemical-mechanical coupling.