Seminar by Silas Boye Nissen

Cellular polarity is sufficient to enable robust morphological complexity in development

During in vitro organoid and in vivo organism development, the increasing morphological complexity seems to proceed through distinct stages of symmetry breaking. First, globular to spherical transition is driven by emergence of apical basal polarity. Next, emergence of axial symmetry - head-tail axis in primitive streak and transition from sheets to tubes during gastrulation and neurulation - coincides with the appearance of planar cell polarity. It is currently unclear how the changes cell-intrinsic properties are coordinated to produce specific morphological shapes. Are the observed cell rearrangements a result of global morphogen patterns instructing each and every cell, or can these dramatic changes be explained by a few localized organizing ques propagated by cell-cell neighbor interactions? To answer this question, we developed a computational tool to simulate thousands of polarized cells in 3D. With this tool and with only a few parameters, we are able to capture the main stages of sea urchin gastrulation and neural plate folding. We find that cellular polarity enables robust complex shapes and the details of the morphologies can be specified by initial and local boundary conditions alone and do not require global morphogens.