Symmetry breaking and germ layer emergence through optogenetic Wnt activation in gastruloids
Human gastrulation is a dynamic, complex, and poorly understood process. Starting from a seemingly homogenous population, cell and tissue organization during this process establishes the 3D organismal body plan. However, due to technical and ethical limitations, mechanisms of human gastrulation are largely unexplored. For example, it is generally unclear whether a spatially ordered, external cue is necessary for patterning, or whether the epiblast harbors the innate ability to differentiate and self-organize in the absence of asymmetric cues. Human pluripotent stem cells (hPSCs) fortunately offer the potential to model gastrulation, most notably through generation of 3D “gastruloids”. Here we use optogenetic control of Wnt signaling to establish a 3D hPSC gastruloid model and demonstrate the spatially-ordered emergence of the three germ layer lineages in the absence of exogenous asymmetrical cues. Overall design: scRNA-seq was performed on the 10X Genomics Chromium platform using the V3.1 3' chemistry, sequencing was done on a Novaseq 6000 paired end reads with depth aimed for 50k reads per cell.