Self-organised symmetry breaking in zebrafish reveals feedback from morphogenesis to pattern formation

A fundamental question in developmental biology is how the early embryo breaks initial symmetry to establish the spatial coordinate system later important for the organisation of the embryonic body plan. In zebrafish, this depends on the inheritance of maternal mRNAs, cortical rotation to generate a dorsal pole of beta-catenin activity, and the release of Nodal signals from the yolk syncytial layer. How robust this mechanism is to alteration in the spatial positioning of embryonic cells in unknown. To investigate this, embryonic cells were explanted at the 256 cell stage and cultured in a minimal medium. Despite extensive cell mixing, they elongate, form distinct germ layers and an organiser-like domain with spatially organised neural tissue. This elongation has been shown to be the driving force which separates the anterior BMP from the posterior Wnt/TCF activity domain. Blocking of PCP-dependent convergence and extension disrupts this separation of the opposing domains and therefore prevents proper anterior posterior patterning of neural tissues. These results together suggest that morphogenesis plays a causal role in the establishment of morphogen gradients and pattern formation during zebrafish gastrulation.