Figure 1.

Overview of the complementary approaches to study complexity in developmental biology

On the left, the reductionist top-down approach is shown; whole embryos are scaled down into component cells, and down to component molecules. On the right, the reconstructive bottom-up approach aims to build in vitro models from elementary components at different levels in the hierarchical scale. Reconstitution beginning from the cellular level would include organoids and embryo models, while reconstitution beginning from the molecular level would include the use of synthetic circuits for engineering developmental transitions and patterned assemblies. The two approaches represent a schematic guide and inform each other. For example, a basal understanding from top-down approaches is necessary to attempt reconstructive approaches. Reconstructive approaches can then, in themselves, help further understanding. While useful to think about these approaches as distinct, the two are not fully separable.