Kavli Affiliate: Eric D. Siggia
| Authors: Teresa Krammer, Hannah Taylor Stuart, Elena Gromberg, Keisuke Ishihara, Manuela Melchionda, Jingkui Wang, Elena Costantini, Stefanie Lehr, Dillon Cislo, Laura Arbanas, Alexandra Hoermann, Ralph Alexander Neumueller, Nicola Elvassore, Eric Siggia, James Briscoe, Anna Kicheva and Elly Margaret Tanaka
| Summary:
Organoids can undergo pattern formation by spontaneously forming spatially-localised signaling centers called organisers. Understanding how molecular pathways participate in this regulative process is a central challenge in biology. Here, we investigated self-organisation of a SHH-expressing floorplate in clonal neural tube organoids (NTOs). In NTOs, a pulse of retinoic acid (RA) applied at Day 2 triggers self-organisation of a FOXA2+ floorplate by Day 6. FOXA2 expression was initially spatially scattered before resolving into multiple clusters. These FOXA2+ clusters underwent competition and physical sorting, resulting in a stable ‘winning’ floorplate. We identified BMP signalling as a key governor of long-range cluster competition. The pathway displayed characteristics of a reaction-diffusion system: FOXA2+ clusters secreted BMP4 ligand suppressing FOXA2 in receiving cells, while simultaneously expressing the BMP-inhibitor NOGGIN to secure FOXA2+ cluster survival. Genetic deletion of Noggin perturbed the floorplate not only in vitro in NTOs but also in vivo at the mid-hindbrain region of mouse neural tube. These results demonstrate how the floorplate can form in the absence of its well-known inducer, the notochord and the in vivo relevance of these findings. Defining molecular pathways that govern organiser self-organization is an important step in harnessing the developmental plasticity of stem cells toward directed tissue engineering.