Control of gastruloid patterning and morphogenesis by the Erk and Akt signaling pathways

Fibroblast growth factor (FGF) dependent elongation along an anterior-posterior (A-P) axis is a conserved feature of vertebrate embryogenesis. A-P axis elongation can also be reproduced in 3D cell culture models termed gastruloids, enabling dissection of this process in a controlled, minimal context. Here, we set out to determine how gastruloid posterior elongation depends on the Erk and Akt pathways, canonical downstream effectors of FGF signaling. We find that gastruloids exhibit reproducible posterior-to-anterior gradients in Erk and Akt phosphorylation that are generated independently and correlate with distinct zones of tissue movement, cell proliferation, and expression of cell motility and adhesion regulators. Pharmacological inhibition of FGFR, Erk, or Akt signaling impairs gastruloid elongation, and quantification of signaling gradients reveals how these patterns interact and scale with A-P axis length. Using global inhibitors and activators of each pathway, we find that a gradient of Ras/Erk signaling is required for the establishment of appropriately localized domains of E-cadherin, Snail, and Brachyury expression, whereas perturbing PI3K/Akt signaling alters proliferation but not patterning. Taken together, our data demonstrate that graded PI3K/Akt and Ras/Erk signaling provide spatial information to control proliferation and cell-cell adhesion during gastruloid elongation.