Nodal coordinates the anterior-posterior patterning of germ layers and induces head formation in zebrafish explants

Much progress has been made toward generating analogs of early embryos, such as gastruloids and embryoids, in vitro. However, methods for how to fully mimic the cell movements of gastrulation and coordinate germ-layer patterning to induce head formation are still lacking. Here, we show that a regional Nodal gradient applied to zebrafish animal pole explant can generate a structure that recapitulates the key cell movements of gastrulation. Using single-cell transcriptome and in situ hybridization analysis, we assess the dynamics of the cell fates and patterning of this structure. The mesendoderm differentiates into the anterior endoderm, prechordal plate, notochord, and tailbud-like cells along an anterior-posterior axis, and an anterior-posterior-patterned head-like structure (HLS) progressively forms during late gastrulation. Among 105 immediate Nodal targets, 14 genes contain axis-induction ability, and 5 of them induce a complete or partial head structure when overexpressed in the ventral side of zebrafish embryos. [Display omitted] •Nodal induces involution movements of mesendoderm in zebrafish embryonic explant•A-P-patterned endoderm, prechordal plate, notochord, and tailbud-like cells are specified•A head-like structure with A-P-patterned forebrain, midbrain, and hindbrain is formed•14 genes are identified downstream of Nodal and contain variable axis-induction ability Cheng et al. show that Nodal can robustly induce the development into an A-P-patterning contained head-like structure in the zebrafish embryonic explant by initiating a cascade of events, including cell differentiation and migration.