Dissecting the dynamics of signaling events in the BMP, WNT, and NODAL cascade during self-organized fate patterning in human gastruloids

Abstract

During gastrulation, the pluripotent epiblast is patterned into the three germ layers, which form the embryo proper. This patterning requires a signaling cascade involving the BMP, WNT and NODAL pathways; however, how these pathways regulate one another in space and time to generate cell-fate patterns remains unknown. Using a human gastruloid model, we show that BMP signaling initiates a wave of WNT signaling, which, in turn, initiates a wave of NODAL signaling. While WNT propagation depends on continuous BMP activity, NODAL propagates independently of upstream signals. We further show that the duration of BMP signaling determines the position of mesodermal differentiation while WNT and NODAL synergize to achieve maximal differentiation. The waves of both WNT and NODAL signaling activity extend farther into the colony than mesodermal differentiation. Combining dynamic measurements of signaling activity with mathematical modeling revealed that the formation of signaling waves is inconsistent with WNT and NODAL forming a stable spatial pattern in signaling activities, and the final signaling state is spatially homogeneous. Thus, dynamic events in the BMP, WNT, and NODAL signaling cascade, in the absence of a signaling gradient, have the potential to mediate epiblast patterning.

Engineering Stem Cell-Derived Extracellular Matrices: Decellularization, Characterization, and Biological Function

“…11,12 Similarly, PSC proliferation and differentiation recapitulate embryonic tissue development and are accompanied by dynamic remodeling of ECMs and local gradients of morphogens. [13][14][15] Hence, ECM proteins and regulatory factors surrounding stem cells form a regulatory niche and play essential roles in modulating stem cell fate. 16,17 Understanding and recapitulating the characteristics of stem cell microenvironment should significantly improve our ability to control stem cell fate in tissue regeneration and cell therapy.…”

Gene regulatory network (GRN) embedded agents connect cellular decision making to human pluripotent stem cell derived germ layer-like pattern formation

“…Models that have previously tried to explain the emergence of germ-layer patterns have relied on gradients of individual signals including BMP4 (Etoc et al, 2016;Tewary et al, 2017), NODAL (Tewary et al, 2019), and WNT (Chhabra et al, 2019). We build on these models in three ways.…”

“…As we intended to create a minimal GRN that captured both the maintenance of pluripotency and exit to germ-layer states, we focused on a narrow set of genes, signals, and interactions for model development. For example, we set-aside NANOG due to its lineage restricted role in maintaining pluripotency (Wang et al, 2012) and NODAL signalling given that BMP & WNT pathways have been shown to successfully trigger exit from pluripotency to germ-layer fates (Tewary et al, 2017;Chhabra et al, 2019;Martyn et al, 2018). Similarly, other germ-layer fate associated TFs, such as EOMES, FOXA1, OTX2, were also not directly considered at this time.…”

“…The patterning signaling cascade has been extended to include a BMP → Wingless Integrated (WNT) → NODAL pathway hierarchy in hPSCs (Martyn et al, 2018). Evidence exists that this cascade evolves dynamically in space and time yielding neighbouring domains in a sequential manner (Chhabra et al, 2019;Tewary et al, 2019).…”

High-resolution transcriptional and morphogenetic profiling of cells from micropatterned human embryonic stem cell gastruloid cultures

“…The BMP, WNT and NODAL signaling cascade is important during mammalian gastrulation and gastruloid formation in micropattern (Chhabra et al, 2018;Martyn et al, 2018). Specifically, WNT and NODAL pathways synergize to instruct mesoderm differentiation in gastruloids, whereas changes in the duration of BMP signaling alter the position of mesodermal ring (Chhabra et al, 2018). Thus, the dynamic interplay of signaling pathways, such as the duration and timing, governs cell fate patterns in gastruloids.…”