Initial Luminally Deposited FGF4 Critically Influences Blastocyst Patterning

Abstract: Luminogenesis, the formation of a fluid-filled cavity (lumen), is an essential process in early mammalian embryonic development, coinciding with the second cell-fate decision that differentiates the inner-cell-mass (ICM) into epiblast (EPI) and primitive endoderm (PRE) tissues. Based on experiments, the blastocyst lumen is hypothesized to influence EPI-PRE tissue specification, but its particular functional role remains theoretically underexplored. In this study, we extended our stochastic ICM differentiation model to incorporate both the blastocyst lumen (blastocoel) and the trophectoderm (TE) as adjacent compartments where the primary signaling protein (FGF4) for EPI-PRE differentiation can diffuse, degrade, or accumulate. This extended ICM model allows for a spatially resolved analysis of EPI-PRE lineage proportioning under the influence of luminally deposited FGF4 molecules. Our results reveal that the blastocoel acts as a localized signaling source, while the TE functions as an embryo-wide signaling sink, guiding cell-fate decisions within the ICM. A critical determinant of the ideal target system behavior is the initial amount of luminally deposited FGF4, which is required to recapitulate the correct spatio-temporal patterning of EPI and PRE (blastocyst) cell lineages. Notably, this requirement is independent of ICM population size and shape, highlighting the robustness of the FGF4 signaling process. Our study also underscores the potential of integrating single-cell gene expression and cell-cell communication dynamics simulations with tissue-level morphogenesis representations. By combining spatial-stochastic modeling with agent-based frameworks, we could enhance the exploration of the intricate interplay between gene regulation, signaling, and morphogenetic processes that govern early embryonic development.