The Trophoblast Compartment Helps Maintain Embryonic Pluripotency and Delays Differentiation towards Cardiomyocytes
Normal developmental progression relies on a close crosstalk between the embryonic and extraembryonic lineages in the pre- and peri-gastrulation conceptus. This has been demonstrated in the mouse where epiblast-derived FGF and NODAL signals are required to maintain a stem-like state in trophoblast cells of the extraembryonic ectoderm, while visceral endoderm signals are pivotal to pattern the anterior region of the epiblast. These developmental stages also coincide with the specification of the first heart precursors. Here, we established a robust differentiation protocol of mouse embryonic stem cells (ESCs) into cardiomyocytes that we used to test the impact of trophoblast on this key developmental process. Using trophoblast stem cells (TSCs) to produce trophoblast-conditioned medium (TCM), we show that TCM profoundly slows down the cardiomyocyte differentiation dynamics and specifically delays the emergence of cardiac mesoderm progenitors. TCM also strongly promotes the retention of pluripotency transcription factors. By applying TCM from various mutant TSCs, we further show that specifically those mutations that cause a trophoblast-mediated effect on early heart development alter the normal cardiomyocyte differentiation trajectory. Our approaches provide a meaningful deconstruction of the intricate crosstalk between the embryonic and the extraembryonic compartments. They demonstrate that trophoblast helps prolong a pluripotent state in embryonic cells by delaying early differentiative processes, likely through secretion of leukemia inhibitory factor (LIF). These data expand our knowledge of the multifaceted signalling interactions between distinct compartments of the early conceptus that ensure normal embryogenesis, insights that will also be of great importance for the field of synthetic embryo research. Overall design: RNA-seq of mouse EBs differnitated in standard base media or media conditioned by mTSCs for 4 or 8 days (N=3 for each condition at each timepoint). Every sample was sequenced in two lanes.