Lumen expansion facilitates epiblast-primitive endoderm fate specification in the mouse blastocyst formation

Abstract

Mouse blastocyst formation involves lumen formation and cell fate specification. While many studies have investigated how the blastocyst cell lineages are specified through genetics and signaling, studies into the potential role of the fluid lumen have yet to be conducted. We discover that blastocyst fluid emerges by secretion of cytoplasmic vesicles to intercellular space in addition to trans-epithelial flow. We observe that the beginning of epiblast and primitive endoderm spatial segregation directly follows lumen coalescence. Notably, we show that perturbing lumen expansion by pharmacological and biophysical means impair the specification and spatial segregation of primitive endoderm cells within the blastocyst. Combined, our results suggest that blastocyst lumen expansion plays a critical role in guiding cell fate specification and positioning. As epithelial tissues typically form lumina, lumen expansion may provide a general mechanism of cell fate control in many tissues.

Brazil Nut Effect Drives Pattern Formation in Early Mammalian Embryos

“…When the energy of the cavity has accumulated to a certain extent, it may be released and converted in other forms, which affects the entire system. The function of cavity expansion in the lineage specification of PrE/EPI cells has also been observed in a recent study 21 . In our experiments, drug treatment of blastocysts has certain limitations in terms of gene expression, but we are more concerned about changes in physical factors.…”

“…It has been reported that during the development of blastocysts, PrE precursors move toward the ICM-cavity interface, whereas EPI cells retain inside the ICM compartment 19 . In our experiment, we visualized the migration of PrE precursors from stage E3.5 through time-lapse imaging of PrE-specific single-cell resolution reporter ( Pdgfra H2B-GFP/+ , 20 ) embryos (Figure 1a, b and Supplemental movie S1).…”

“…In our experiment, we visualized the migration of PrE precursors from stage E3.5 through time-lapse imaging of PrE-specific reporter ( Pdgfra H2B-GFP/+ , 22 ) embryos (Figure 1a, b and Supplemental movie S1). By analyzing the relative distance of the GFP-positive cells to the center of the ICM surface 21 (Figure 1c), we found that at the initial hours of observation, no significant migration of PrE precursors showed little migration; however, after 8.5 hrs (approximately stage E3.75), the distance of GFP-positive cells to the center of ICM surface was progressively reduced, indicating that the relative allocation of PrE precursors tended to approach the center of the ICM surface (Figure 1d and e). Concurrently, we found that at the beginning of observation, the cavity of the blastocyst continuously expanded, and after E3.75, the blastocoel began to display rhythmic vibration (Figure 1f, g and Supplemental movie S2), which was accompanied by the significant migration of PrE precursors (Figure 1d and e).…”