Mechanical cues regulate in vitro implantation of mouse embryos

Uterine mechanical properties, particularly tissue stiffness, are dynamically regulated during the embryo implantation window to ensure optimal mechanocompatibility. However, maternal aging and fibrotic pathologies, such as adenomyosis and intrauterine adhesions, disrupt this balance, leading to increased stromal stiffness due to abnormal extracellular matrix (ECM) deposition and crosslinking. In this study, we simulated various uterine environments in vitro by adjusting the mechanical cues, aiming to exploring embryonic mechanosensing and invasive capabilities during implantation. Our observations revealed that embryos cultured on softer substrates demonstrated enhanced developmental efficiency and exhibited distinct assembly morphologies compared to those on stiffer substrates. Using traction force microscopy (TFM), we quantified the traction forces exerted by embryos on soft substrates, noting a gradual increase in these forces before they stabilized within a specific range and displayed sustained fluctuations that were closely linked to cytoskeletal remodeling. We further identified that the traction force provided a real-time assessment of the developmental status of the embryo during implantation. Additionally, given that the mechanosensitive Yes-associated protein (YAP) differentially responds to substrate stiffness, we further investigated its pivotal role during early embryogenesis by RNA-seq. This research offers insights into mechanics-based interventions that could potentially enhance the outcomes in assisted reproductive technologies.