Geometric and mechanical control of developmental Yap signaling

点击翻译按钮获取中文摘要

In order to build complex and structured tissues, organs and embryos during development, individual cells need to interpret their environment and acquire appropriate cell fates at the right place and time. Failure to do so can result in various developmental abnormalities or the emergence of cancer when cells become unresponsive to the stops and checks imposed by their environment. The preimplantation mouse embryo develops without any spatially pre-patterned information from the oocyte and without any external input, making it an ideal mammalian developmental system to address how cells interact with their surroundings to specify and maintain cell fates. The first cell fate decision is made in the context of a mere ball of cells. Cells allocated to the surface will acquire the trophectoderm fate, becoming the progenitors of the future placenta, and cells within the embryo will become the inner cell mass, giving rise to the embryo proper and extraembryonic membranes. Interpreting this positional information through the presence or absence of apico-basal polarity, which in turn dictates the activity of the conserved Hippo signaling pathway and the subcellular localization of its effector, Yes-associated protein (YAP), was shown to play a role in driving fate specific gene expression programs. However, YAP has been shown to be a key transducer of various mechanical inputs in other systems, including sensing cell shape, extracellular matrix stiffness or tensile forces transmitted by neighboring cells. Although mechanosensing has been proposed to occur during preimplantation development, it is unclear which mechanical inputs are interpreted and whether these directly influence YAP localization and thereby cell fate. Additionally, as most of our understanding of YAP regulation stems from the analysis of fixed samples, how mechanical and polarity cues regulate YAP localization dynamics is not known. Here we will use cutting-edge long term live imaging of endogenously tagged reporters of YAP and downstream lineage markers to simultaneously measure cell shape and position, YAP localization and cell fate specific transcription factor expression to reveal their joint dynamics. To probe the role of mechanical inputs and cell geometry in directing YAP localization, we use various mechanical perturbations coupled with live or single cell transcriptomic readouts. These perturbations include substituting cell-cell interactions normally experienced in the embryo with cell-mimetic biomaterials, which can be fine-tuned to precisely manipulate geometric and mechanical inputs a single cell receives; or applying different amounts of strain to cells to probe the effects experienced when the blastocoel cavity forms. Finally, by using Fluorescence Recovery after Photobleaching and protein stability measurements in live embryos, we will determine how polarity and mechanics regulate the kinetic behavior of YAP and how YAP activity dynamics is linked to cell fate acquisition and maintenance. This work will shed light on how a conserved signaling pathway operates to integrate multiple inputs coupling morphogenesis with robust acquisition of cell fate in the early mammalian embryo.