The goal of our group is to understand how cell-cell communication controls the differentiation of diverse cell types. We exploit the accessibility of embryonic stem cells to measure and manipulate the dynamics of these processes in single live cells. Our main focus is on the role of the fibroblast growth factor (FGF) signaling system, a central signaling conduit involved in the differentiation of almost all cell types of the early mammalian embryo. We could show that cell-cell communication via FGF establishes and maintains robust and reproducible proportions of differentiated cell types. This requires cells to sense FGF levels, transmit this information inside the cell, and translate it into graded transcriptional responses. Our current goal is to explore the molecular mechanisms underlying these cellular information processing capabilities. We are also interested understanding how species-specific timescales of cell differentiation are emerge at a molecular and cellular level.