Abstract

Genetics and biochemistry have defined the components and wiring of the signaling pathways that pattern the embryo. Many of these pathways have the potential to behave as morphogens: in vitro experiments have clearly established that these molecules can dictate cell fate in a concentration dependent manner. How morphogens convey positional information in a developing embryo, where signal levels are changing with time, is less understood. Recently we showed that the evolutionarily conserved TGF β pathway responds transiently and adaptively to a step in ligand stimulation. In the first part of my talk I will present how using integrated microfluidic cell culture to stimulate the cells with well-defined temporal profile of morphogen (TGFβ) and timelapse microscopy to record their response in realtime, we demonstrated that the speed of ligand presentation has a key and previously unexpected influence on signaling outcomes. Slowly increasing the ligand concentration diminishes the response while well-spaced pulses of ligand combine additively resulting in greater pathway output than is possible with constant stimulation. Our results suggest that in an embryonic context, an adaptive pathway can naturally extract positional information as ligand spreads from a fixed source, thereby providing an alternative to the static morphogen model where the rate of change of ligand concentration, rather than its level, is the meaningful signal for patterning. In a second part of my talk, I will present how using adhesive micro-patterns as a tool to control Embryonic Stem Cells colony size and shape provides a very promising in vitro model system to study the spatial selforganization occurring during one of the first the pattering event in the embryo: the transition from pluripotency to the 3 germ layers.