Abstract

To make and organize different tissues, cells decipher information from developmental signalling pathways. Transmitting this information accurately, so that cell-surface signals are translated into correct transcriptional responses, is of critical importance. For example, dosage and dynamics of Notch activity are fundamentally important for developmental decisions and tissue homeostasis and their mis-regulation underlies many diseases including cancers. To decipher the temporal, quantitative and mechanistic principles that govern how Notch activity is read by target enhancers in the living animal we image events in real time within living fly tissues. We have been addressing two fundamental questions. (i) what mechanisms and partners are required to transduce Notch signals at target genes? To investigate we have used live imaging and single particle tracking to measure the recruitment of transcription complexes to a Notch regulated gene locus in real time, starting with a Notch off condition and analysing the changes that take place when signalling is active and subsequently switched off. (ii) What are the real time dynamics of transcription in cells responding to Notch and how do these relate to developmental decisions being made. To answer this we are using the MS2 /MCP and PP7 /PCP systems to measure, live, transcription levels and dynamics from endogenous Notch-regulated genes on a cell-by-cell basis to see how they respond to signals and what the consequences are when we perturb different steps. Integrating the results from these two questions we are learning how enhancers decode levels and dynamics of Notch signalling to make key decisions.