LAUSR

Extracellular Signal-Regulated Kinase (ERK) lies downstream of a core signalling cascade that controls all aspects of development and adult homeostasis. Recent developments have led to new tools to image and manipulate the pathway. However, visualising ERK activity in vivo with high temporal resolution remains a challenge in Drosophila. We adapted a kinase translocation reporter (KTR) for use in Drosophila, which shuttles out of the nucleus when phosphorylated by ERK. We show that ERK-KTR faithfully reports endogenous ERK signalling activity in developing and adult tissues, and that it responds to genetic perturbations upstream of ERK. Using ERK-KTR in time-lapse imaging, we made two novel observations: firstly, sustained hyperactivation of ERK by expression of dominant-active Epidermal Growth Factor Receptor raised the overall level but did not alter the kinetics of ERK activity; secondly, heterogeneity in ERK activity in retinal basal glia correlated with the direction of migration of individual cells. Our results show that KTR technology can be applied in Drosophila to monitor ERK activity in real-time and suggest that this modular tool can be further adapted to study other kinases. Summary Statement We describe a reporter to study the dynamics of ERK signalling in Drosophila, use it to measure signalling in individual cells over time, and monitor development.