Dynamics of Inductive ERK Signaling in the Drosophila Embryo

Abstract

Summary Transient activation of the highly conserved extracellular signal regulated kinase (ERK) establishes precise patterns of cell fates in developing tissues. Quantitative parameters of these transients are essentially unknown, but a growing number of studies suggest that changes in these parameters can lead to a broad spectrum of developmental abnormalities. We provide a detailed quantitative picture of an ERK-dependent inductive signaling event in the early Drosophila embryo, an experimental system that offers unique opportunities for high-throughput studies of developmental signaling. Our analysis reveals a spatiotemporal pulse of ERK activation that is consistent with a model in which transient production of a short-ranged ligand feeds into a simple signal interpretation system. The pulse of ERK signaling acts as a switch in controlling the expression of the ERK-target gene. The quantitative approach that led to this model, based on the integration of data from fixed embryos and live imaging, can be extended to other developmental systems patterned by transient inductive signals.

Synthesizing developmental trajectories

“…Our approach can also be extended using other semi-supervised learning methods [25], if the dimensionality of the intrinsic geometry is greater than one or if there is no unique common channel among all experiments. Most of the previous attempts to accomplishing this task explored specific features of developmental systems, such as the expression level of a particular gene, and used a discrete number of temporal classes, usually defined in ad hoc way [16,26]. Our approach reconstructs continuous time dynamics and relies on the intrinsic geometry of multidimensional datasets.…”

“…Stained embryos were imaged using Nikon A1-RS confocal microscope with a 60x Plan-Apo oil objective. Embryos were mounted in a microfluidic device for end-on imaging, as described previously [16,38]. The first dataset contains 108 images stained with rabbit antidpERK and rat anti-Twist antibodies.…”

“…The problem can be illustrated by an imaging dataset from the early Drosophila embryo (Fig 1A and 1B), a model system in which a graded profile of the nuclear localization of transcription factor Dorsal (Dl) establishes the dorsoventral (DV) stripes of gene expression that control cell fates and tissue deformations [13][14][15]. Current mechanisms of the DV patterning system invoke multiple state variables, such as the levels of gene expression and protein phosphorylation [16] (Fig 1C). These mechanisms were elucidated in studies that reveal only a small subset of the full state space, most commonly 2-3 variables per experiment.…”

New Twists in Drosophila Cell Signaling

“…In this case, transient production of a short-range ligand leads to a simple signal interpretation system, where a pulse of a given threshold is sufficient to induce the target gene. This hypothesis could be tested in a mutant background where the rate of activation is reduced, and induction of the target gene is indeed delayed until the same critical active MAPK threshold is reached (16).…”

The complexities and versatility of the RAS-to-ERK signalling system in normal and cancer cells

“…Coupled appropriately with negative and positive feedback, ultrasensitivity brings about complex dynamics, such as oscillations and bistability [5,10] believed to drive proliferation and differentiation, respectively [11,12]. Many dynamic models of ERK signalling have been developed [3,5,[13][14][15][16], lately moving to the single-cell level and trying to explain the response variability in cell populations [17], or including thermodynamic aspects in order to explain the paradoxical activation of RAF in response to inhibitors [18]. Yet, current models still lack many biological and pathophysiological aspects of RAS signalling.…”