Plasticity in the Macromolecular-Scale Causal Networks of Cell Migration

et al. (2014) Plasticity in the Macromolecular-Scale Causal Networks of Cell Migration. PLoS ONE 9(2): e90593. doi:10.1371/journal.pone.0090593 Plasticity in the Macromolecular-Scale Causal Networks of Cell Migration John G. Lock 0 Mehrdad Jafari Mamaghani 0 Hamdah Shafqat-Abbasi 0 Xiaowei Gong 0 Joanna Tyrcha 0 Staffan Stro mblad 0 Jung Weon Lee, Seoul National University, Republic of Korea 0 1 Center for Biosciences, Department of Biosciences and Nutrition, Karolinska Institutet, Huddinge, Sweden, 2 Division of Mathematical Statistics, Department of Mathematics, Stockholm University , Stockholm , Sweden Heterogeneous and dynamic single cell migration behaviours arise from a complex multi-scale signalling network comprising both molecular components and macromolecular modules, among which cell-matrix adhesions and F-actin directly mediate migration. To date, the global wiring architecture characterizing this network remains poorly defined. It is also unclear whether such a wiring pattern may be stable and generalizable to different conditions, or plastic and context dependent. Here, synchronous imaging-based quantification of migration system organization, represented by 87 morphological and dynamic macromolecular module features, and migration system behaviour, i.e., migration speed, facilitated Granger causality analysis. We thereby leveraged natural cellular heterogeneity to begin mapping the directionally specific causal wiring between organizational and behavioural features of the cell migration system. This represents an important advance on commonly used correlative analyses that do not resolve causal directionality. We identified organizational features such as adhesion stability and adhesion F-actin content that, as anticipated, causally influenced cell migration speed. Strikingly, we also found that cell speed can exert causal influence over organizational features, including cell shape and adhesion complex location, thus revealing causality in directions contradictory to previous expectations. Importantly, by comparing unperturbed and signalling-modulated cells, we provide proof-of-principle that causal interaction patterns are in fact plastic and context dependent, rather than stable and generalizable. - Funding: This work was supported by grants to SS from the EU-FP7 Systems Microscopy NoE (Grant No. HEALTH-F4-2010-258068), the Centre for Biosciences at KI, the Swedish Research Council and the Swedish Cancer Society. Imaging occurred at the live cell-imaging unit at the Department of Biosciences and Nutrition at KI, supported by grants from the Knut and Alice Wallenberg Foundation, the Swedish Research Council and the Centre for Biosciences at KI. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. . These authors contributed equally to this work. A key challenge in biology is to understand how information is coordinated globally within cells to generate and control complex cellular processes, such as cell migration. Succinctly, what is the wiring pattern of regulation that governs a particular cell behavior? Importantly, this raises a second fundamental question that we seek to address herein: is the wiring pattern for a particular process stable and generalizable, or, plastic and contextually dependent? The answer to this second question has important implications for our understanding of both complex biological processes and the design of the experimental strategies to address them. Cell migration is a process of vital importance in numerous physiological and pathological processes including cancer cell metastasis [1]. Cell migration is indeed a highly complex cellular process, arising from a large, self-organizing molecular network to produce behaviors that are dynamic, heterogeneous and adaptable [2]. The dynamism of these behaviors suggests that underlying plasticity in the wiring of the cell migration system might be both more likely and more readily detectable than in relatively constrained cellular phenomena. Thus cell migration provides an appropriate framework within which to assess both the structure and potential plasticity of cellular wiring patterns. Cell migration is the product of interactions and interdependencies operating across molecular, macromolecular, and cellular scales (see Figure 1). As noted above, a huge diversity of components comprise the network underlying migration at the molecular scale (Figure 1 A) [38]. Such large-scale molecular networks tend to be arranged into hierarchically nested assemblages or modules [9,10]. These macromolecular modules often represent functional units with distinct roles whose interactions ultimately produce single cell migration behaviors (Figure 1 B and C). To understand how cell migration behaviors derive from molecular-, macromolecular- and cellular-scale organization, it is desirable to characterize all scales simultaneously and with sufficient spatiotemporal resolution to delineate functional relationships between features at any scale. Live cell fluorescence imaging provides the spatiotemporal resolution to track individual migrating cells while concurrently monitoring features of their molecular- and macromolecular-scale organization. Unfortunately, such imaging does not permit us to directly observe the complete state of molecular networks underlying cell migration (Figure 1 D), and as a consequence we cannot synchronously and globally observe how molecular signaling pathways are integrated. The canonical means to overcome such limitations on direct observation have been to assemble, piecewise, the functional contributions and relations of individual molecular components through perturbation-based epistasis analyses. Yet, despite facilitating great progress, reductionist perturbation-based approaches alone may be insufficient to provide a systems-level understanding, particularly of dynamic, heterogeneous processes with potentially emergent properties [1114]. In particular, there are substantial risks of misattribution associated with the inference of molecular function based on targeted component perturbation [15]. Thus, there remain significant limitations on our ability to spatiotemporally resolve, either through direct observation or perturbationbased inference, how global information processing at the molecular scale gives rise to migratory behaviors. Given the modularity in molecular network structure noted above, an alternative strategy is to analyze the state and interactions of functional macromolecular modules within migrating cells. This provides a means to coarse-grain the overwhelming molecular-scale complexity to a level that is tractable with imaging-based approaches, as recently demonstrated [16,17] (Figure 1 A and B). However, even given such coarse-graining, it remains necessary to focus on a subset of (...truncated)