Signalling networks allow cells to integrate external and/or internal signals perceived during changes in their environment and to respond to them by altering transcriptional activity, metabolism, or other regulatory mechanisms. The accurate functioning of these networks is vital for adaptation and continued existence under unstable conditions, as well as for differentiation and cell fate. The concept of signalling networks has evolved from that of pathways. A signalling pathway could be defined as a cascade of events connecting input elements (in this review: the environmental stimuli, biotic and abiotic) to output elements (in this review: the responses). Until recently, such cascade was viewed in isolation as a simple chain of consecutive steps. However, recent research has focused on the divergence that is observed at several steps in a pathway and on the crosstalk, feedback, pleiotropy and redundancy between signalling pathways (Schwartz and Baron 1999; Klipp and Liebermeister 2006). It has been shown that signalling pathways interact with each other, forming a network and a full understanding of cell signalling can only be achieved by considering such signalling networks rather than the isolated pathways. In order to understand the multifaceted behavior of signalling networks, researchers have implemented computational modelling approaches, ranging from abstract models that emphasize some key features of signalling pathways to detailed models that describe the dynamics of specific pathways in specific organisms.
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