Abstract. Probabilistic model checking is a formal verification technique that has been successfully applied to the analysis of systems from a broad range of domains, including security and communication protocols, distributed algorithms and power management. In this paper we illustrate its applicability to a complex biological system: the FGF (Fibroblast Growth Factor) signalling pathway. We give a detailed description of how this case study can be modelled in the probabilistic model checker PRISM, discussing some of the issues that arise in doing so, and show how we can thus examine a rich selection of quantitative properties of this model. We present experimental results for the case study under several different scenarios and provide a detailed analysis, illustrating how this approach can be used to yield a better understanding of the dynamics of the pathway. 1

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The Sprouty (Spry) family of proteins represents endogenous regulators of downstream signaling pathways induced by receptor tyrosine kinases (RTKs). Using real time PCR, we detect a significant increase in the expression of Spry4 mRNA in response to NGF, indicating that Spry4 could modulate intracellular signaling pathways and biological processes induced by NGF and its receptor TrkA. In this work, we demonstrate that overexpression of wild-type Spry4 causes a significant reduction in MAPK and Rac1 activation and neurite outgrowth induced by NGF. At molecular level, our findings indicate that ectopic expression of a mutated form of Spry4 (Y53A), in which a conserved tyrosine residue was replaced, fail to block both TrkA-mediated Erk/MAPK activation and neurite outgrowth induced by NGF, suggesting that an intact tyrosine 53 site is required for the inhibitory effect of Spry4 on NGF signaling. Downregulation of Spry4 using small interference RNA knockdown experiments potentiates PC12 cell differentiation and MAPK activation in response to NGF. Together, these findings establish a new physiological mechanism through which Spry4 regulates neurite outgrowth reducing not only the

Mitogen-inducible gene 6 is an endogenous inhibitor of HGF/Met-induced cell migration and neurite growth

In midgestation mouse embryos, the aorta-gonad-mesonephros (AGM) region generates hematopoietic stem cells and definitive hematopoiesis is regulated by cell–cell interaction and signaling molecules. We showed that a Ras/mitogen-activated protein (MAP) kinase signaling-specific inhibitor and a dominant negative mutant Ras blocked the production of CD45 � hematopoietic cells in embryonic day 11.5 AGM culture, indicating an essential role for the MAP kinase pathway in AGM hematopoiesis. Overexpression of the Ras/MAP kinase pathway regulator, Spred-2, in the AGM culture significantly reduced the number of CD45 � cells. In contrast, production of CD45 � cells from the AGM region of Spred-2–null mice was up-regulated as compared with wild-type littermates. Furthermore, Spred-2–deficient mice exhibited elevated hematopoietic colony formation from vascular endothelial-cadherin � cells. These data indicate that Spred-2 functions as a negative regulator of AGM hematopoiesis by inhibiting hematopoietic cytokine signaling. Key words:

regulates junctions and cytoskeleton dynamics during tissue patterning