Gene regulation is one of the most interesting open problems in modern molecular biology. In this talk I will discuss in particular a class of regulatory motifs known as "mixed feed forward loops (mFFLs)". These motifs seem to be under positive selection in the human regulatory network, thus suggesting that they should play some important functional role. Moreover, in human, several of the genes involved in these mFFLs are known to be oncogenes (i.e. genes related to cancer progression). Our proposal is that these mFFLs are used by the cell to keep under control the stochastic fluctuations in the amount of proteins expressed by the target genes and that for this reason their disregulation plays such an important role in cancer progression. The talk will be divided in two parts. The first will be devoted to a short pedagogical introduction to the organization of Eukaryotic genomes and to the mechanisms of gene regulation. Then in the second part I will discuss, using both stochastic equations and bioinformatic tools the role played by mFFLs in the regulatory network.
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