Paris/FFL

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If the input function of the promoter of the gene Z is "OR", Z is expressed when X activity is high. There is no delay following the expression of X. But when X is not expressed anymore, its concentration decreases and reach the activation threshold of Y and Z. Y is not expressed anymore but as the concentration decreases, Z is still expressed. '''The OR-gate C1-FFL allow the gene Z to be expressed about one more hour after the gene X is OFF.''' ''(Figure 2.B.)''
If the input function of the promoter of the gene Z is "OR", Z is expressed when X activity is high. There is no delay following the expression of X. But when X is not expressed anymore, its concentration decreases and reach the activation threshold of Y and Z. Y is not expressed anymore but as the concentration decreases, Z is still expressed. '''The OR-gate C1-FFL allow the gene Z to be expressed about one more hour after the gene X is OFF.''' ''(Figure 2.B.)''
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sources : [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16729041|Kalir ''et al''. 2005]
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Bibliography :  
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[http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16729041 Kalir ''et al''. 2005]
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[http://www.ncbi.nlm.nih.gov/pubmed/14607112?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum Mangan ''et al''. 2003]
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[http://www.ncbi.nlm.nih.gov/pubmed/14530388?ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum Mangan ''et al''. 2003]
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[http://www.nature.com/ng/journal/v31/n1/abs/ng881.html Shen-Orr ''et al''. 2002]

Revision as of 17:12, 25 October 2008

A Feed-Forward Loop is a genetic network composed of three nodes. This strong network motif is composed of a transcription factor X that regulates a second transcription factor, Y, and both X and Y regulate Z (Figure 1).

Depending on the type of regulations between the different nodes, we can define eight types of FFL that can be classified into two groups : coherent and incoherent FFLs. In coherent FFLs, the indirect path has the same overall sign as the direct path. The most abundant FFL is the type-1 coherent FFL (C1-FFL) (Figure 1).

In addition to the signs of the edges, to understand the dynamics of the FFL, we must also know how the inputs from the two regulators X and Y are integrated at the promoter of the gene Z. Uri ALON considers that there are two biologically reasonable logic functions : "AND" logic, in which both X and Y activities are need to be high in order to turn on Z expression and "OR" logic in which either X or Y is sufficient (Figure 2.A.).

If the input function of the promoter of the gene Z is "OR", Z is expressed when X activity is high. There is no delay following the expression of X. But when X is not expressed anymore, its concentration decreases and reach the activation threshold of Y and Z. Y is not expressed anymore but as the concentration decreases, Z is still expressed. The OR-gate C1-FFL allow the gene Z to be expressed about one more hour after the gene X is OFF. (Figure 2.B.)

Bibliography : Kalir et al. 2005 Mangan et al. 2003 Mangan et al. 2003 Shen-Orr et al. 2002