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Paris/FFL
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| - | 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). | + | 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). | + | 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. | + | 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.)''. |
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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.)'' | ||
Revision as of 16:51, 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.)
