Figure 3

The formation of the single-stripe pattern by 3-gene networks based on the four Incoherent Feed-Forward Motifs.

The upper part of the figure shows the stripe-forming IFFMs reinforced with positive feedbacks, having from 4 to 6 interactions. Only interactions that generate positive feedbacks have been included. Within the I₁ and I₃ branches of stripe-forming networks, thick solid-line arrows imply adding C self-activation, the dashed-line arrows, B self-activation and the dotted-line arrows, mutual-interaction (i.e. mutual-inhibition or mutual-activation). The lower rectangle in the figure includes the four IFFMs and the underlying process of stripe formation. It shows the generic stripes of the I₁ and I₃ networks, the lack of stripe for I₄ and the barely-detectable one for I₂. Within the rectangle, the upper graphs single out the individual contributions into the stripe-gene promoter for an increasing morphogen, M: from gene A in red and from gene C in blue. For simplicity, we chose to use the concentration of A for the horizontal axis, instead the morphogen concentration. The lower graphs show the resultant expression from gene B. The Gray areas represent non-biological negative values for the concentration A and conceptually illustrate that I₄ would require a negative concentration of A to show a stripe. The range of (non-biological) negative concentration for protein A is also included for illustrative purposes.