Fig. 6

Three different types of sequential segmentation can evolve (persistent signal, no CCS). a In these simulations, the morphogen is highly expressed in the posterior-most cell. If that cell divides, morphogen expression is maintained in the posterior daughter, and its level decays in the other cells. b–d Space–time plots, networks and division gene dynamics of different types of sequential segmentation. In the networks, the morphogen is circled in yellow, the division gene in magenta and the segmentation gene in blue. In the graphs, the division gene dynamics are depicted only for the posterior-most cell, with high morphogen level. The red line shows the network dynamics if halving of the division protein due to divisions is taken into account. The blue line depicts the dynamics if the network is run without halving the division protein once it reaches the division threshold. b A smoothly growing individual. Note how the division gene is only regulated by the morphogen. c “Wavy” posterior growth. The growth zone keeps dividing, but sometimes its daughters also divide. Note the oscillating expression of the division gene in the posterior-most cell. d “Stair-like” posterior growth. The division gene strongly oscillates and is therefore regularly low even in the posterior cell