Fig 6. Testing the shift in regulatory mechanism of mitotic oscillations.
To verify the observation [47] that the number of mitotic divisions in the Drosophila embryo is governed by a shift from negative to positive feedback, we first removed all discrete events and introduced the variable C such that N = 1.95C. We then compared the limit cycles produced by this eventless model (left) with those produced by a variant with attenuated positive feedback from the regulators Wee1 and String (right). Attenuation was achieved by decreasing the rates of the phosphorylation and dephosphorylation of Wee1 and String. The original model exhibits stable limit cycle oscillations for both early cycles (C), which are putatively dominated by negative feedback, and late cycles (E), which are putatively dominated by positive feedback. The attenuated model only exhibits stable oscillations at early cycles (D), suggesting that positive feedback does indeed play a role in late cycle oscillations (F). Our model reuse and modification study is available as a COMBINE archive that reproduces the figure shown and facilitates further modification and reuse [55].