Boolean (BL) systems and coupled ordinary differential equations (ODEs) are
popular models for studying biological networks. BL systems can be set up without
detailed reaction mechanisms and rate constants and provide qualitatively useful
information, but they cannot capture the continuous dynamics of biological
systems. On the other hand, ODEs are able to capture the continuous dynamic
features of biological networks and provide more information on how the
activities of components depend on other components and parameter values.
However, a useful coupled ODE model requires details about interactions and
parameter values. The introduction of the relationships between the two types of
models will enable us to leverage their advantages and better understand the
target network systems. In this paper, we investigate the relations between
the conditions of the existence of limit cycles in ODE networks and their
homologous discrete systems. We prove that for a single feedback loop, as long as
the corresponding governing functions of the homologous continuous and
discrete systems have the same upper and lower asymptotes, the limit cycle
borne via Hopf bifurcation corresponds to the cycle of the discrete system.
However, for some coupled feedback loops, besides having the same upper
and lower asymptotes, parameters such as the decay rates also play crucial
roles.
This paper is dedicated to our dear
friend Professor Kiran Chilakamarri who passed away due to a
sudden illness in 2015.