Remodelling Chromatin Remodelling.

Not Supplied.

Clockshop Complexity. Computational Approaches to the Rhythms of Life

Endogenous biological rhythms with free-running periods close to 24h are observed in the behaviour and metabolism of allmost any species. These rhythms are usually said to be driven by a "circadian clock", a putative central pacemaker that drives the observable output rhythms. However, since the mid-70s, it has been suggested that the timekeeping of organisms is managed by entire "clockshops" of multiple oscillators, instead of one single pacemaker. In this work I am going to present the results of spatio-temporal data analyses and numerical simulations investigating the multi-oscillator nature of circadian rhythmicity in a plant leaf. Two types of clockshops with different complexities are discussed: i) the multitude of rhythmic cells which compose the leaf tissue. Here, the spatio-temporal dynamics of leaf metabolism, and the formation of synchronization patterns by heterogeneity and external forces are analysed and simulated. ii) the multitude of functionally different oscillators, situated at diverse levels, e.g. gene expression and metabolism. Their existence is predicted from time-series analysis of leaf gas-exchange and comparison with simulations. I will conclude the talk giving a quick outlook to ongoing work on rhythm generation by multi-loop delayed feedback systems and models for the processing of simultaneous environmental rhythms, like, e.g., light and food.

Know thy self. Modeling the basic cognitive properties of the immune system.

The immune system of the vertebrates shows apparent cognitive properties such as the "distinction" between molecular "self" and "not-self", several forms of "learning", and specific "memories". These observations suggest that this multiagent, distributed system is able to make representations of the molecular world. The full understanding of the molecular and cellular mechanism underlying immune behavior may therefore provide useful insights into cognition in general.

To this end, recent advances in modeling the immune system will be reviewed. Mathematical models, quantitative experiments, and real-time imaging of lymphocytes in vitro and in vivo, were used to assess the basic laws governing the dynamics of the cellular components of the immune system, and the interactions amongst them. Simulation of a multiagent model of the immune system controlled by these laws indicates that categories such as "self" and "not-self", are not predefined in the immune system; instead they emerge naturally from the structure and dynamics of the subpopulations of cellular agents, that evolve within the body context. Several methodological and conceptual challenges posed by these insights into the immune system will be pinpointed.

Short and long-term behaviour of childhood diseases on dynamical small-world networks.

We investigate the short and long-term dynamics of childhood diseases with a probabilistic cellular automaton implementation of SIR and SEIR models on a small-world network. Spatial correlations are found to decrease considerably the effective transmission rate and the basic reproductive rate, R0, and to increase the average age at infection. Concurrently they act to enhance the size and coherence of stochastic fluctuations leading to fully developed oscillations.

Persistence was found to depend crucially on the topology of the contact network, this aspect being central to the very definition of the critical community size.

We show that the SEIR implementation allows for quantitative assessment of the pattern of recurrent epidemics in typical childhood diseases by performing long-term simulations using the etiological parameters of measles, pertussis and rubella. Both the period and amplitude of the oscillations are in good agreement with existing data records.