Modelling, abstraction, and computation in systems biology: A view from computer science

Is Cancer Reversible? Rethinking Carcinogenesis Models-A New Epistemological Tool

A growing number of studies shows that it is possible to induce a phenotypic transformation of cancer cells from malignant to benign. This process is currently known as "tumor reversion". However, the concept of reversibility hardly fits the current cancer models, according to which gene mutations are considered the primary cause of cancer. Indeed, if gene mutations are causative carcinogenic factors, and if gene mutations are irreversible, how long should cancer be considered as an irreversible process? In fact, there is some evidence that intrinsic plasticity of cancerous cells may be therapeutically exploited to promote a phenotypic reprogramming, both in vitro and in vivo. Not only are studies on tumor reversion highlighting a new, exciting research approach, but they are also pushing science to look for new epistemological tools capable of better modeling cancer.

Inference of Model Parameters Using Particle Filter Algorithm and Copula Distributions

It is widely accepted that experimental data often include noise because of the limitation in experimental conditions. In addition, biological systems inside the cells also contain uncertainty due to small copy molecular numbers. To address this issue, it was proposed that experimental data include both real system state and a noise term whose variance is a constant. An additional assumption is that the observation data of different variables are independent to each other. However, recent research works showed that noise in experimental data might not be the white noise. In addition, the observed values of different variables may be correlated. This work designs a new algorithm to infer the unknown model parameters based on noisy data. The innovation of this method includes a new noise model, in which the variance of noise is dependent on the system state, and a copula particle filter algorithm that uses the copula density functions to describe the dependence of different variables. The proposed algorithm is evaluated by using two deterministic models for gene networks and a stochastic model. Numerical results show that the accuracy of our proposed method is better than that of the widely used Liu-West filter and copula particle filter algorithms.

Is the cell really a machine?

It has become customary to conceptualize the living cell as an intricate piece of machinery, different to a man-made machine only in terms of its superior complexity. This familiar understanding grounds the conviction that a cell's organization can be explained reductionistically, as well as the idea that its molecular pathways can be construed as deterministic circuits. The machine conception of the cell owes a great deal of its success to the methods traditionally used in molecular biology. However, the recent introduction of novel experimental techniques capable of tracking individual molecules within cells in real time is leading to the rapid accumulation of data that are inconsistent with an engineering view of the cell. This paper examines four major domains of current research in which the challenges to the machine conception of the cell are particularly pronounced: cellular architecture, protein complexes, intracellular transport, and cellular behaviour. It argues that a new theoretical understanding of the cell is emerging from the study of these phenomena which emphasizes the dynamic, self-organizing nature of its constitution, the fluidity and plasticity of its components, and the stochasticity and non-linearity of its underlying processes.

Theoretical aspects of Systems Biology

The natural world consists of hierarchical levels of complexity that range from subatomic particles and molecules to ecosystems and beyond. This implies that, in order to explain the features and behavior of a whole system, a theory might be required that would operate at the corresponding hierarchical level, i.e. where self-organization processes take place. In the past, biological research has focused on questions that could be answered by a reductionist program of genetics. The organism (and its development) was considered an epiphenomenona of its genes. However, a profound rethinking of the biological paradigm is now underway and it is likely that such a process will lead to a conceptual revolution emerging from the ashes of reductionism. This revolution implies the search for general principles on which a cogent theory of biology might rely. Because much of the logic of living systems is located at higher levels, it is imperative to focus on them. Indeed, both evolution and physiology work on these levels. Thus, by no means Systems Biology could be considered a 'simple' 'gradual' extension of Molecular Biology.

Downward causes and appropriate abstractions: Alternative argument for Noble's position

In his article of this issue, Denis Noble argues that causation can occur at and between any scales - rather than levels - in nature. I agree with this conclusion, but do not find his reasoning fully persuasive. I offer an independent but related argument for his position, which focuses on the role of the process of abstraction in identifying and understanding a phenomenon. My aim is to give the reader another way to think about causal talk within the framework of Systems Biology.