On the history of the principle of least squares

Communicated by C. Truesdell     

Simulating FAS-induced apoptosis by using P systems

In contrast to differential equations, P systems are an unconventional model of computation which takes into consideration the discrete character of the quantity of components and the inherent randomness that exists in biological phenomena. The key feature of P systems is their compartmentalised structure which represents the heterogeneity of the structural organisation of the cells, and where one can take into account the role played by membranes in the functioning of the system, for example signalling at the cell surface, selective uptake of substances from the media, diffusion across different compartments, etc. We show here that P systems can be a reliable tool for Systems Biology and could even outperform in some cases the current simulation techniques based on differential equations. We will also use a strategy based on the well known Gillespie algorithm but running on more than one compartment called Multi-compartmental Gillespie Algorithm.     

Silencing of unsynapsed meiotic chromosomes in the mouse

In Neurospora, DNA unpaired in meiosis both is silenced and induces silencing of all DNA homologous to it. This process, called meiotic silencing by unpaired DNA, is thought to protect the host genome from invasion by transposable elements. We now show that silencing of unpaired (unsynapsed) chromosome regions also takes place in the mouse during both male and female meiosis. The tumor suppressor protein BRCA1 is implicated in this silencing, mirroring its role in the meiotic silencing of the X and Y chromosomes in normal male meiosis. These findings impact on the interpretation of the relationship between synaptic errors and sterility in mammals and extend our understanding of the biology of Brca1.