Theoretical DFT interpretation of infrared spectra of biologically active arabinogalactan sulphated derivatives

Arabinogalactan (AG) and sulphated arabinogalactans (SAG) which are products of chemical modification of arabinogalactan polysaccharide with anticoagulant properties were studied by experimental infrared (IR) spectroscopy combined with density functional theory simulations. Mutual analythis of experimental and theoretical IR frequencies indicates that the descripancies between experiment and theory is caused by the influence of -OH groups, which led to the energy shift and broadening of the absorption IR bands. It was found that theoretical and experimental spectra correspond well within 3000-4000 cm-1 spectral region. Addition of sulphur group in AG structure causes hydroxyl group to become accessible for further sulphation. The difference between experimental and theoretical IR frequencies of sulphated AG derivatives is greater than for the parent arabinogalactan due to increase in the number of possible isomers and conformers

The Role of Symmetric Stem Cell Divisions in Tissue Homeostasis

Successful maintenance of cellular lineages critically depends on the fate decision dynamics of stem cells (SCs) upon division. There are three possible strategies with respect to SC fate decision symmetry: (a) asymmetric mode, when each and every SC division produces one SC and one non-SC progeny; (b) symmetric mode, when 50% of all divisions produce two SCs and another 50%-two non-SC progeny; (c) mixed mode, when both the asymmetric and two types of symmetric SC divisions co-exist and are partitioned so that long-term net balance of the lineage output stays constant. Theoretically, either of these strategies can achieve lineage homeostasis. However, it remains unclear which strategy(s) are more advantageous and under what specific circumstances, and what minimal control mechanisms are required to operate them. Here we used stochastic modeling to analyze and quantify the ability of different types of divisions to maintain long-term lineage homeostasis, in the context of different control networks. Using the example of a two-component lineage, consisting of SCs and one type of non-SC progeny, we show that its tight homeostatic control is not necessarily associated with purely asymmetric divisions. Through stochastic analysis and simulations we show that asymmetric divisions can either stabilize or destabilize the lineage system, depending on the underlying control network. We further apply our computational model to biological observations in the context of a two-component lineage of mouse epidermis, where autonomous lineage control has been proposed and notable regional differences, in terms of symmetric division ratio, have been noted-higher in thickened epidermis of the paw skin as compared to ear and tail skin. By using our model we propose a possible explanation for the regional differences in epidermal lineage control strategies. We demonstrate how symmetric divisions can work to stabilize paw epidermis lineage, which experiences high level of micro-injuries and a lack of hair follicles as a back-up source of SCs