Estimation of turgor pressure through comparison between single plant cell and pressurized shell mechanics.

While plant growth is well known to rely on turgor pressure, it is challenging to quantify the contribution of turgor pressure to plant cell rheology. Here we used a custom-made micro-rheometer to quantify the viscoelastic behavior of isolated plant cells while varying their internal turgor pressure. To get insight into how plant cells adapt their internal pressure to the osmolarity of their medium, we compared the mechanical behavior of single plant cells to that of a simple, passive, pressurized shell: a soccer ball. While both systems exhibited the same qualitative behavior, a simple mechanical model allowed us to quantify turgor pressure regulation at the single cell scale.

Emergence and development of gut motility in the chicken embryo.

The gastrointestinal tract transports the food bolus by peristalsis. Gut motility starts at an early age in the developing embryo, well before it is required for nutrition of the organism. We present a comprehensive kinematic study of the emergence and physiological development of gut motility in all regions of the lower digestive tract of the chicken embryo from embryonic days E5 through E9. We characterized motility emergence time, propagation patterns, speed, frequency and amplitude of peristalsis waves. We found that the emergence of an uninterrupted circular ring of smooth muscle correlated with the appearance of propagative contractile waves, at E6 in the hindgut and midgut, and at E9 in the caecal appendix. We show that peristalsis at these stages is critically dependent on calcium and is not mediated by neurons as gut motility is insensitive to tetrodotoxin and takes place in the hindgut in the absence of neurons. We further demonstrate that motility also matures in ex-vivo organ culture. We compare our results to existing literature on zebrafish, mouse and human motility development, and discuss their chronological relationship with other major developmental events occurring in the chicken embryonic gut at these stages. Our work sets a baseline for further investigations of motility development in this important animal model.

Analyzing the interplay between single cell rheology and force generation through large deformation finite element models.

In this study, experimental results of single cell spreading between two parallel microplates are exploited through finite element modeling. Axisymmetric computations at finite strains are performed to extract the mechanical properties of the cell which can account for cell shape evolution and traction force generation. Our model includes two distinct components representing the cortex associated with the bilayer membrane on the one hand, and the rest of the cell on the other hand. The former is modeled as a homogeneous hyperelastic material described by a slightly compressible Gent strain energy function, while the latter is idealized either as a quasi-incompressible Newtonian fluid or as another homogeneous hyperelastic material. The kinetics of spreading is ensured by a stapling procedure defined from experimental observations. Material parameters are then optimized to match the simulation closely with the experimental data. In particular, the elastic modulus of the cortex is estimated at about 1,000 Pa in both models, while the cell interior is characterized by a viscosity of 1,000 Pa.s in the biphasic model, or by an elastic modulus of about 100 Pa in the hyperelastic one. These results are in good agreement with G(') and G('') measurements carried out previously in the same parallel plates setup and estimated at the typical rate of cell straining. Moreover, stresses are found to concentrate at the edge of the cell-substrate contact area. These observations allow explaining the relationship between cell spreading and force increase since spreading and the consequent straining of the cell mechanical structure could be the source of the force applied by the cell on its substrate. They could also explain, in a very simple manner, why force-sensitive focal contacts concentrate at the cell edges.

FOLFIRI.3, a new regimen combining 5-fluorouracil, folinic acid and irinotecan, for advanced pancreatic cancer: results of an Association des Gastro-Enterologues Oncologues (Gastroenterologist Oncologist Association) multicenter phase II study.

BACKGROUND: The purpose of the study was to prospectively evaluate the efficacy and tolerability of the FOLFIRI.3 regimen in patients with unresectable pancreatic adenocarcinoma. PATIENTS AND METHODS: Chemotherapy-naive patients with histologically proven advanced pancreatic adenocarcinoma were treated with the FOLFIRI.3 regimen, consisting of irinotecan 90 mg/m(2) as a 60-min infusion on day 1, leucovorin 400 mg/m(2) as a 2-h infusion on day 1, followed by 5-fluorouracil (5-FU) 2000 mg/m(2) as a 46-h infusion and irinotecan 90 mg/m(2), repeated on day 3, at the end of the 5-FU infusion, every 2 weeks. RESULTS: Forty patients were enrolled, of whom 29 (73%) had metastatic disease. A total of 441 cycles were delivered (1-53). Grade 3-4 neutropenia occurred in 35% of the patients, accompanied by fever in two cases. Other relevant grade 3-4 toxic effects were nausea-vomiting (27%) and diarrhea (25%). Grade 2 alopecia occurred in 48% of the patients. There were no treatment-related deaths. The confirmed response rate was 37.5%. Stable disease was observed in 27.5% of the patients. The median progression-free and overall survivals were 5.6 months and 12.1 months, respectively. The 1-year survival rate was 51%. CONCLUSION: The FOLFIRI.3 regimen seems to be active on advanced pancreatic cancer and to have a manageable toxicity profile. The lack of cross-resistance between FOLFIRI.3 and gemcitabine-based regimens allows efficient second-line therapies.