Systematic mapping of cell wall mechanics in the regulation of cell morphogenesis.

Walled cells of plants, fungi, and bacteria come with a large range of shapes and sizes, which are ultimately dictated by the mechanics of their cell wall. This stiff and thin polymeric layer encases the plasma membrane and protects the cells mechanically by opposing large turgor pressure derived mechanical stresses. To date, however, we still lack a quantitative understanding for how local and/or global mechanical properties of the wall support cell morphogenesis. Here, we combine subresolution imaging and laser-mediated wall relaxation to quantitate subcellular values of wall thickness (h) and bulk elastic moduli (Y) in large populations of live mutant cells and in conditions affecting cell diameter in the rod-shaped model fission yeast. We find that lateral wall stiffness, defined by the surface modulus, σ = hY, robustly scales with cell diameter. This scaling is valid across tens of mutants spanning various functions-within the population of individual isogenic strains, along single misshaped cells, and even across the fission yeasts clade. Dynamic modulations of cell diameter by chemical and/or mechanical means suggest that the cell wall can rapidly adapt its surface mechanics, rendering stretched wall portions stiffer than unstretched ones. Size-dependent wall stiffening constrains diameter definition and limits size variations; it may also provide an efficient means to keep elastic strains in the wall below failure strains, potentially promoting cell survival. This quantitative set of data impacts our current understanding of the mechanics of cell walls and its contribution to morphogenesis.

Rituximab as Maintenance Therapy in Type 1 Autoimmune Pancreatitis: An Italian Experience.

OBJECTIVE: Rituximab (RTX) has been proposed for the induction of remission and maintenance therapy in relapsing type 1 autoimmune pancreatitis (AIP). The aim of the study was to describe the use of RTX as maintenance therapy for patients with type 1 AIP. METHODS: Patients with type 1 AIP based on the International Consensus Diagnostic Criteria and treated with RTX were selected from our database. Two doses of RTX (1000 mg each) were administered 15 days apart and repeated after 6 months. RESULTS: Eighteen patients were treated with RTX as maintenance therapy. Of these, the involvement of other organs was observed in 16 patients (89%). Eight of the 18 patients (44%) relapsed during follow-up. Median time to relapse after the last infusion was 30 months (range, 12-35 months). No disease relapse was observed in the first year after the last infusion. Probability of disease relapse was 80% between 1 and 3 years from initial treatment. No adverse effects were observed. CONCLUSIONS: Rituximab seems be safe and effective for maintenance therapy of type 1 AIP during the first year after completing RTX infusion. However, the probability of disease relapse is high within 1 and 3 years from the last infusion.

Mechanosensation Dynamically Coordinates Polar Growth and Cell Wall Assembly to Promote Cell Survival.

How growing cells cope with size expansion while ensuring mechanical integrity is not known. In walled cells, such as those of microbes and plants, growth and viability are both supported by a thin and rigid encasing cell wall (CW). We deciphered the dynamic mechanisms controlling wall surface assembly during cell growth, using a sub-resolution microscopy approach to monitor CW thickness in live rod-shaped fission yeast cells. We found that polar cell growth yielded wall thinning and that thickness negatively influenced growth. Thickness at growing tips exhibited a fluctuating behavior with thickening phases followed by thinning phases, indicative of a delayed feedback promoting thickness homeostasis. This feedback was mediated by mechanosensing through the CW integrity pathway, which probes strain in the wall to adjust synthase localization and activity to surface growth. Mutants defective in thickness homeostasis lysed by rupturing the wall, demonstrating its pivotal role for walled cell survival.

Mechanics and morphogenesis of fission yeast cells.

The integration of biochemical and biomechanical elements is at the heart of morphogenesis. While animal cells are relatively soft objects which shape and mechanics is mostly regulated by cytoskeletal networks, walled cells including those of plants, fungi and bacteria are encased in a rigid cell wall which resist high internal turgor pressure. How these particular mechanical properties may influence basic cellular processes, such as growth, shape and division remains poorly understood. Recent work using the model fungal cell fission yeast, Schizosaccharomyces pombe, highlights important contribution of cell mechanics to various morphogenesis processes. We envision this genetically tractable system to serve as a novel standard for the mechanobiology of walled cell.