Mechanical characterization of yeast cells: effects of growth conditions.

UNLABELLED: Industrial biotechnology uses microbiological cells to produce a wide range of products. While the organisms in question are well understood regarding their genetic and molecular properties, less is known about their mechanical properties. Previous work has established a testing procedure for single Saccharomyces cerevisiae cells using a Nanoindenter equipped with a Flat Punch probe, allowing the compression between two parallel surfaces. The resulting force-displacement curves clearly showed the bursting of the cells and served to determine characteristic values such as the bursting force, bursting energy and relative deformation. This study examined the mechanical characteristics of yeast cells under the influence of varying cultivation parameters, namely the pH value, temperature, aeration rate, stirrer speed and culture medium composition. It was observed that only temperature and medium composition showed significant effect on the mechanical properties of the cells. Higher temperatures during cultivation caused lower bursting forces and energies. Further analysis of the data showed that the mechanical characteristics of the cells were only influenced by parameters which also had an influence on the growth rate. In conclusion, higher growth rates result in a lower mechanical strength of the yeast cells. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides data on the influence of growth conditions on the mechanical properties of yeast cells. Single cell compression tests on Saccharomyces cerevisiae cells indicate that higher growth rates result in a lower mechanical strength of the cells. As in biotechnological processes mechanical degradation is often part of the downstream process to release the product from the micro-organisms, the knowledge about the mechanical properties of the cells is relevant for process optimization.

Guanine nucleotide exchange factors: activators of Ras superfamily proteins.

Members of the Ras superfamily of proteins function as regulated GDP/GTP switches that cycle between active GTP-complexed and inactive GDP-complexed states. Guanine nucleotide exchange factors (GEFs) stimulate formation of the GTP-bound state, whereas GTPase activating proteins (GAPs) catalyze the formation of the GDP-bound state. We describe three studies that evaluate the mechanism of action of GEFs for Ras (SOS1 and RasGRF/CDC25) or Ras-related Rho (Dbl and Vav) proteins. Growth factor-mediated activation of Ras is believed to be mediated by activation of Ras GEFs (CDC25/GRF and SOS1/2). Although the mechanisms of Ras GEF regulation are unclear, recent studies suggest that translocation of SOS1 to the plasma membrane, where Ras is located, might be responsible for Ras activation. Our observation that the addition of the Ras plasma membrane-targeting sequence to the catalytic domains of CDC25 and SOS1 greatly enhanced their transforming and transactivation activities (10-50 fold and 5-10 fold, respectively) suggests that membrane translocation alone is sufficient to potentiate GEF activation of Ras. We have determined that two Ras-related proteins, designated R-Ras and R-Ras2/TC21, can trigger the malignant transformation of NIH 3T3 cells via activation of the Ras signal transduction pathway. Furthermore, like Ras and R-Ras, we observed that TC21 GTPase activity was stimulated by Ras GAPs. However, we observed that both SOS1 and CDC25 were activators of normal TC21, but not R-Ras, transforming activities. Therefore, TC21, but not R-Ras, may be activated by the same extracellular signaling events that activate Ras proteins. Dbl family proteins are believed to function as GEFs and activators of the Ras-related Rho family of proteins. However, one Dbl family oncogene, designated Vav, has been reported to be a GEF for Ras proteins. Therefore we were interested in determining whether Dbl family oncogenes cause transformation by triggering the constitutive activation of Rho or Ras proteins. Our results suggest that Dbl oncogenes cause transformation via a Ras-independent activation of MAP kinases and Rho family proteins.

Improvement of cardiac performance and metabolism in long-term diabetes mellitus after treatment with insulin [see comment].

Rat hearts induced diabetic by administration of streptozotocin were investigated after 8 months using the isolated perfused working rat heart model at a physiological workload of approximately 45 min. They are hemodynamically characterized by a significantly reduced cardiac output (p < 0.001) and metabolically by a 49% reduction in glucose utilization (p < 0.001), mainly caused by reduced glucose uptake (p < 0.001) and an increased lactate and pyruvate production (p < 0.001), associated with a reduction of oxygen consumption by 44% (p < 0.001). Both lead to reduced ATP and CP myocardial tissue levels (p < 0.001). Similar results with respect to cardiac performance and metabolism are observed already after 2 months of diabetes. Treating these rats after 2 months of diabetes with insulin for 6 months, cardiac output (ns), cardiac metabolism (ns), oxygen uptake (ns) as well as ATP and CP levels (ns) are restored, indicating that normalization of cardiac function in this model depends mainly on the restored cardiac metabolism. These findings were associated with changes in the angioarchitecture as demonstrated.

[The significance of recurrence-inducing events for patients with chronic inflammatory bowel diseases. Results of a prospective longitudinal study over three years]. / Die Bedeutung rezidivauslösender Ereignisse bei Patienten mit chronisch entzündlichen Darmerkrankungen. Ergebnisse einer prospektiven Längsschnittstudie über drei Jahre.

This study examined whether life event stress under general or more specific conditions (fear of separation, feeling of being under pressure, feeling of being caught between two quarreling parties, separation experiences) contribute to the aggravation of inflammatory bowel disease. Firstly, 51 patients with ulcerative colitis, 57 patients with Crohn's disease, and 60 controls were compared in terms of these variables. In addition, the IBD patients filled out questionnaires regarding life events, the specific psychological conditions mentioned above, and their symptoms several times in the three years after the first measurement. By means of group comparisons and intraindividual correlations between relapse precipitating life events and illness activity, only feelings of being under pressure showed a modest correlation to the disease activity. We conclude that the variables in question have little influence on the beginning of the relapse.

[Reciprocity of intrapsychic and interpersonal processes in anorexia nervosa: observations and interpretations from the therapy of the family]. / Zur Wechselwirkung intrapsychischer und interpersoneller Prozesse in der Anorexia nervosa: Beobachtungen und Interpretationen aus der Therapie einer Magersuchtfamilie.

This article uses sections of transcribed tape-recordings of family interviews to elucidate the pubescent anorexia nervosa of a 14 year-old girl within the context of her family interactions. The reciprocal action of intrapsychic disturbance and interpersonal processes within the family, as well as the feedback machanisms involved in both systems are discussed. Analogous to the neurotic aspect of the anorexia itself, the neurotic family dealings with the puberty crisis are shown, which are dedicated to the repression of drive-desires, turn against, a restructuring of family equilibrium necessitated by the life cycles of various family members, resulting in a power struggle for symmetrical positions within the family. Analogous to the internal ego disorder found in anorexia, the permanent struggle to differentiate ego functions and integrate bodily experience and thereby achieve indentity as a separate, autonomous subject is described. The struggle for autonomy is made more difficult by family norms which do not allow for the expression of personal desires, needs and interests. Thoughts on the development of anorexia nervosa relevant to the family situation described in our example follow the phenomenological presentation. The disturbance in self-object differentiation arises from the early mother-child relationship, and is viewed as the result of the mother's disturbed relationship to primary maternal preoccupation. A symbiotic-antagonistic relationship between mother and child is perpetuated by means of mystifying, binding strategies. The family keeps the traditional roles of victim an savior ready to overcome psychosocial crises. Finally, the casuitry explains anorexia as a form of confrontation within a family context, which is moulded by the norms of village social structure.