Intrinsic Migratory Properties of Cultured Schwann Cells Based on Single-Cell Migration Assay

The migration of Schwann cells is critical for development of peripheral nervous system and is essential for regeneration and remyelination after nerve injury. Although several factors have been identified to regulate Schwann cell migration, intrinsic migratory properties of Schwann cells remain elusive. In this study, based on time-lapse imaging of single isolated Schwann cells, we examined the intrinsic migratory properties of Schwann cells and the molecular cytoskeletal machinery of soma translocation during migration. We found that cultured Schwann cells displayed three motile phenotypes, which could transform into each other spontaneously during their migration. Local disruption of F-actin polymerization at leading front by a Cytochalasin D or Latrunculin A gradient induced collapse of leading front, and then inhibited soma translocation. Moreover, in migrating Schwann cells, myosin II activity displayed a polarized distribution, with the leading process exhibiting higher expression than the soma and trailing process. Decreasing this front-to-rear difference of myosin II activity by frontal application of a ML-7 or BDM (myosin II inhibitors) gradient induced the collapse of leading front and reversed soma translocation, whereas, increasing this front-to-rear difference of myosin II activity by rear application of a ML-7 or BDM gradient or frontal application of a Caly (myosin II activator) gradient accelerated soma translocation. Taken together, these results suggest that during migration, Schwann cells display malleable motile phenotypes and the extension of leading front dependent on F-actin polymerization pulls soma forward translocation mediated by myosin II activity.     

Sex-specific aggression and sex ratio in wintering finch flocks: serins and siskins differ

Males are dominant over females in many bird species. This may lead to male monopolisation of resources whenever food is scarce or clumped and secondarily to lower female survival rates. As a result of the consequent male-biased sex ratio in the adult population, competition may arise either (1) between males and females, as males attempt to exclude females from feeding patches, or (2) between males because females do not pose a competitive threat. We recorded agonistic interactions between males and females in wintering foraging flocks of serins (Serinus serinus) and siskins (Carduelis spinus) to test for inter-specific differences. Most of the aggressive interactions in serins were between males and females, whereas in siskins they were between males. We also compared sex ratios for each species during the winter, determined from separate trapping efforts over an 11-year period, to test whether the direction of aggression by males (i.e. male/male; male/female) relates to variations in female survival rates. The proportion of females was smaller in winter than in autumn for serins, but differences in siskins were negligible. Results are interpreted in relation to the social organization displayed by both species studied.     

Microplate coagulation assays.

This report describes the development of microplate-based blood coagulation assays. The assays require a kinetic microplate reader to follow changes in absorbance at 405 nm caused by the coagulating plasma. Procedures for performing prothrombin time and activated partial thromboplastin time tests are described with intra- and inter-assay variability of a few percentage points. The prothrombin time of normal plasma was 64.5 +/- 3.6 s, and the activated partial thromboplastin time was 69.8 +/- 3.2 s. Clotting times were prolonged when normal plasma was mixed with plasmas deficient in particular coagulation factors, as expected. These assays take advantage of the microplate format (small sample size and multiple simultaneous assays) and can be customized for specific purposes, such as quantifying purified factor IX or assessing protein C activity in plasma.     

Evaluation of mammalian fed-batch cultivations by two different models

Simulations of fed-batch hybridoma cell cultures were performed with two different models, a new model suggested by Nielsen and an older model suggested by Batt and Kompala. The response of the new Nielsen model was less sensitive to changes in feed concentrations and frequencies than the Batt and Kompala model. The new simulations with the Nielsen model as well as those previously with the Batt and Kompala model indicate, that possible benefits of fed-batch cultivations must be sought in other features than in intrinsic metabolic kinetics.