Lysosomotropic detergents induce time- and dose-dependent apoptosis/necrosis in cultured cells

Abstract

Oxidative stress has been found to cause lysosomal rupture due to iron-catalyzed intralysosomal oxidative reactions.^1,2 Moderate rupture induces apoptosis, while necrosis follows a more complete relocation of this type.² We have suggested that lysosomal cysteine proteases may directly activate the caspase cascade and, together with other lysosomal hydrolases, induce mitochondrial release of cytochrome c with ensuing further activation of the cascade.     

Tightly regulated, beta-estradiol dose-dependent expression system for yeast

We have refined the regulated expression of UASGAL1, 10-driven genes in yeast by modifying a vector encoding the beta-estradiol inducible activator, GAL4.ER.VP16 (GEV). The expression of GEV was placed under the regulation of the low-level, constitutive MRP7 promoter, and beta-estradiol-regulated expression was monitored by the expression of an integrated UASGAL10-lacZ reporter and by immunoblot analysis of a UASGAL1-regulated gene product. Target gene expression regulated by low levels of GEV has several advantages over the standard galactose-inducible expression systems. (i) Most importantly, the target gene expression is undetectable in the absence of hormone; (ii) target gene expression is beta-estradiol dose-dependent, and variable levels of target gene expression from low to several hundred-fold induction can be achieved; and (iii) induction or depletion studies can be conducted independent of carbon source in gal4 delta strains. In addition, any UASGAL1,10 expression construct can be used without modification of the target gene or many gal4 delta host strains, and GEV vectors are compatible with other inducible yeast expression systems. This method may be useful to researchers investigating the functions of essential genes, dominant negative mutants, mitochondrial genes, and viral, plant, and mammalian genes in yeast assay systems.     

Learning the same motor task twice impairs its retention in a time- and dose-dependent manner

Anterograde interference emerges when two differing tasks are learned in close temporal proximity, an effect repeatedly attributed to a competition between differing task memories. However, recent development alternatively suggests that initial learning may trigger a refractory period that occludes neuroplasticity and impairs subsequent learning, consequently mediating interference independently of memory competition. Accordingly, this study tested the hypothesis that interference can emerge when the same motor task is being learned twice, that is when competition between memories is prevented. In a first experiment, the inter-session interval (ISI) between two identical motor learning sessions was manipulated to be 2 min, 1 h or 24 h. Results revealed that retention of the second session was impaired as compared to the first one when the ISI was 2 min but not when it was 1 h or 24 h, indicating a time-dependent process. Results from a second experiment replicated those of the first one and revealed that adding a third motor learning session with a 2 min ISI further impaired retention, indicating a dose-dependent process. Results from a third experiment revealed that the retention impairments did not take place when a learning session was preceded by simple rehearsal of the motor task without concurrent learning, thus ruling out fatigue and confirming that retention is impaired specifically when preceded by a learning session. Altogether, the present results suggest that competing memories is not the sole mechanism mediating anterograde interference and introduce the possibility that a time- and dose-dependent refractory period—independent of fatigue—also contributes to its emergence. One possibility is that learning transiently perturbs the homeostasis of learning-related neuronal substrates. Introducing additional learning when homeostasis is still perturbed may not only impair performance improvements, but also memory formation.