Neuron-glia cross talk revealed in reverberating networks by simultaneous extracellular recording of spikes and astrocytes' glutamate transporter and K+ currents.

Astrocytes uptake synaptically released glutamate with electrogenic transporters (GluT) and buffer the spike-dependent extracellular K+ excess with background K+ channels. We studied neuronal spikes and the slower astrocytic signals on reverberating neocortical cultures and organotypic slices from mouse brains. Spike trains and glial responses were simultaneously captured from individual sites of multielectrode arrays (MEA) by splitting the recorded traces into appropriate filters and reconstructing the original signal by deconvolution. GluT currents were identified by using dl-threo-ß-benzyloxyaspartate (TBOA). K+ currents were blocked by 30 µM Ba2+, suggesting a major contribution of inwardly rectifying K+ currents. Both types of current were tightly correlated with the spike rate, and their astrocytic origin was tested in primary cultures by blocking glial proliferation with cytosine ß-d-arabinofuranoside (AraC). The spike-related, time-locked inward and outward K+ currents in different regions of the astrocyte syncytium were consistent with the assumptions of the spatial K+ buffering model. In organotypic slices from ventral tegmental area and prefrontal cortex, the GluT current amplitudes exceeded those observed in primary cultures by several orders of magnitude, which allowed to directly measure transporter currents with a single electrode. Simultaneously measuring cell signals displaying widely different amplitudes and kinetics will help clarify the neuron-glia interplay and make it possible to follow the cross talk between different cell types in excitable as well as nonexcitable tissue.

[Beta-fructofuranosidase--properties, structure and applications]. / Beta-fruktofuranozydaza--wlasciwosci, struktura i zastosowanie.

Beta-fructofuranosidase is the enzyme which releases terminal non-reducing beta-D-fructofuranoside residues in beta-D-fructofuranosides--saccharides commonly found in plants. Under appropriate conditions this enzyme may also catalyze the reaction of synthesis. Now, beta-fructofuranosidase is one of best biochemically characterized enzymes. Also the 3D structure of this protein has been determined. Resolution of the conformation of beta fructofuranosidase--so far only from a few microorganisms--has allowed for the partial explanation of its substrate specificity and understanding of mechanisms of enzymatic catalysis. This article presents a review of current reports on properties of beta-fructofuranosidases derived from various sources with focus on their structure, mechanism of action, biosynthesis and industrial applications.

Intermediate progenitors in adult hippocampal neurogenesis: Tbr2 expression and coordinate regulation of neuronal output.

Neurogenesis in the adult hippocampus is a highly regulated process that originates from multipotent progenitors in the subgranular zone (SGZ). Currently, little is known about molecular mechanisms that regulate proliferation and differentiation in the SGZ. To study the role of transcription factors (TFs), we focused on Tbr2 (T-box brain gene 2), which has been implicated previously in developmental glutamatergic neurogenesis. In adult mouse hippocampus, Tbr2 protein and Tbr2-GFP (green fluorescent protein) transgene expression were specifically localized to intermediate-stage progenitor cells (IPCs), a type of transit amplifying cells. The Tbr2+ IPCs were highly responsive to neurogenic stimuli, more than doubling after voluntary wheel running. Notably, the Tbr2+ IPCs formed cellular clusters, the average size of which (Tbr2+ cells per cluster) likewise more than doubled in runners. Conversely, Tbr2+ IPCs were selectively depleted by antimitotic drugs, known to suppress neurogenesis. After cessation of antimitotic treatment, recovery of neurogenesis was paralleled by recovery of Tbr2+ IPCs, including a transient rebound above baseline numbers. Finally, Tbr2 was examined in the context of additional TFs that, together, define a TF cascade in embryonic neocortical neurogenesis (Pax6 --> Ngn2 --> Tbr2 --> NeuroD --> Tbr1). Remarkably, the same TF cascade was found to be linked to stages of neuronal lineage progression in adult SGZ. These results suggest that Tbr2+ IPCs play a major role in the regulation of adult hippocampal neurogenesis, and that a similar transcriptional program controls neurogenesis in adult SGZ as in embryonic cerebral cortex.

Enhanced invertase activities in the galls of Hormaphis hamamelidis.

Invertases are sucrose hydrolyzing enzymes often associated with plant tissues acting as physiological sinks, and plant galls are physiological sinks. We investigated several types of invertase and their potential benefits in galls of the aphid Hormaphis hamamelidis. Invertase activities in galls differed from those in leaves throughout the growing season. Vacuolar invertase activities (per g FW) were always greater in galls than leaves. In contrast, cell wall invertase activities per g FW started low in galls, but increased with time and were greater than those in leaves after 1 month. Gall growth was most closely related to vacuolar invertase activity, whereas leaf growth was correlated with both vacuolar and cell wall invertase activities. In separate correlational studies of aphid fecundity and invertase activities, cell wall invertase activity per gall accounted for 15-21% of the variation in offspring per gall. Gall dry weight explained more of the variation in offspring per gall (34.2%) than did gall volume (17.8%), a likely indication of the importance of sink strength over the life of the gall. Increased invertase activity probably underlies the enhanced sink strength commonly observed in galls. Hormaphis hamamelidis fundatrices appear to maximize reproductive output by eliciting multiple beneficial responses from their hosts. Initial gall growth correlated positively with high vacuolar invertase activity, while later in the season aphid fecundity correlated positively with cell wall invertase activity.