Hyperpolarization by glucose of feeding-related neurons in snail

In the pond snail Lymnaea stagnalis, D-glucose action was investigated on electrical activity of identified central neurons. In the CNS preparations isolated from specimens that starved for 24-96 h, D-glucose added to a standard or HiDi saline at 500-700 microg/ml effectively hyperpolarized ca. 90% of feeding related neurons B1, SO and CGC. However, not all feeding-related neurons examined were responsive to glucose. Experiments on cells of the serotonergic Pedal A cluster have shown that hyperpolarizing action of D-glucose is retained following complete isolation of "hunger" neurons. Threshold concentration producing 1-3 mV hyperpolarization was ca. 50 microg/ml. The results suggest a direct glucose involvement in the mechanisms that control feeding behavior in Lymnaea.     

Top-down impact of bacterivorous nematodes on the bacterial community structure: a microcosm study

The influence of bacterivorous nematodes (Diplolaimelloides meyli, Diplolaimelloides oschei, Diplolaimella dievengatensis, Panagrolaimus paetzoldi) on the development of a bacterial community growing on decaying cordgrass detritus was studied in laboratory microcosm experiments. Cordgrass leaves were incubated on a sediment surface with a natural bacterial mixture containing bacteria from sediment, cordgrass detritus and habitat water. The four nematode species were applied separately to the microcosms; controls remained without nematodes. Samples were taken seven times over a 65-day period. The bacterial community structure was analysed by means of DGGE of the 16S rRNA genes. Multi Dimensional Scaling showed grouping of the samples per treatment. Analysis of Similarities indicated that the differences between treatments were significantly larger than differences within treatments. Our results suggest that nematodes can have a significant structuring top-down influence on the 'pool' of bacteria growing on the detritus, even at low densities. Dissimilarities were similar between all treatments. Differences in bacterial community composition within the treatments with monhysterids (D. meyli, D. oschei and D. dievengatensis) can be explained by species-specific food preferences. Panagrolaimus paetzoldi on the other hand feeds unselectively, and thus affects the bacterial community differently. A top-down effect of the nematodes on the diversity of the bacterial community was only evident under high grazing pressure, i.e. in the presence of P. paetzoldi.     

Rabip4' is an effector of rab5 and rab4 and regulates transport through early endosomes

We describe the characterization of an 80-kDa protein cross-reacting with a monoclonal antibody against the human La autoantigen. The 80-kDa protein is a variant of rabip4 with an N-terminal extension of 108 amino acids and is expressed in the same cells. For this reason, we named it rabip4'. rabip4' is a peripheral membrane protein, which colocalized with internalized transferrin and EEA1 on early endosomes. Membrane association required the presence of the FYVE domain and was perturbed by the phosphatidylinositol 3-kinase inhibitor wortmannin. Expression of a dominant negative rabip4' mutant reduced internalization and recycling of transferrin from early endosomes, suggesting that it may be functionally linked to rab4 and rab5. In agreement with this, we found that rabip4' colocalized with the two GTPases on early endosomes and bound specifically and simultaneously to the GTP form of both rab4 and rab5. We conclude that rabip4' may coordinate the activities of rab4 and rab5, regulating membrane dynamics in the early endosomal system.     

Metabolic Changes in <Emphasis Type="Italic">Clostridium absonum</Emphasis> ATCC 27555 Accompanying Induction of Epimerization of a Primary Bile Acid

Some parameters of fermentation have been determined for Clostridium absonum in a chemostat by using a chemically defined medium with glucose as the sole source of carbon and energy. Steady-state continuous cultures were achieved at two dilution rates (D). Trends of the carbon flow were determined by comparison of ratios between the specific rates of formation of the three products of metabolism (lactate, acetate, butyrate). Chenodeoxycholate induced the 7- and 7-hydroxysteroid dehydrogenases of C. absonum. In the presence of this inducer, the growth yield and the carbon recovery decreased, the carbon flow distribution was altered favoring acetate production, and a deficit in the reoxydation of nucleotidic cofactors was observed. In the presence of chenodeoxycholate, C. absonum would favor the production of energy at the expense of the reoxidation of nucleotidic cofactors so as to ensure its growth, and the epimerization of chenodeoxycholate to ursodeoxycholate.     

Down-regulation of Rac activity during beta 2 integrin-mediated adhesion of human neutrophils

In human neutrophils, beta2 integrin engagement mediated a decrease in GTP-bound Rac1 and Rac2. Pretreatment of neutrophils with LY294002 or PP1 (inhibiting phosphatidylinositol 3-kinase (PI 3-kinase) and Src kinases, respectively) partly reversed the beta2 integrin-induced down-regulation of Rac activities. In contrast, beta2 integrins induced stimulation of Cdc42 that was independent of Src family members. The PI 3-kinase dependence of the beta2 integrin-mediated decrease in GTP-bound Rac could be explained by an enhanced Rac-GAP activity, since this activity was blocked by LY204002, whereas PP1 only had a minor effect. The fact that only Rac1 but not Rac2 (the dominating Rac) redistributed to the detergent-insoluble fraction and that it was independent of GTP loading excludes the possibility that down-regulation of Rac activities was due to depletion of GTP-bound Rac from the detergent-soluble fraction. The beta2 integrin-triggered relocalization of Rac1 to the cytoskeleton was enabled by a PI 3-kinase-induced dissociation of Rac1 from LyGDI. The dissociations of Rac1 and Rac2 from LyGDI also explained the PI 3-kinase-dependent translocations of Rac GTPases to the plasma membrane. However, these accumulations of Rac in the membrane, as well as that of p47phox and p67phox, were also regulated by Src tyrosine kinases. Inasmuch as Rac GTPases are part of the NADPH oxidase and the respiratory burst is elicited in neutrophils adherent by beta2 integrins, our results indicate that activation of the NADPH oxidase does not depend on the levels of Rac-GTP but instead requires a beta2 integrin-induced targeting of the Rac GTPases as well as p47phox and p67phox to the plasma membrane.     

Evidence for a role of Sky1p-mediated phosphorylation in 3' splice site recognition involving both Prp8 and Prp17/Slu4

The SRPK family of kinases is specific for RS domain-containing splicing factors and known to play a critical role in protein-protein interaction and intracellular distribution of their substrates in both yeast and mammalian cells. However, the function of these kinases in pre-mRNA splicing remains unclear. Here we report that SKY1, a SRPK family member in Saccharomyces cerevisiae, genetically interacts with PRP8 and PRP17/SLU4, both of which are involved in splice site selection during pre-mRNA splicing. Prp8 is essential for splicing and is known to interact with both 5' and 3' splice sites in the spliceosomal catalytic center, whereas Prp17/Slu4 is nonessential and is required only for efficient recognition of the 3' splice site. Interestingly, deletion of SKY1 was synthetically lethal with all prp17 mutants tested, but only with specific prp8 alleles in a domain implicated in governing fidelity of 3'AG recognition. Indeed, deletion of SKY1 specifically suppressed 3'AG mutations in ACT1-CUP1 splicing reporters. These results suggest for the first time that 3' AG recognition may be subject to phosphorylation regulation by Sky1p during pre-mRNA splicing.     

The Interaction of Gibberellins and Photoperiod in the Control of Potato Tuberization

Solanum tuberosum ssp. andigena plants require a short-day (SD) photoperiod for tuber formation, a process that is also affected by gibberellins (GAs). Grafting experiments have confirmed that the photoperiod is perceived in the leaves. Tuber formation, however, usually takes place in the underground stolons. In this review, photoperiod-dependent tuberization has been divided into five chronological events: SD photoperiod perception, short-term adaptive responses to SD conditions, generation and transport of tuber-inducing signal(s), tuber formation, and long-term adaptive responses to tuber growth. Within this frame of study, the interaction of GAs and photoperiod is revised. Similar to the flowering process in Arabidopsis, we suggest the existence of two independent pathways that control tuber formation: a photoperiod-dependent pathway and a GA-dependent pathway. Nevertheless, photoperiod-dependent tuber formation requires the action of GAs at specific stages to orchestrate this complex process of development.     

Functional studies of the kidney of living animals using multicolor two-photon microscopy

Optical microscopy, when applied to livinganimals, provides a powerful means of studying cell biology in the mostphysiologically relevant setting. The ability of two-photon microscopyto collect optical sections deep into biological tissues has opened upthe field of intravital microscopy to high-resolution studies of the brain, lens, skin, and tumors. Here we present examples of the way inwhich two-photon microscopy can be applied to intravital studies ofkidney physiology. Because the kidney is easily externalized withoutcompromising its function, microscopy can be used to evaluate variousaspects of renal function in vivo. These include cell vitality andapoptosis, fluid transport, receptor-mediated endocytosis, blood flow, and leukocyte trafficking. Efficient two-photon excitation of multiple fluorophores permits comparison of multiple probes andsimultaneous characterization of multiple parameters and yields spectral information that is crucial to the interpretation of imagescontaining uncharacterized autofluorescence. The studies described heredemonstrate the way in which two-photon microscopy can provide a levelof resolution previously unattainable in intravital microscopy,enabling kinetic analyses and physiological studies of the organs ofliving animals with subcellular resolution.