The mitochondrial Na+/Ca2+ exchanger plays a key role in the control of cytosolic Ca2+ oscillations

There is increasing evidence that mitochondria play an important role in the control of cytosolic Ca2+ signaling. We show here that the main mitochondrial Ca2+-exit pathway, the mitochondrial Na+/Ca2+ exchanger, controls the pattern of cytosolic Ca2+ oscillations in non-excitable cells. In HeLa cells, the inhibitor of the mitochondrial Na+/Ca2+ exchanger CGP37157 changed the pattern of the oscillations induced by histamine from a high-frequency irregular one to a lower frequency baseline spike type, surprisingly with little changes in the average Ca2+ values of a large cell population. In human fibroblasts, CGP37157 increased the frequency of the baseline oscillations in cells having spontaneous activity and induced the generation of oscillations in cells without spontaneous activity. This effect was dose-dependent, disappeared when the inhibitor was washed out and was not mimicked by mitochondrial depolarization. CGP37157 increased mitochondrial [Ca2+] and ATP production in histamine-stimulated HeLa cells, but the effect on ATP production was only transient. CGP37157 also activated histamine-induced Ca2+ release from the endoplasmic reticulum and increased the size of the cytosolic Ca2+ peak induced by histamine in HeLa cells. Our results suggest that the mitochondrial Na+/Ca2+ exchanger directly modulates inositol 1,4,5-trisphosphate-induced Ca2+ release and in that way controls cytosolic Ca2+ oscillations.     

Event-driven time-optimal control for a class of discontinuous bioreactors

Discontinuous bioreactors may be further optimized for processing inhibitory substrates using a convenient fed-batch mode. To do so the filling rate must be controlled in such a way as to push the reaction rate to its maximum value, by increasing the substrate concentration just up to the point where inhibition begins. However, an exact optimal controller requires measuring several variables (e.g., substrate concentrations in the feed and in the tank) and also good model knowledge (e.g., yield and kinetic parameters), requirements rarely satisfied in real applications. An environmentally important case, that exemplifies all these handicaps, is toxicant wastewater treatment. There the lack of online practical pollutant sensors may allow unforeseen high shock loads to be fed to the bioreactor, causing biomass inhibition that slows down the treatment process and, in extreme cases, even renders the biological process useless. In this work an event-driven time-optimal control (ED-TOC) is proposed to circumvent these limitations. We show how to detect a "there is inhibition" event by using some computable function of the available measurements. This event drives the ED-TOC to stop the filling. Later, by detecting the symmetric event, "there is no inhibition," the ED-TOC may restart the filling. A fill-react cycling then maintains the process safely hovering near its maximum reaction rate, allowing a robust and practically time-optimal operation of the bioreactor. An experimental study case of a wastewater treatment process application is presented. There the dissolved oxygen concentration was used to detect the events needed to drive the controller.     

Impact of long-term partial aeration on the removal of 2,4,6-trichlorophenol in an initially methanogenic fluidized bed bioreactor

A fluidized bed bioreactor (FBBR) was operated for more than 1000 days under two regimes, Methanogenic (M) and Methanogenic-Aerobic (M-A), to remove 2,4,6-trichlorophenol (TCP) and phenol (Phe) from a synthetic wastewater, containing different amounts of TCP and Phe, using different aeration flow-rates (0, 2.13, and 1.06 NL O(2)/L.day). M conditions (80:20 mg/L of TCP:Phe, 0 NL O(2)/L.day) showed similar TCP and Phe removal (>95%). Nevertheless accumulation of 4-chlorophenol (4CP) up to 16 mg/L and Phe up to 4 mg/L was observed, while in M-A conditions (80:20 mg/L of TCP:Phe, 2.13 NL O(2)/L.day) TCP and Phe removal achieved 99.9(+)% and after 70 days no accumulation of intermediates were detected. The increase of TCP and Phe in the influent under M-A conditions from 80:20 to 120:30 mg/L of TCP:Phe did not negatively affect the removal of TCP, intermediates and Phe; in fact, they were similar to those in previous M-A conditions. The decrease in the oxygen flow rate from 2.13 to 1.06 NL O(2)/L.day had no negative effect on pollutant removals, which were as high as in previous two M-A conditions. The specific methanogenic activity of bioparticles of the fluidized bed decreased with long-term partial aeration, starting from 1.097 mmol CH(4)/h.g(TKN) in the M regime (day 60) to <0.02 mmolCH(4)/h.g(TKN) at day 1050, suggesting aerobic regime in the bioreactor rather than an M-A regime. In conclusion, complete removal of TCP and less chlorinated intermediates could be achieved in an initially methanogenic FBBR under conditions of partial aeration, although long-term operation seemed to negatively affect the methanogenic activity of biomass. It is also likely that after extended aeration the microbial community was finally enriched with strains with the ability to attack 2,4,6-TCP under aerobic conditions. This report represents the first evidence of a long exposure to oxygen of an anaerobic microbial consortium that efficiently remove TCP.     

Assembly of spermatid acrosome depends on microtubule organization during mammalian spermiogenesis

The acrosome is a secretory vesicle attached to the nucleus of the sperm. Our hypothesis is that microtubules participate in the membrane traffic between the Golgi apparatus and acrosome during the first steps of spermatid differentiation. In this work, we show that nocodazole-induced microtubule depolarization triggers the formation of vesicles of the acrosomal membrane, without detaching the acrosome from the nuclear envelope. Nocodazole also induced fragmentation of the Golgi apparatus as determined by antibodies against giantin, golgin-97 and GM130, and electron microscopy. Conversely, neither the acrosome nor the Golgi apparatus underwent fragmentation in elongating spermatids (acrosome- and maturation-phase). The microtubule network of round spermatids of azh/azh mice also became disorganized. Disorganization correlated with fragmentation of the acrosome and the Golgi apparatus, as evaluated by domain-specific markers. Elongating spermatids (acrosome and maturation-phase) of azh/azh mice also had alterations in microtubule organization, acrosome, and Golgi apparatus. Finally, the spermatozoa of azh/azh mice displayed aberrant localization of the acrosomal protein sp56 in both the post-acrosomal and flagellum domains. Our results suggest that microtubules participate in the formation and/or maintenance of the structure of the acrosome and the Golgi apparatus and that the organization of the microtubules in round spermatids is key to sorting acrosomal proteins to the proper organelle.     

Local origin and diversification among Lampornis hummingbirds: a Mesoamerican taxon

The huge biodiversity found in Mesoamerica is often explained by its geographic situation as a natural bridge between two large biogeographic regions. Often overlooked, however, are the high levels of speciation and diversification in the area. Here we assess the phylogenetic relationships within a Mesoamerican group of hummingbirds (Lampornis). We sequenced both mtDNA (1,143 bp of cyt b and 727 bp of ND5) and nuclear genes (505 bp of AK-5 intron and 567 bp of c-mos) for each of the seven recognised species and outgroups. We find two or three clades of similar age within this genus: L. clemenciae and L. amethystinus (singly or as each other's sister taxa) and a Central American clade. This Central-American clade presents a clear bipartition between northern (L. viridipallens and L. sybillae) and southern Mesoamerica, which is shared with many other Mesoamerican organisms. Our analyses suggest that L. hemileucus does not belong in the genus Lampornis. While we refrain to apply a time-scale to our data because of the lack of an appropriate calibration, our results indicate that the genus Lampornis predates the uprising of the Panama land-bridge, and that diversification among the isthmian species (L. castaneoventris and L. calolaema) is a very recent event. Our results strongly suggest a local Mesoamerican origin for this genus.     

CD38 and CD157 as receptors of the immune system: a bridge between innate and adaptive immunity

This paper reviews some of the results and the speculations presented at the Torino CD38 Meeting in June, 2006 and focused on CD38 and CD157 seen as a family of molecules acting as surface receptors of immune cells. This partisan view was adopted in the attempt to combine the enzymatic functions with what the immunologists consider key functions in different cell models. At the moment, it is unclear whether the two functions are correlated, indifferent, or independent. Here we present conclusions inferred exclusively on human cell models, namely T and B lymphocytes, dendritic cells, and granulocytes. As an extra analytical tool, we try to follow in the history of life when the enzymatic and receptorial functions were generated, mixing ontogeny, membrane localization, and cell anchorage.     

A critical review on the improvement of photosynthetic carbon assimilation in C3 plants using genetic engineering

Global warming is one of the most serious challenges facing us today. It may be linked to the increase in atmospheric CO2 and other greenhouse gases (GHGs), leading to a rise in sea level, notable shifts in ecosystems, and in the frequency and intensity of wild fires. There is a strong interest in stabilizing the atmospheric concentration of CO2 and other GHGs by decreasing carbon emission and/or increasing carbon sequestration. Biotic sequestration is an important and effective strategy to mitigate the effects of rising atmospheric CO2 concentrations by increasing carbon sequestration and storage capacity of ecosystems using plant photosynthesis and by decreasing carbon emission using biofuel rather than fossil fuel. Improvement of photosynthetic carbon assimilation, using transgenic engineering, potentially provides a set of available and effective tools for enhancing plant carbon sequestration. In this review, firstly different biological methods of CO2 assimilation in C3, C4 and CAM plants are introduced and three types of C4 pathways which have high photosynthetic performance and have evolved as CO2 pumps are briefly summarized. Then (i) the improvement of photosynthetic carbon assimilation of C3 plants by transgenic engineering using non-C4 genes, and (ii) the overexpression of individual or multiple C4 cycle photosynthetic genes (PEPC, PPDK, PCK, NADP-ME and NADP-MDH) in transgenic C3 plants (e.g. tobacco, potato, rice and Arabidopsis) are highlighted. Some transgenic C3 plants (e.g. tobacco, rice and Arabidopsis) overexpressing the FBP/SBPase, ictB and cytochrome c6 genes showed positive effects on photosynthetic efficiency and growth characteristics. However, over the last 28 years, efforts to overexpress individual, double or multiple C4 enzymes in C3 plants like tobacco, potato, rice, and Arabidopsis have produced mixed results that do not confirm or eliminate the possibility of improving photosynthesis of C3 plants by this approach. Finally, a prospect is provided on the challenges of enhancing carbon assimilation of C3 plants using transgenic engineering in the face of global warming, and the trends of the most promising approaches to improving the photosynthetic performance of C3 plants.     

Preliminary methylation analysis of prothymosin α genomic sequences

Prothymosin α is a mammalian nuclear protein involved in cell proliferation and differentiation. Here, we carried out the first study of the methylation status of ProTα genomic sequences in cell lines during differentiation as well as in tumoral tissues. We found that there is hypermethylation in all cell lines analyzed with a pattern that is characteristic of each cell type revealing specific genomic reorganizations. The decrease of ProTα mRNA during differentiation was not accompanied by changes in the methylation status. Remarkably, we found that there is hypomethylation in gastrointestinal tumors when compared with the peritumoral tissue. The biological implications of these findings are discussed.