The control by respiration of the uptake of α-methyl glucoside in Escherichia coli K12

The uptake of methyl α-d-glucopyranoside (α-MG) by Escherichia coli K12 was decreased by the addition of substrates which stimulated the rate of oxygen consumption by the cells. The inhibition, which occurred only at non-saturating concentrations of α-MG, was not the result of a stimulation of the rate of exit of intracellular α-MG, and was abolished by the presence of carbonyl cyanide m-chlorophenylhydrazone or sodium azide. Since those drugs inhibit energy conservation at the respiratory chain and did not alter significantly the rate of oxygen consumption under the conditions for the assay of α-MG uptake, it appears that the inhibition of the transport system by respirable substrates is mediated by some form of energy derived from respiration.     

Antinociceptive and Met-enkephalin releasing effects of tachykinins and substance P fragments

Substance P (SP), physalaemin, SP4-11, SP5-11 and the SP5-11 analog DiMe-C7 induce an antinociceptive effect in rats after intraventricular administration. Other tachykinins and the N-terminal fragments of SP are inactive. All antinociceptive peptides increase the Met-enkephalin efflux from slices of rat periaqueductal gray matter and their antinociceptive potency is correlated with their capacity to release Met-enkephalin. The results, discussed in the light of current theories on different tachykinin receptors, suggest that the SP-P receptor subtype may be involved in the control of noxious stimulation elicited by SP at supraspinal levels.     

Concomitant regulation of hippocampal calcium antagonist receptors and calcium uptake by substance P

The interaction of various neuropeptides with calcium antagonist binding was investigated in rat hippocampus. Among the peptides examined Substance P selectively increased the binding of phenylalkylamine and dihydropyridine calcium antagonists; this action was receptor mediated. No effect was observed with Substance P in other brain areas and with neurotensin and met-enkephalin in all the areas examined. The modification in calcium antagonist binding is functionally paralleled by an area specific increase in voltage-dependent calcium uptake. These data suggest that in hippocampus Substance P may be an endogenous regulator of voltage sensitive calcium channels.     

Nuclear localization of TRK-A in liver cells

The liver represents a site of expression of neurotrophins and their receptors. We have characterized the expression and intracellular localization of the nerve growth factor (NGF) receptor, Trk-A, in liver cells in vivo and in vitro. In both normal and fibrotic liver tissue, Trk-A immunostaining was present in different cell types, including parenchymal cells and cells of the inflammatory infiltrate. In hepatocytes and activated stellate cells (HSC), Trk-A showed a predominant nuclear localization, both in the presence and absence of injury. In cultured HSC, Trk-A was found to be functional, because exposure of the cells to recombinant NGF resulted in stimulation of cell migration and activation of intracellular signaling pathways, including Ras-ERK and PI3K/Akt. Remarkably, in cultured HSC, Trk-A staining was found constitutively in the nucleus. In these cells, Trk-A could be stained only by antibodies directed against the intracellular domain but not by those recognizing the extracellular portion of Trk-A suggesting that the intracellular portion of the receptor is the major determinant of nuclear Trk-A staining. In contrast to HSC, freshly isolated hepatocytes did not show any nuclear localization of the intracellular portion of Trk-A. In pheocromocytoma cells, nuclear staining for Trk-A was not present in conditions of serum deprivation, but could be induced by exposure to NGF or to a mixture of soluble mediators. We conclude that nuclear localization of the intracellular domain of Trk-A is observed constitutively in liver cells such as HSC, while in other cell types it could be induced in response to soluble factors.     

Common and rare species respond to similar niche processes in macroinvertebrate metacommunities

Ecologists have long investigated why communities are composed of a few common species and many rare species. Most studies relate rarity to either niche differentiation among species or spatial processes. There is a parallel between these processes and the processes proposed to explain the structure of metacommunities. Based on a metacommunity perspective and on data on stream macroinvertebrates from different regions of Brazil, we answer two questions. 1) Are sets of common and rare species affected by similar niche and spatial processes? 2) How does the community composition of common and of rare species differ? The main hypothesis we test is that common species are mainly affected by environmental factors, whereas rare species are mostly influenced by dispersal limitation. We used variation partitioning to determine the proportion of variation explained by the environment and space in common and rare species matrices. Contrary to our expectations, evidence supported the idea that both common and rare species are affected mainly by environmental factors, even after controlling for the differing information content between common and rare species matrices. Moreover, the abundance of some common species is also a good predictor of variation in rare species matrices. Niche differences are unlikely to be the sole cause of patterns of rarity in these metacommunities. We suggest that sets of common and rare species react to similar major environmental gradients and that rare species also respond to processes that operate at a more fine‐grained spatial scale, particularly biotic interactions. We extend the view that species sorting is the dominant process structuring metacommunities and argue that future studies focusing on rarity would benefit from a metacommunity perspective.     

Lysosomal fusion and SNARE function are impaired by cholesterol accumulation in lysosomal storage disorders

The function of lysosomes relies on the ability of the lysosomal membrane to fuse with several target membranes in the cell. It is known that in lysosomal storage disorders (LSDs), lysosomal accumulation of several types of substrates is associated with lysosomal dysfunction and impairment of endocytic membrane traffic. By analysing cells from two severe neurodegenerative LSDs, we observed that cholesterol abnormally accumulates in the endolysosomal membrane of LSD cells, thereby reducing the ability of lysosomes to efficiently fuse with endocytic and autophagic vesicles. Furthermore, we discovered that soluble N‐ethylmaleimide‐sensitive factor attachment protein (SNAP) receptors (SNAREs), which are key components of the cellular membrane fusion machinery are aberrantly sequestered in cholesterol‐enriched regions of LSD endolysosomal membranes. This abnormal spatial organization locks SNAREs in complexes and impairs their sorting and recycling. Importantly, reducing membrane cholesterol levels in LSD cells restores normal SNARE function and efficient lysosomal fusion. Our results support a model by which cholesterol abnormalities determine lysosomal dysfunction and endocytic traffic jam in LSDs by impairing the membrane fusion machinery, thus suggesting new therapeutic targets for the treatment of these disorders.     

Viral fusion peptides and identification of membrane-interacting segments

Viral envelope glycoproteins promote infection by mediating fusion between viral and cellular membranes. Fusion occurs after dramatic conformational changes within fusion proteins, leading to the exposure of a short stretch of mostly apolar residues, termed the fusion peptide, which is presumed to insert into the membrane and initiate the fusion process. The typical global composition of fusion peptides, rich in hydrophobic but also in small amino acids such as alanine and glycine, was used here as bait to detect other peptidic segments that can insert into membranes. We so evidenced a similar composition in several cytotoxic peptides, which promote pore formation such as peptides involved in amyloidoses and hydrophobic alpha-hairpins of pore-forming toxins. It is suggested that the structural plasticity observed for several membrane active peptides can be conferred by this particular global amino acid composition, which could be thus used to predict such functional behavior from genome data.     

Heat stress and seasonal effects on reproduction in the dairy cow--a review

In dairy cows inseminated during the hot months of the year, there is a decrease in fertility. Different factors contribute to this situation; the most important are a consequence of increased temperature and humidity that result in a decreased expression of overt estrus and a reduction in appetite and dry matter intake. Heat stress reduces the degree of dominance of the selected follicle and this can be seen as reduced steroidogenic capacity of its theca and granulosa cells and a fall in blood estradiol concentrations. Plasma progesterone levels can be increased or decreased depending on whether the heat stress is acute or chronic, and on the metabolic state of the animal. These endocrine changes reduce follicular activity and alter the ovulatory mechanism, leading to a decrease in oocyte and embryo quality. The uterine environment is also modified, reducing the likelihood of embryo implantation. Appetite and dry matter intake are both reduced by heat stress thus prolonging the postpartum period of negative energy balance and increasing the calving-conception interval, particularly in high producing dairy cows. The utilization of cooling systems may have a beneficial effect on fertility but dairy cows cooled in this way are still unable to match the fertility achieved in winter. Recent studies suggest that the use of gonadotropins to induce follicular development and ovulation can decrease the severity of seasonal postpartum infertility in dairy cows.     

Gene characterization, analysis of expression and in vitro synthesis of dihydroflavonol 4-reductase from [Citrus sinensis (L.) Osbeck

Dihydroflavonol 4-reductase (DFR, EC 1.1.1.219) catalyzes the reduction of dihydroflavonols to leucoanthocyanins, a key "late" step in the biosynthesis of anthocyanins. In this study we showed that a strong reduction in DFR expression occurs in the non-red orange cultivar (Navel and Ovale) compared to that of the red orange (Tarocco) suggesting that the enzyme could be involved in the lack of production of anthocyanins. Therefore, we isolated and compared the cDNAs, the genomic clones, as well as the promoter regions of blood and blond orange dfrs. Our data revealed that the cDNA sequences of pigmented and non-pigmented orange DFRs were 100% homologous and contained a 1017 bp open reading frame which encodes a protein of 338 amino acid residues, corresponding to a molecular mass of 38010.76 Da, with a theoretical pI of 5.96. Moreover, we found that there were no significant differences in non-coding regions (introns and 5' upstream region) of dfr sequences. Southern blot analysis of genomic DNA indicated that dfr was present as a single copy gene in both cultivars. From these findings the low expression level of blond orange dfr, which might play a role in the phenotypic change from blood to blond orange, is thought to be the result of a likely mutation in a regulatory gene controlling the expression of dfr. In addition, here we reported the successful expression of orange DFR cDNAs leading to an active DFR enzyme which converts dihydroquercetin to leucoanthocyanidin, thus confirming the involvement of the isolated genes in the biosynthesis of anthocyanins. Moreover, as far as we know, this is the first report concerning the in vitro expression of DFR from fruit flesh whose biochemical properties might be very different from those of other plant organ DFRs.