1,721,085 research outputs found
The membrane permeability transition in liver mitochondria of the great green goby Zosterisessor ophiocephalus (pallas)
No full textLiver mitochondria from the great green goby Zosterisessor ophiocephalus (Pallas) normally exhibit bioenergetic variables (membrane potential 165+/-7 mV; respiratory control ratio 6.6+/-0.4; ADP/O ratio 1.85+/-0.8; means +/- s.e.m., N=6) and activities of physiological transport systems (phosphate/proton symporter, adenine nucleotide antiporter, Ca(2+) electrophoretic uniporter) comparable with those of rat liver mitochondria. When incubated in the presence of Ca(2+) and an inducer agent such as phosphate, these mitochondria undergo a complete collapse of membrane potential accompanied by a large-amplitude swelling of the matrix, influx of sucrose from the incubation medium, release of endogenous Mg(2+) and K(+) (approximately 90% of the total) and of preaccumulated Ca(2+) and oxidation of endogenous pyridine nucleotides. All these phenomena, which are completely eliminated by cyclosporin A and inhibited with different efficacies by Mg(2+) and spermine, demonstrate that the induction of the permeability transition in this type of mitochondria has characteristics similar to those described in rat liver mitochondria. In contrast, the requirement for very high Ca(2+) concentrations (greater than 100 micromol l(-1) for the induction of the permeability transition represents a very important difference that distinguishes this phenomenon in fish and mammalian mitochondria
What is hidden behind the concept of ecosystem efficiency in energy transformation?
No full textThe number of energy transformation levels in trophic webs is usually below five, but can be extended up to ten when parasites and hyper-parasites are included. Research on the structure and function of food webs is relevant to the complexity–stability–productivity debate. The aim of this theoretical analysis is to link energetic and connectional aspects of ecosystems with information theory. Updating an energetic model reported by Ricklefs [Ecologia, Zanichelli Editore S.p.A., Bologna, Italy, 1993, p. 896], our approach is integrated with a static analysis of food webs. The length of food webs is theoretically associated with the average ecological efficiency which can be empirically correlated with the effective connectance between species. Furthermore, the advantage of greater complexity when applied to a signalling network is qualitatively addressed.
The overall efficiency of energy transformation into biomass throughout a trophic web, in an ecosystem with a given number of species, is the resultant of the various ecological efficiencies, η, at the transitions between the trophic levels. However, we propose that an increment in effective connectance and interspecies connectivity based on a superimposed signalling web may increase the η values, despite the fact that signalling per se has an energetic cost. According to this hypothesis, ecosystem stability would not be necessarily reduced by increasing the number of trophic levels, N, whenever stability in terms of persistence is improved by a cost-efficient regulatory network
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Characterisation of three variants of estrogen receptor beta mRNA in the common sole, Solea solea L. (Teleostei).
No full textIn all vertebrates, estrogen action is mediated by cognate nuclear receptors. In this study, we cloned the different transcripts of the estrogen receptor beta (ERbeta) gene of the common sole, Solea solea. 5'-RLM-RACE (RNA Ligase-Mediated 5'-Rapid Amplification of cDNA Ends) and 3'-RACE analyses revealed three isoforms of different length, called Long, Intermediate and Short isoforms, consisting of 2212, 1531 and 1207 b, respectively. The Long isoform is characterised by an open reading frame (ORF) encoding 589aa, with an estimated molecular weight of 65kDa. Phylogenetic analysis established that it belongs to the teleost ERbeta1 or ERbetaa cluster. The Intermediate isoform encodes a 490-aa protein, which lacks the first 99aa of the Long isoform, but still retains a complete DNA-binding domain (DBD). In the Short variant (363aa-long), all the N-terminal region, down to the two zinc fingers included, is missing, thus crippling DBD. ERbeta transcription was analysed by semiquantitative RT-PCR with specific primers, common to the Long and Intermediate isoforms, in various sole tissues, such as brain, gills, muscle, stomach, intestine, spleen, head kidney, kidney, liver and gonads. This analysis revealed that ERbeta displays a widespread or ubiquitous pattern of transcription, with the highest levels being found in the gonads and liver
Tissue-specific transcriptional initiation of the CYP19 genes in rainbow trout, with analysis of splicing patterns and promoter sequences
No full textThe rainbow trout (Oncorhynchus mykiss Walbaum) genome contains three separate CYP19 genes for distinct isoforms of cytochrome P450arom: CYP19A encoding the prevalently ovarian isoform P450aromA, and CYP19B-I and II, encoding forms I and II of the mainly cerebral variant P450aromB. RNA Ligase-Mediated 5'-Rapid Amplification of cDNA Ends analysis was used to determine the 5'-untranslated terminal regions (5'-UTRs) of the corresponding mRNAs, which are actually all expressed in the ovary, brain and gills. CYP19A is transcribed at different transcription start sites (TSSs) in each tissue, the most distal TSS being found in the brain, the intermediate one in the gills, and the proximal one in the ovary. CYP19B-I also displays tissue-specific TSSs, but transcripts undergo three distinct splicing patterns: the same pattern as previously reported for the brain and occurring also in the gills, and two novel patterns, established in the ovary and brain, which include two cryptic 3'-splice sites in intron 1, leading to the inclusion of intronic sequences of 92/94 and 66 b in the 5'-UTRs. Lastly, the CYP19B-II transcript in the ovary shows the same splicing pattern previously described for the brain. A PCR-based gene walking strategy was used to explore the promoter regions of the rainbow trout CYP19 genes, which were found to contain potential binding sites for a variety of transcription factors
Regulatory regions in the promoter and third intron of the growth hormone gene in rainbow trout, Oncorhynchus mykiss Walbaum.
No full textThe mechanisms involved in the transcriptional regulation of the rainbow trout (Oncorhynchus mykiss) growth hormone (tGH) gene have been investigated. Transient transfection assays, using deletion mutants of the tGH promoter, demonstrated that the -226/+24 5'-flanking region, bearing three binding sites for the pituitary-specific transcription factor GHF1/Pit1 and a cAMP-response element, is necessary and sufficient to confer strong tissue-specific and cAMP-stimulated expression to a luciferase reporter gene. This region is also upregulated by the synthetic glucocorticoid dexamethasone (DEX), the combined effects of cAMP, and DEX being synergistic. Footprinting and gel shift assays revealed that GHF1 binds to a recognition element in the third intron of the tGH gene, suggesting that GHF1 can affect the expression of this gene by interacting with response elements in the transcription unit. These results may be exploited to design tGH gene constructs for the production of autotransgenic fish, in which the expression of the isospecific transgene driven by a constitutive proximal promoter is specifically targeted to the pituitary and physiologically controlled
Developmentally regulated expression and activity of 17a-hydroxylase/C-17,20 lyase cytochrome P450 (P450c17) in rat liver.
No full textWe have investigated the developmental pattern of expression and activity of 17 alpha-hydroxylase/C-17,20-lyase cytochrome P450 (cytochrome P450c17) in the liver, stomach, duodenum, and testis of rats from day 18 of pregnancy to adulthood. In the male liver, the enzyme became detectable at birth (135 pmol/mg protein.min) at a level comparable to that in the testis (188 pmol/mg protein.min). The activity then increased dramatically, reaching a peak at 8 days (691 pmol/mg protein.min), which was more than 4-fold the testicular levels in rats of the same age or in adults. Thereafter it declined steadily, becoming undetectable from puberty onward. The hepatic peak followed a depression in testicular activity (58 pmol/mg protein.min) on day 6. Northern and immunoblot analyses showed a good temporal correlation between enzyme activity and the occurrence of P450c17 messenger RNA (mRNA) and protein, The same patterns of mRNA and protein occurrence were observed in female rat liver, indicating that the hepatic CYP17 expression is not sexually dimorphic. Sequencing confirmed a complete identity in the coding region between hepatic and gonadal mRNAs. Hepatic P450c17 mRNA, however, was 150-200 bases longer than the gonadal counterparts. No significant expression of mRNAs encoding P450scc and P450arom was observed in liver of either sex at any age. In stomach and duodenum, enzyme activity was much lower (maxima at 25 and 14 pmol/mg protein.min, respectively) than that in liver, but persisted from the time of weaning onward. It is suggested that the hepatic peak in P450c17 activity may serve to convert circulating progestogens into androgens for gonadal aromatization during Sertoli and granulosa cell proliferation
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