17 research outputs found
Põhihariduse ametliku korralduse areng eestis aastatel 1992–2012 põhikooli- ja gümnaasiumiseaduse muudatuste alusel ning lähteseis hariduskorralduse arenguks
http://tartu.ester.ee/record=b2694108~S1*es
Natural Occurrence of 2′,5′-Linked Heteronucleotides in Marine Sponges
2′,5′-oligoadenylate synthetases (OAS) as a component of mammalian interferon-induced antiviral enzymatic system catalyze the oligomerization of cellular ATP into 2′,5′-linked oligoadenylates (2-5A). Though vertebrate OASs have been characterized as 2′-nucleotidyl transferases under in vitro conditions, the natural occurrence of 2′,5′-oligonucleotides other than 2-5A has never been demonstrated. Here we have demonstrated that OASs from the marine sponges Thenea muricata and Chondrilla nucula are able to catalyze in vivo synthesis of 2-5A as well as the synthesis of a series 2′,5′-linked heteronucleotides which accompanied high levels of 2′,5′-diadenylates. In dephosphorylated perchloric acid extracts of the sponges, these heteronucleotides were identified as A2′p5′G, A2′ p5′U, A2′p5′C, G2′p5′A and G2′ p5′U. The natural occurrence of 2′-adenylated NAD+ was also detected. In vitro assays demonstrated that besides ATP, GTP was a good substrate for the sponge OAS, especially for OAS from C. nucula. Pyrimidine nucleotides UTP and CTP were also used as substrates for oligomerization, giving 2′,5′-linked homo-oligomers. These data refer to the substrate specificity of sponge OASs that is remarkably different from that of vertebrate OASs. Further studies of OASs from sponges may help to elucidate evolutionary and functional aspects of OASs as proteins of the nucleotidyltransferase family
Self-recognition and Ca2+-dependent carbohydrate–carbohydrate cell adhesion provide clues to the Cambrian explosion
Author Posting. © The Authors, 2009. This is the author's version of the work. It is posted here by permission of Oxford University Press for personal use, not for redistribution. The definitive version was published in Molecular Biology and Evolution 26 (2009): 2551-2561, doi:10.1093/molbev/msp170.The Cambrian explosion of life was a relatively short period ca. 540 million years ago that
marked a generalized acceleration in the evolution of most animal phyla, but the trigger of this
key biological event remains elusive. Sponges are the oldest extant Precambrian metazoan
phylum and thus a valid model to study factors that could have unleashed the rise of multicellular
animals. One such factor is the advent of self/non-self recognition systems, which would be
evolutionarily beneficial to organisms to prevent germ cell parasitism or the introduction of
deleterious mutations resulting from fusion with genetically different individuals. However, the
molecules responsible for allorecognition probably evolved gradually before the Cambrian
period, and some other (external) factor remains to be identified as the missing triggering event.
Sponge cells associate through calcium-dependent, multivalent carbohydrate-carbohydrate
interactions of the g200 glycan found on extracellular proteoglycans. Single molecule force
spectroscopy analysis of g200-g200 binding indicates that calcium affects the lifetime (+Ca/-Ca:
680 s/3 s) and bond reaction length (+Ca/-Ca: 3.47 Å/2.27 Å). Calculation of mean g200
dissociation times in low and high calcium within the theoretical framework of a cooperative
binding model indicates the non-linear and divergent characteristics leading to either
disaggregated cells or stable multicellular assemblies, respectively. This fundamental
phenomenon can explain a switch from weak to strong adhesion between primitive metazoan
cells caused by the well documented rise in ocean calcium levels at the end of Precambrian time.
We propose that stronger cell adhesion allowed the integrity of genetically uniform animals
composed only of “self” cells, facilitating genetic constitutions to remain within the metazoan
individual and be passed down inheritance lines. The Cambrian explosion might have been
triggered by the coincidence in time of primitive animals endowed with self/non-self recognition,
and of a surge in sea water calcium that increased the binding forces between their calcium-dependent cell adhesion molecules.D.A. and A.K. acknowledge financial support from the Collaborative Research
Center SFB 613 from the Deutsche Forschungsgemeinschaft (DFG), and X.F.-B. acknowledges
financial support from grants BIO2002-00128, BIO2005-01591, and CSD2006-00012 from the
Ministerio de Ciencia y Tecnología, Spain, which included Fondo Europeo de Desarrollo
Regional funds, and from grant 2005SGR-00037 from the Generalitat de Catalunya, Spain
Changes in metabolism of inorganic polyphosphate in rat tissues and human cells during development and apoptosis
Age-dependent studies show that the amount of inorganic polyphosphate in rat brain strongly increases after birth. Maximal levels were found in 12-months old animals. Thereafter, the concentration of total polyphosphate decreases to about 50%. This decrease in the concentration of total polyphosphate is due to a decrease in the amount of insoluble, long-chain polyphosphates. The amount of soluble, long-chain polyphosphates does not change significantly in the course of ageing. In rat embryos and newborns, mainly soluble polyphosphates could be detected. In rat liver, the age-dependent changes are less pronounced. The changes in polyphosphate level are accompanied by changes in exopolyphosphatase activity, which degrades the polymers to orthophosphate; highest enzyme activities were found when the polyphosphate level was low, Induction of apoptosis in the human leukemic cell line HL-60 by actinomycin D results in degradation of long polyphosphate chains. The total polyphosphate content does not change significantly in apoptotic cells