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61.
Ribosomal RNA secondary structure: compensatory mutations and implications for phylogenetic analysis 总被引:6,自引:0,他引:6
Using sequence data from the 28S ribosomal RNA (rRNA) genes of selected
vertebrates, we investigated the effects that constraints imposed by
secondary structure have on the phylogenetic analysis of rRNA sequence
data. Our analysis indicates that characters from both base-pairing regions
(stems) and non-base-pairing regions (loops) contain phylogenetic
information, as judged by the level of support of the phylogenetic results
compared with a well-established tree based on both morphological and
molecular data. The best results (the greatest level of support of
well-accepted nodes) were obtained when the complete data set was used.
However, some previously supported nodes were resolved using either the
stem or loop bases alone. Stem bases sustain a greater number of
compensatory mutations than would be expected at random, but the number is
< 40% of that expected under a hypothesis of perfect compensation to
maintain secondary structure. Therefore, we suggest that in phylogenetic
analyses, the weighting of stem characters be reduced by no more than 20%,
relative to that of loop characters. In contrast to previous suggestions,
we do not recommend weighting of stem positions by one-half, compared with
that of loop positions, because this overcompensates for the constraints
that selection imposes on the secondary structure of rRNA.
相似文献
62.
Morphometric statistical techniques were used to investigate geometric aspects of 240 axodendritic presynaptic terminals (PT) located in the dorsal horn of the gray matter of the cat spinal cord. Parameters describing the configuration and average spatial radius of the three-dimensional PT (approximated by irregular ellipsoid were estimated on the basis of the morphometry of random PT sections applying aspects of the theory of probability. Lack of any correlation between location of the active zone and the configurational pattern (extent) of terminals was demonstrated. Densitometric distribution of average spatial PT radii was obtained (mean: 0.820 µm). The relatively limited scatter of this distribution would indicate extremely close similarity between parameters of the PT comprising the test group.Dnepropetrovsk University. A. A. Bogomolets Institute of Physiology, Academy of the Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 403–410, May–June, 1989. 相似文献
63.
Clara Correia‐Melo Francisco DM Marques Rhys Anderson Graeme Hewitt Rachael Hewitt John Cole Bernadette M Carroll Satomi Miwa Jodie Birch Alina Merz Michael D Rushton Michelle Charles Diana Jurk Stephen WG Tait Rafal Czapiewski Laura Greaves Glyn Nelson Mohammad Bohlooly‐Y Sergio Rodriguez‐Cuenca Antonio Vidal‐Puig Derek Mann Gabriele Saretzki Giovanni Quarato Douglas R Green Peter D Adams Thomas von Zglinicki Viktor I Korolchuk João F Passos 《The EMBO journal》2016,35(7):724-742
64.
A. B. Medvinsky A. V. Rusakov A. E. Bobyrev V. A. Burmensky A. E. Kriksunov N. I. Nurieva M. M. Gonik 《Biophysics》2009,54(1):90-93
A conceptual mathematical model of the dynamics of fish and zooplankton (rotifer) populations of connected lakes Naroch and Myastro (Belarus) is built and examined with parameters based on field data. It is shown that community coupling and trophic interactions give rise to both regular and irregular oscillations in population numbers. 相似文献
65.
In experimental learned helplessness in mice determined by preliminary inavoidable aversive exposure, activity of tricyclic antidepressants (desipramine, chlorimipramine, amitryptyline), type A MAO inhibitors (pyrazidol), and atypical (zimelidine, trazodon, befuralin) antidepressants as well as that of potential antidepressants (LIS-30, DZK-153) were determined upon chronic administration. The tricyclic compounds, befuralin and DZK-153 removed learned helplessness only after 14 days of administration. The substances with a predominant serotoninomimetic action (zimelidin, trazodon in high doses, pyrazidol, LIS-30) showed high efficacy following 6 days of administration. Single administration of the substances under study did not make it possible to disclose their specific antidepressant activity. 相似文献
66.
Thalhammer A Rudhard Y Tigaret CM Volynski KE Rusakov DA Schoepfer R 《The EMBO journal》2006,25(24):5873-5883
Excitatory synaptic transmission and plasticity are critically modulated by N-methyl-D-aspartate receptors (NMDARs). Activation of NMDARs elevates intracellular Ca(2+) affecting several downstream signaling pathways that involve Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). Importantly, NMDAR activation triggers CaMKII translocation to synaptic sites. NMDAR activation failed to induce Ca(2+) responses in hippocampal neurons lacking the mandatory NMDAR subunit NR1, and no EGFP-CaMKIIalpha translocation was observed. In cells solely expressing Ca(2+)-impermeable NMDARs containing NR1(N598R)-mutant subunits, prolonged NMDA application elevated internal Ca(2+) to the same degree as in wild-type controls, yet failed to translocate CaMKIIalpha. Brief local NMDA application evoked smaller Ca(2+) transients in dendritic spines of mutant compared to wild-type cells. CaMKIIalpha mutants that increase binding to synaptic sites, namely CaMKII-T286D and CaMKII-TT305/306VA, rescued the translocation in NR1(N598R) cells in a glutamate receptor-subtype-specific manner. We conclude that CaMKII translocation requires Ca(2+) entry directly through NMDARs, rather than other Ca(2+) sources activated by NMDARs. Together with the requirement for activated, possibly ligand-bound, NMDARs as CaMKII binding partners, this suggests that synaptic CaMKII accumulation is an input-specific signaling event. 相似文献
67.
Dendritic spines are protrusions from the dendritic shaft that host most excitatory synapses in the brain. Although they first emerge during neuronal maturation, dendritic spines remain plastic through adulthood, and recent advances in the molecular mechanisms governing spine morphology have shown them to be exquisitely sensitive to changes in the micro-environment. Among the many factors affecting spine morphology are components and regulators of the extracellular matrix (ECM). Modification of the ECM is critical to the repair of injuries throughout the body, including the CNS. Matrix metalloproteinase (MMP)-7/matrilysin is a key regulator of the ECM during pathogen infection, after nerve crush and in encephalitogenic disorders. We have investigated the effects of MMP-7 on dendritic spines in hippocampal neuron cultures and found that it induces the transformation of mature, short mushroom-shaped spines into long, thin filopodia reminiscent of immature spines. These changes were accompanied by a dramatic redistribution of F-actin from spine heads into thick, rope-like structures in the dendritic shaft. Strikingly, MMP-7 effects on dendritic spines were similar to those of NMDA treatment, and both could be blocked by channel-specific antagonists. These findings are the first direct evidence that MMPs can influence the morphology of mature dendritic spines, and hence synaptic stability. 相似文献
68.
69.