Thoughts on the evolution of modern oceans

Explanation of the evolution of the Earth's oceans, particularly the processes involved in the generation of the oceans, are important for understanding the general appearance of our planet, and for the solution of specific problems. A comparative study of the world's oceans shows there is a single genetic series in the evolution of oceans, and that the oceans of the world are at different stages in their evolution. The Arctic Ocean, dated as Cenozoic, is noted for its small size and shallow oceanic floor, extensive but passive continental margins, limited volcanism, significant crustal thickness, and a lack of Benioff zones. The Mesozoic, Indian and Atlantic oceans have much greater dimensions and depths than the Arctic Ocean, the crust is thinner beneath them, volcanism is much more extensive, and active margins, while in the initial phase of evolution, are limited in extent. The area of the most ancient (probably Paleozoic) Pacific Ocean is equal to the sum of the rest of the three oceans; it also has the greatest oceanic depth. Beneath the Pacific, the crust is thinned and is characterized by high permeability, because of which magmatism is particularly widespread. Active continental margins arc also extensive in the Pacific. The concept of evolutionary development of the oceans enables us to predict the comparative potential of oceans with regards to their oil and gas and ore content. RÉSUMÉ Les explications de l'évolution des océans de la terre, particulièrement les processus impliqués dans la formation des océans, sont importants pour compréndre l'aspect général de notre planète et pour la solution de problèmes spécifiques. Une étude comparative des océans du monde montre qu'il y a une suite génétique unique dans l'évolution des océans, et que les océans du monde en sont a différents stades dans leur évolution. l'océan Arctique, datant du cénozoique, est caractérise par sa petite taille et son fond océanique peu profond, des marges continentales étendues mais passives, une petite quantité de volcanisme, une croûte épaisse, et une absence de zones de Benioff. Les océans Indien et Atlantique, mésozoiques, ont des dimensions et des profondeurs beaucoup plus grandes que celles de l'océan Arctique, la croute sous-jacente est plus mince; le volcanisme est beaucoup plus répandu, et les marges actives, dans leur phase initiate d'évolution, sont d'étendue limitée. La surface de l'océan Pacifique, le plus ancien (probablement paléozoique), est égale a la somme des trois autres océans; il a aussi la plus grande profondeur. Sous le Pacifique, la croûte est amincie et caractérisee par une grande perméabilité, en raison de laquelle le magmatisme est particulièrement repandu. Les marges continentales actives sont aussi abondantes dans le Pacifique. Le concept de l'évolution des océans nous permet de prédire le potentiel comparatif des océans en regard de leur contenu en pétrole, gaz naturel et minerai. [Traduit par la rédaction

Evolutionary Toggling of Vpx/Vpr Specificity Results in Divergent Recognition of the Restriction Factor SAMHD1

SAMHD1 is a host restriction factor that blocks the ability of lentiviruses such as HIV-1 to undergo reverse transcription in myeloid cells and resting T-cells. This restriction is alleviated by expression of the lentiviral accessory proteins Vpx and Vpr (Vpx/Vpr), which target SAMHD1 for proteasome-mediated degradation. However, the precise determinants within SAMHD1 for recognition by Vpx/Vpr remain unclear. Here we show that evolution of Vpx/Vpr in primate lentiviruses has caused the interface between SAMHD1 and Vpx/Vpr to alter during primate lentiviral evolution. Using multiple HIV-2 and SIV Vpx proteins, we show that Vpx from the HIV-2 and SIVmac lineage, but not Vpx from the SIVmnd2 and SIVrcm lineage, require the C-terminus of SAMHD1 for interaction, ubiquitylation, and degradation. On the other hand, the N-terminus of SAMHD1 governs interactions with Vpx from SIVmnd2 and SIVrcm, but has little effect on Vpx from HIV-2 and SIVmac. Furthermore, we show here that this difference in SAMHD1 recognition is evolutionarily dynamic, with the importance of the N- and C-terminus for interaction of SAMHD1 with Vpx and Vpr toggling during lentiviral evolution. We present a model to explain how the head-to-tail conformation of SAMHD1 proteins favors toggling of the interaction sites by Vpx/Vpr during this virus-host arms race. Such drastic functional divergence within a lentiviral protein highlights a novel plasticity in the evolutionary dynamics of viral antagonists for restriction factors during lentiviral adaptation to its hosts. © 2013 Fregoso et al

Differential Effects of Vpr on Single-cycle and Spreading HIV-1 Infections in CD4+ T-cells and Dendritic Cells

The Vpr protein of human immunodeficiency virus type 1 (HIV-1) contributes to viral replication in non-dividing cells, specifically those of the myeloid lineage. However, the effects of Vpr in enhancing HIV-1 infection in dendritic cells have not been extensively investigated. Here, we evaluated the role of Vpr during infection of highly permissive peripheral blood mononuclear cells (PBMCs) and CD4+ T-cells and compared it to that of monocyte-derived dendritic cells (MDDCs), which are less susceptible to HIV-1 infection. Infections of dividing PBMCs and non-dividing MDDCs were carried out with single-cycle and replication-competent HIV-1 encoding intact Vpr or Vpr-defective mutants. In contrast to previous findings, we observed that single-cycle HIV-1 infection of both PBMCs and MDDCs was significantly enhanced in the presence of Vpr when the viral stocks were carefully characterized and titrated. HIV-1 DNA quantification revealed that Vpr only enhanced the reverse transcription and nuclear import processes in single-cycle HIV-1 infected MDDCs, but not in CD4+ T-cells. However, a significant enhancement in HIV-1 gag mRNA expression was observed in both CD4+ T-cells and MDDCs in the presence of Vpr. Furthermore, Vpr complementation into HIV-1 virions did not affect single-cycle viral infection of MDDCs, suggesting that newly synthesized Vpr plays a significant role to facilitate single-cycle HIV-1 infection. Over the course of a spreading infection, Vpr significantly enhanced replication-competent HIV-1 infection in MDDCs, while it modestly promoted viral infection in activated PBMCs. Quantification of viral DNA in replication-competent HIV-1 infected PBMCs and MDDCs revealed similar levels of reverse transcription products, but increased nuclear import in the presence of Vpr independent of the cell types. Taken together, our results suggest that Vpr has differential effects on single-cycle and spreading HIV-1 infections, which are dependent on the permissiveness of the target cell