Slipping magnetic reconnection in coronal loops

Magnetic reconnection of solar coronal loops is the main process that causes solar flares and possibly coronal heating. In the standard model, magnetic field lines break and reconnect instantaneously at places where the field mapping is discontinuous. However, another mode may operate where the magnetic field mapping is continuous but shows steep gradients: The field lines may slip across each other. Soft x-ray observations of fast bidirectional motions of coronal loops, observed by the Hinode spacecraft, support the existence of this slipping magnetic reconnection regime in the Sun's corona. This basic process should be considered when interpreting reconnection, both on the Sun and in laboratory-based plasma experiments.     

Genome streamlining in a cosmopolitan oceanic bacterium

The SAR11 clade consists of very small, heterotrophic marine alpha-proteobacteria that are found throughout the oceans, where they account for about 25% of all microbial cells. Pelagibacter ubique, the first cultured member of this clade, has the smallest genome and encodes the smallest number of predicted open reading frames known for a free-living microorganism. In contrast to parasitic bacteria and archaea with small genomes, P. ubique has complete biosynthetic pathways for all 20 amino acids and all but a few cofactors. P. ubique has no pseudogenes, introns, transposons, extrachromosomal elements, or inteins; few paralogs; and the shortest intergenic spacers yet observed for any cell.     

Comparative genomics of trypanosomatid parasitic protozoa

A comparison of gene content and genome architecture of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major, three related pathogens with different life cycles and disease pathology, revealed a conserved core proteome of about 6200 genes in large syntenic polycistronic gene clusters. Many species-specific genes, especially large surface antigen families, occur at nonsyntenic chromosome-internal and subtelomeric regions. Retroelements, structural RNAs, and gene family expansion are often associated with syntenic discontinuities that-along with gene divergence, acquisition and loss, and rearrangement within the syntenic regions-have shaped the genomes of each parasite. Contrary to recent reports, our analyses reveal no evidence that these species are descended from an ancestor that contained a photosynthetic endosymbiont.     

Phosphorylation of retinoblastoma protein by viral protein with cyclin-dependent kinase function

As obligate intracellular parasites, viruses expertly modify cellular processes to facilitate their replication and spread, often by encoding genes that mimic the functions of cellular proteins while lacking regulatory features that modify their activity. We show that the human cytomegalovirus UL97 protein has activities similar to cellular cyclin-cyclin-dependent kinase (CDK) complexes. UL97 phosphorylated and inactivated the retinoblastoma tumor suppressor, stimulated cell cycle progression in mammalian cells, and rescued proliferation of Saccharomyces cerevisiae lacking CDK activity. UL97 is not inhibited by the CDK inhibitor p21 and lacks amino acid residues conserved in the CDKs that permit the attenuation of kinase activity. Thus, UL97 represents a functional ortholog of cellular CDKs that is immune from normal CDK control mechanisms.     

Nest inheritance is the missing source of direct fitness in a primitively eusocial insect

Animals that cooperate with nonrelatives represent a challenge to inclusive fitness theory, unless cooperative behavior is shown to provide direct fitness benefits. Inheritance of breeding resources could provide such benefits, but this route to cooperation has been little investigated in the social insects. We show that nest inheritance can explain the presence of unrelated helpers in a classic social insect model, the primitively eusocial wasp Polistes dominulus. We found that subordinate helpers produced more direct offspring than lone breeders, some while still subordinate but most after inheriting the dominant position. Thus, while indirect fitness obtained through helping relatives has been the dominant paradigm for understanding eusociality in insects, direct fitness is vital to explain cooperation in P. dominulus.     

The neural basis of economic decision-making in the Ultimatum Game

The nascent field of neuroeconomics seeks to ground economic decision making in the biological substrate of the brain. We used functional magnetic resonance imaging of Ultimatum Game players to investigate neural substrates of cognitive and emotional processes involved in economic decision-making. In this game, two players split a sum of money;one player proposes a division and the other can accept or reject this. We scanned players as they responded to fair and unfair proposals. Unfair offers elicited activity in brain areas related to both emotion (anterior insula) and cognition (dorsolateral prefrontal cortex). Further, significantly heightened activity in anterior insula for rejected unfair offers suggests an important role for emotions in decision-making.     

Phylogenomics: intersection of evolution and genomics

Much has been gained from genomic and evolutionary studies of species. Combining the perspectives of these different approaches suggests that an integrated phylogenomic approach will be beneficial.     

Unmasking the S-phase-promoting potential of cyclin B1

In higher eukaryotes, the S phase and M phase of the cell cycle are triggered by different cyclin-dependent kinases (CDKs). For example, in frog egg extracts, Cdk1-cyclin B catalyzes entry into mitosis but cannot trigger DNA replication. Two hypotheses can explain this observation: Either Cdk1-cyclin B fails to recognize the key substrates of its S-phase-promoting counterparts, or its activity is somehow regulated to prevent it from activating DNA synthesis. Here, we show that Cdk1-cyclin B1 has cryptic S-phase-promoting abilities that can be unmasked by relocating it from the cytoplasm to the nucleus and moderately stimulating its activity. Subcellular localization of vertebrate CDKs and the control of their activity are thus critical factors for determining their specificity.     

Recent biogenic phosphorite: concretions in mollusk kidneys

Phosphorite concretions have been detected in the kidneys of two widespread species of mollusks, Mercenaria mercenaria and Argopecten irradians, which have relatively high population densities. These concretions are the first documentation of the direct biogenic formation of phosphorite grains. The concretions are principally amorphous calcium phosphate, which upon being heated yields an x-ray diffraction pattern which is essentially that of chlorapatite. These concretions appear to be a normal formation of the excretory process of mollusks under reproductive, environmental, or pollutant-induced stress. Biogenic production of phosphorite concretions over long periods of time and diagenetic change from amorphous to crystalline structure, coupled with secondary enrichment, may account for the formation of some marine phosphorite desposits which are not easily explained by the chemical precipitation-replacement hypothesis.