Research articles

Madagascar has a striking and peculiar fauna. It has been proposed that the ancestors of Madagascar's present-day mammal stock rafted there from Africa, but the validity of this hypothesis is questioned. Using palaeogeographic reconstructions and palaeo-oceanographic modelling, surface currents during the Palaeogene period are now shown to have been capable of transporting the animals to the island, as required by the hypothesis.

Sperm can increase their swimming velocity and gain a competitive advantage over sperm from another male by forming cooperative groups, such that selection should favour cooperation of the most closely related sperm. Sperm of deer mice are now shown to aggregate more often with conspecific than heterospecific sperm, in accordance with this theory, whereas in a monogamous species lacking sperm competition, sperm indiscriminately group with unrelated conspecific sperm.

Rodents have an orientation map of their surroundings, produced and updated by a network of neurons in the entorhinal cortex known as 'grid cells'. However, it is currently unknown whether humans encode their location in a similar manner. Using functional magnetic resonance imaging in humans, a macroscopic signal representing a subject's position in a virtual reality environment is now detected that meets the criteria for defining grid-cell encoding.

Progenitor cells sustain the capacity of self-renewing tissues for proliferation while suppressing cell cycle exit and terminal differentiation. DNA methylation is one potential epigenetic mechanism for the cellular memory needed to preserve the somatic progenitor state through cell divisions. The DNA methyltransferase 1 and other regulators of DNA methylation are now shown to be essential for epidermal progenitor cell function.

High mutation rates in the influenza A virus facilitate the generation of viral escape mutants, rendering vaccines and drugs potentially ineffective, but targeting host cell determinants could prevent viral escape. Here, 287 human host cell genes influencing influenza A virus replication are found using a genome-wide RNA interference screen. An independent assay is then used to investigate overlap between genes necessary for different viral strains.

Much of the mammalian genome is derived from retroelements, a significant proportion of which are endogenous retroviruses (ERVs). ERVs are transcriptionally silenced during early embryogenesis by histone and DNA methylation, but the initiators of this process are largely unknown. Here, deletion of KAP1 is shown to lead to a marked upregulation of a range of ERVs in mouse embryonic stem cells and in early embryos.

The close binary Algol system contains a radio-bright KIV sub-giant star in a very close and rapid orbit with a main sequence B8 star. Evidence points to the existence of an extended, complex coronal magnetosphere originating at the cooler K subgiant, but the detailed morphology of the subgiant's corona and its possible interaction with its companion are unknown. Multi-epoch radio imaging of the Algol system now reveals a large coronal loop suggestive of a persistent asymmetric magnetic field structure aligned between the two stars.

The properties of 'dwarf' galaxies have long challenged the cold dark matter (CDM) model of galaxy formation, as the properties of most observed dwarf galaxies contrast with models based on the dominance of CDM. Here, hydrodynamical simulations (assuming the presence of CDM) are reported in which the analogues of dwarf galaxies — bulgeless and with shallow central dark-matter profiles — arise naturally.

The elevation of the Tibetan plateau is thought to cause its surface to serve as a heat source that drives the South Asian summer monsoon, potentially coupling uplift of the plateau to climate changes on geologic timescales. Here, however, an atmospheric model is used to show that flattening of the Tibetan plateau has little effect on the monsoon, provided that the narrow orography of the Himalayas and adjacent mountain ranges is preserved.

Soybean is an important crop plant, providing seed protein and oil and fixing atmospheric nitrogen through symbioses with soil-borne microorganisms. Using a whole-genome shotgun approach, its 1.1-gigabase genome is now sequenced and integrated with physical and high-density genetic maps to create a chromosome-scale draft sequence assembly.

Polycomb proteins have a key role in regulating the expression of genes essential for development, differentiation and maintenance of cell fates. Here, Polycomb repressive complex 2 (PRC2) is shown to form a complex with JARID2, a Jumonji domain protein. JARID2 is required for the binding of Polycomb proteins to target genes in embryonic stem cells as well as for the proper differentiation of ES cells.

Form I Rubisco, one of the most abundant proteins in nature, catalyses the fixation of atmospheric CO₂ in photosynthesis. The limited catalytic efficiency of Rubisco has sparked extensive efforts to re-engineer the enzyme to enhance agricultural productivity. To bring this goal closer, the formation of cyanobacterial form I Rubisco is now analysed by in vitro reconstitution and cryo-electron microscopy.

Phytochromes regulate numerous photoresponses in plants and microorganisms through their ability to photointerconvert between a red-light-absorbing, ground state (Pf) and a far-red-light-absorbing, photoactivated state (Pfr). The structures of several phytochromes as Pf have been determined previously; here, the three-dimensional solution structure of the bilin-binding domain as Pfr is described. The results shed light on the structural basis for photoconversion to the activated Pfr form.

Rho is a general transcription termination factor in bacteria, but the mechanism by which it disrupts the RNA polymerase (RNAP) elongation complex is unknown. Here, Rho is shown to bind tightly to the RNAP throughout the transcription cycle, with the formation of the RNAP–Rho complex being crucial for termination. Furthermore, RNAP is proposed to have an active role in Rho termination through an allosteric mechanism.

The involvement of astroglia in long-term potentiation (LTP) of synaptic transmission remains controversial. Clamping internal Ca²⁺ in individual astrocytes in the CA1 area of the hippocampus is now shown to block LTP induction at nearby excitatory synapses through an effect on the N-methyl-D-aspartate receptor. This LTP blockade can be reversed by exogenous D-serine, normally released in a Ca²⁺-dependent manner from astrocytes.

Little is known about the recent evolution of the Y chromosome because only the human Y chromosome has been fully sequenced. The sequencing of the male-specific region of the Y chromosome (MSY) in the chimpanzee and comparison between the MSYs of the two species now reveals that they differ radically in sequence structure and gene content, indicating rapid evolution over the past 6 million years.

In human tumours, complex cell interactions in the tumour and its microenvironment are thought to have an important role in tumorigenesis and cancer progression. In a genetically well-defined model system in Drosophila, clones of cells bearing different mutations are now shown to cooperate to promote tumour growth and invasion. This interaction involves JNK signalling propagation and JNK-induced upregulation of JAK/STAT-activating cytokines.

Distinguishing self from non-self is a vital function for immune systems to repel invaders without inducing autoimmunity. One system, which protects bacteria and archaea from invasion by phage and plasmid DNA, involves clustered, regularly interspaced, short palindromic repeat (CRISPR) loci. Here, in Staphylococcus epidermidis, the mechanism of CRISPR self/non-self discrimination is defined.

GNF-2 is a recently discovered, selective allosteric Bcr–Abl inhibitor. Solution NMR, X-ray crystallography, mutagenesis and hydrogen exchange mass spectrometry are now used to show that GNF-2 binds to the myristate-binding site of Abl, leading to changes in the structural dynamics of the ATP-binding site. The results show that the combination of allosteric and ATP-competitive inhibitors can overcome resistance to either agent alone.

Immune homeostasis relies on tight control over the size of a population of regulatory T cells (T_reg) that can suppress over-exuberant immune responses. Cells commit to the T_reg lineage by upregulating the transcription factor Foxp3. Conserved non-coding DNA sequence elements at the Foxp3 locus are now shown to control the composition, size and maintenance of the T_reg cell population.