Research articles

The Kuiper belt is a remnant of the primordial Solar System. Small, sub-kilometre-sized, Kuiper belt objects elude direct detection, but the signature of their occultations of background stars should be detectable. Analysis of archival data now reveals an occultation by a body with an approximately 500-metre radius at a distance of 45 astronomical units. The detection of only one event reveals a deficit of sub-kilometre-sized Kuiper belt objects and implies that these small bodies are undergoing collisional erosion.

Feedback is one of the most powerful techniques for the control of classical systems. An extension into the quantum domain is desirable as it could allow the production of non-trivial quantum states and protection against decoherence. Here, real-time feedback control of the motion of a single atom trapped in an optical cavity is demonstrated, by using individual probe photons carrying information about the atomic position to activate a dipole laser.

A population of extrasolar planets has been uncovered with minimum masses of 1.9–10 times the Earth's mass, called super-Earths, but atmospheric studies can be precluded by the distance and size of their stars. Here, observations of the transiting planet GJ 1214b are reported; it has a mass 6.55 times that of the Earth and a radius 2.68 times the Earth's radius. The star is small and only 13 parsecs away, permitting the study of the planetary atmosphere with current observatories.

The activating E2f transcription factors induce transcription and drive cells out of quiescence, but whether activating E2fs are necessary for normal division is an area of debate. Here, the mouse retina is genetically manipulated to address E2f function in normal cells in vivo. Cells in the mouse retina can still divide in the absence of E2f1–3, although loss of activating E2fs leads to elevated apoptosis; thus, E2fs are not universally required for normal mammalian cell division.

A number of lines of evidence suggest that some crustal faults are weak compared to laboratory measurements of frictional strength; however, a satisfactory explanation for this weakness has remained elusive. Laboratory evidence is now provided for a brittle, frictional weakening mechanism based on common fault zone fabrics. Fault samples with well-developed foliation are shown to be extremely weak compared to their powdered equivalents.

The effect of sequence variants on phenotypes may depend on parental origin. Here, a method is developed that takes parental origin — the impact of which, to date, has largely been ignored — into account in genome-wide association studies. For 38,167 Icelanders genotyped, the parental origin of most alleles is determined; furthermore, a number of variants are found that show associations specific to parental origin, including three with type 2 diabetes.

The protein encoded by the breast cancer susceptibility gene BRCA1 participates in the DNA damage response and acts as a ubiquitin ligase; however, its regulation remains poorly understood. The ligase activity of BRCA1 is now shown to require PIAS-mediated modification with SUMO, and in the absence of PIAS SUMO ligases, DNA repair is impeded. The data demonstrate that the SUMOylation pathway has a significant role in the mammalian DNA damage response.

Sea levels during the last interglacial stage (about 125 kyr ago) are known to have been higher than today, and may serve as a partial analogue for anthropogenic warming scenarios. However, because local sea levels differ from global sea level, accurately reconstructing past global sea level requires an integrated analysis of globally distributed data sets. An extensive compilation of local sea level indicators and a statistical approach are now used to estimate global sea level during the last interglacial.

The quantitative description of microbial growth using a few measurable parameters is an important challenge in systems biology. Extracellular glucose sensing and uptake initiate the budding yeast's growth on glucose, but conventional growth models focus almost exclusively on glucose uptake. By uncoupling these two parameters, the interaction between glucose perception and import, rather than their individual actions, is now shown to determine the central features of growth.

Following the formation of a DNA double-strand break (DSB), cells activate the DNA-damage response and recruit a number of proteins to the lesion. Some of these proteins are modified by the attachment of small ubiquitin-related modifier (SUMO). Here, SUMO1, SUMO2 and SUMO3 are shown to accumulate at DSB sites in mammalian cells. SUMO1 and SUMO2/3 accrual requires the E3 ligase enzymes PIAS4 and PIAS1, which promote DSB repair.

The in vivo function of E2f transcription factors has been a matter of debate. The effects of E2f1, E2f2 and E2f3 triple deficiency are now examined in murine embryonic stem cells, embryos and small intestines. E2f1–3 are shown to function as transcriptional activators in normal dividing progenitor cells; however, contrary to the current view, they are dispensable for cell division but are necessary for cell survival.

Most schemes for three-dimensional (3D) structure determination of an object require multiple measurements over various orientations, or a means of scanning it section by section. A 3D imaging modality, termed ankylography, is now presented that under certain circumstances enables complete 3D structure determination from a single diffraction measurement. This approach could find broad applications in the physical and life sciences.

Here, the genomes of a malignant melanoma and a lymphoblastoid cell line from the same person are sequenced, providing the first comprehensive catalogue of somatic mutations from an individual cancer. The data provide insight into the causes of tumour formation and the development of the cancer genome, with the dominant mutational signature reflecting DNA damage due to ultraviolet light exposure.

Tobacco smoke contains more than sixty carcinogens that bind and mutate DNA. Here, massively parallel sequencing technology is used to sequence a small-cell lung cancer cell line, exploring the mutational burden associated with tobacco smoking. Multiple mutation signatures from the cocktail of carcinogens in tobacco smoke are found, as well as evidence of transcription-coupled repair and another, more general, expression-linked repair pathway.

Why hosts of brood parasites generally fail to recognize parasitic offspring after they have hatched from the egg, even when the host and parasitic chicks are very different, remains a puzzle. American coots are now shown to use first-hatched chicks in a brood as referents to learn to recognize their own chicks and discriminate against later-hatched parasitic chicks. A lack of reliable information may explain why the evolution of such chick recognition is not more common.

Sister chromatids are generally assumed to be genetically and functionally identical, with segregation to daughter cells being a random process; however, some evidence contradicts both of these assumptions. A technique is now developed to observe chromatid segregation in mitotic cells in vivo. Whereas many sister chromatids appeared to be randomly distributed between daughter cells, non-random sister chromatid segregation is observed in a subset of cells.

Over the past decade, several techniques have been developed to improve the detection of small amounts of DNA and RNA molecules, but detection of DNA molecules at concentrations below the femtomolar level requires amplified detection schemes. A unique nanomechanical response of hybridized DNA and RNA molecules that serves as an intrinsic molecular label is now reported; nanomechanical measurements allow direct detection and counting of hybridized molecules.

Expression of the embryonic M2 isoform of pyruvate kinase (PKM2) by tumour cells promotes aerobic glycolysis, whereas the normal adult isoform, PKM1, promotes oxidative phosphorylation. Expression of these isoforms is regulated by alternative splicing; here, aberrant expression of three heterogeneous nuclear ribonucleoprotein splicing factors, which are themselves regulated by the c-Myc oncogene, is shown to be responsible for the M1 to M2 switch in cancer.

Here, a draft sequence of the giant panda genome is assembled using next-generation sequencing technology alone. Genome analysis reveals a low divergence rate in comparison with dog and human genomes and insights into panda-specific traits; for example, the giant panda's bamboo diet may be more dependent on its gut microbiome than its own genetic composition.

Dendritic spines carry the majority of excitatory synapses, and spine morphology and distribution are critical for synaptic transmission, synaptic integration and plasticity. Here, signalling by the secreted semaphorin Sema3F is shown to control spine distribution along select dendritic processes, and distinct secreted semaphorin signalling events orchestrate CNS connectivity through the differential control of a variety of processes.