Identification of human brain tumour initiating cells

The cancer stem cell (CSC) hypothesis suggests that neoplastic clones are maintained exclusively by a rare fraction of cells with stem cell properties. Although the existence of CSCs in human leukaemia is established, little evidence exists for CSCs in solid tumours, except for breast cancer. Recently, we prospectively isolated a CD133+ cell subpopulation from human brain tumours that exhibited stem cell properties in vitro. However, the true measures of CSCs are their capacity for self renewal and exact recapitulation of the original tumour. Here we report the development of a xenograft assay that identified human brain tumour initiating cells that initiate tumours in vivo. Only the CD133+ brain tumour fraction contains cells that are capable of tumour initiation in NOD-SCID (non-obese diabetic, severe combined immunodeficient) mouse brains. Injection of as few as 100 CD133+ cells produced a tumour that could be serially transplanted and was a phenocopy of the patient's original tumour, whereas injection of 10(5) CD133- cells engrafted but did not cause a tumour. Thus, the identification of brain tumour initiating cells provides insights into human brain tumour pathogenesis, giving strong support for the CSC hypothesis as the basis for many solid tumours, and establishes a previously unidentified cellular target for more effective cancer therapies.     

Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs

How evolutionary changes in body size are brought about by variance in developmental timing and/or growth rates (also known as heterochrony) is a topic of considerable interest in evolutionary biology. In particular, extreme size change leading to gigantism occurred within the dinosaurs on multiple occasions. Whether this change was brought about by accelerated growth, delayed maturity or a combination of both processes is unknown. A better understanding of relationships between non-avian dinosaur groups and the newfound capacity to reconstruct their growth curves make it possible to address these questions quantitatively. Here we study growth patterns within the Tyrannosauridae, the best known group of large carnivorous dinosaurs, and determine the developmental means by which Tyrannosaurus rex, weighing 5,000 kg and more, grew to be one of the most enormous terrestrial carnivorous animals ever. T. rex had a maximal growth rate of 2.1 kg d(-1), reached skeletal maturity in two decades and lived for up to 28 years. T. rex's great stature was primarily attained by accelerating growth rates beyond that of its closest relatives.     

A new troodontid dinosaur from China with avian-like sleeping posture

Discovering evidence of behaviour in fossilized vertebrates is rare. Even rarer is evidence of behaviour in non-avialan dinosaurs that directly relates to stereotypical behaviour seen in extant birds (avians) and not previously predicted in non-avialan dinosaurs. Here we report the discovery of a new troodontid taxon from the Early Cretaceous Yixian Formation of western Liaoning, China. Numerous other three-dimensionally preserved vertebrate fossils have been recovered recently at this locality, including some specimens preserving behavioural information. The new troodontid preserves several features that have been implicated in avialan origins. Notably, the specimen is preserved in the stereotypical sleeping or resting posture found in extant Aves. Evidence of this behaviour outside of the crown group Aves further demonstrates that many bird features occurred early in dinosaurian evolution.     

C. elegans ORFeome version 1.1: experimental verification of the genome annotation and resource for proteome-scale protein expression

To verify the genome annotation and to create a resource to functionally characterize the proteome, we attempted to Gateway-clone all predicted protein-encoding open reading frames (ORFs), or the 'ORFeome,' of Caenorhabditis elegans. We successfully cloned approximately 12,000 ORFs (ORFeome 1.1), of which roughly 4,000 correspond to genes that are untouched by any cDNA or expressed-sequence tag (EST). More than 50% of predicted genes needed corrections in their intron-exon structures. Notably, approximately 11,000 C. elegans proteins can now be expressed under many conditions and characterized using various high-throughput strategies, including large-scale interactome mapping. We suggest that similar ORFeome projects will be valuable for other organisms, including humans.     

RecBCD enzyme is a bipolar DNA helicase

Escherichia coli RecBCD is a heterotrimeric helicase/nuclease that catalyses a complex reaction in which double-strand breaks in DNA are processed for repair by homologous recombination. For some time it has been clear that the RecB subunit possesses a 3' --> 5' DNA helicase activity, which was thought to drive DNA translocation and unwinding in the RecBCD holoenzyme. Here we show that purified RecD protein is also a DNA helicase, but one that possesses a 5' --> 3' polarity. We also show that the RecB and RecD helicases are both active in intact RecBCD, because the enzyme remains capable of processive DNA unwinding when either of these subunits is inactivated by mutation. These findings point to a bipolar translocation model for RecBCD in which the two DNA helicases are complementary, travelling with opposite polarities, but in the same direction, on each strand of the antiparallel DNA duplex. This bipolar motor organization helps to explain various biochemical properties of RecBCD, notably its exceptionally high speed and processivity, and offers a mechanistic insight into aspects of RecBCD function.     

Haem can bind to and inhibit mammalian calcium-dependent Slo1 BK channels

Haem is essential for living organisms, functioning as a crucial element in the redox-sensitive reaction centre in haemproteins. During the biogenesis of these proteins, the haem cofactor is typically incorporated enzymatically into the haem pockets of the apo-haemprotein as the functionally indispensable prosthetic group. A class of ion channel, the large-conductance calcium-dependent Slo1 BK channels, possesses a conserved haem-binding sequence motif. Here we present electrophysiological and structural evidence showing that haem directly regulates cloned human Slo1 channels and wild-type BK channels in rat brain. Both oxidized and reduced haem binds to the hSlo1 channel protein and profoundly inhibits transmembrane K+ currents by decreasing the frequency of channel opening. This direct regulation of the BK channel identifies a previously unknown role of haem as an acute signalling molecule.     

Evolutionary capacitance as a general feature of complex gene networks

An evolutionary capacitor buffers genotypic variation under normal conditions, thereby promoting the accumulation of hidden polymorphism. But it occasionally fails, thereby revealing this variation phenotypically. The principal example of an evolutionary capacitor is Hsp90, a molecular chaperone that targets an important set of signal transduction proteins. Experiments in Drosophila and Arabidopsis have demonstrated three key properties of Hsp90: (1) it suppresses phenotypic variation under normal conditions and releases this variation when functionally compromised; (2) its function is overwhelmed by environmental stress; and (3) it exerts pleiotropic effects on key developmental processes. But whether these properties necessarily make Hsp90 a significant and unique facilitator of adaptation is unclear. Here we use numerical simulations of complex gene networks, as well as genome-scale expression data from yeast single-gene deletion strains, to present a mechanism that extends the scope of evolutionary capacitance beyond the action of Hsp90 alone. We illustrate that most, and perhaps all, genes reveal phenotypic variation when functionally compromised, and that the availability of loss-of-function mutations accelerates adaptation to a new optimum phenotype. However, this effect does not require the mutations to be conditional on the environment. Thus, there might exist a large class of evolutionary capacitors whose effects on phenotypic variation complement the systemic, environment-induced effects of Hsp90.