Trak1 mutation disrupts GABA(A) receptor homeostasis in hypertonic mice

Hypertonia, which results from motor pathway defects in the central nervous system (CNS), is observed in numerous neurological conditions, including cerebral palsy, stroke, spinal cord injury, stiff-person syndrome, spastic paraplegia, dystonia and Parkinson disease. Mice with mutation in the hypertonic (hyrt) gene exhibit severe hypertonia as their primary symptom. Here we show that hyrt mutant mice have much lower levels of gamma-aminobutyric acid type A (GABA(A)) receptors in their CNS, particularly the lower motor neurons, than do wild-type mice, indicating that the hypertonicity of the mutants is likely to be caused by deficits in GABA-mediated motor neuron inhibition. We cloned the responsible gene, trafficking protein, kinesin binding 1 (Trak1), and showed that its protein product interacts with GABA(A) receptors. Our data implicate Trak1 as a crucial regulator of GABA(A) receptor homeostasis and underscore the importance of hyrt mice as a model for studying the molecular etiology of hypertonia associated with human neurological diseases.     

Identification and characterization of rod-derived cone viability factor

Retinitis pigmentosa is an untreatable, inherited retinal disease that leads to blindness. The disease initiates with the loss of night vision due to rod photoreceptor degeneration, followed by irreversible, progressive loss of cone photoreceptor. Cone loss is responsible for the main visual handicap, as cones are essential for day and high-acuity vision. Their loss is indirect, as most genes associated with retinitis pigmentosa are not expressed by these cells. We previously showed that factors secreted from rods are essential for cone viability. Here we identified one such trophic factor by expression cloning and named it rod-derived cone viability factor (RdCVF). RdCVF is a truncated thioredoxin-like protein specifically expressed by photoreceptors. The identification of this protein offers new treatment possibilities for retinitis pigmentosa.     

A bizarre predatory dinosaur from the Late Cretaceous of Madagascar

Here we report the discovery of a small-bodied (approximately 1.8 m) predatory dinosaur from the Late Cretaceous (Maastrichtian) of Madagascar. Masiakasaurus knopfleri, gen. et sp. nov., represented by several skull elements and much of the postcranial skeleton, is unique in being the only known theropod with a highly procumbent and distinctly heterodont lower dentition. Such a derived dental morphology is otherwise unknown among dinosaurs. Numerous skeletal characteristics indicate that Masiakasaurus is a member of Abelisauroidea, an enigmatic clade of Gondwanan theropods. Previously, small-bodied abelisauroids were known only from Argentina. The occurrence of Masiakasaurus on Madagascar suggests that small-bodied abelisauroids, like their larger-bodied counterparts, were more cosmopolitan, radiating throughout much of Gondwana and paralleling the diversification of small coelurosaur theropods in Laurasia.     

Unification, explanation, and the composition of causes in Newtonian mechanics

William Whewell's philosophy of scientific discovery is applied to the problem of understanding the nature of unification and explanation by the composition of causes in Newtonian mechanics. The essay attempts to demonstrate: (1) the sense in which ‘approximate’ laws (e.g. Kepler's laws of planetary motion) successfully refer to real physical systems rather than to (fictitious) idealizations of them; (2) why good theoretical constructs are not badly underdetermined by observation; and why, in particular, Newtonian forces are not conventional and (3) how empiricist arguments against the existence of component causes, and against the veracity of the fundamental laws, are flawed.     

禁带区域内负的群速度

研究超声波经过两个烧结样品的行为.两个烧结样品为有序的面心立方结构,它们的结构几乎相同.研究表明:在两个有序的准均匀的介质中分别有一个禁带区域.就禁带区域而言,在两个样品中产生禁带的区域非常接近.同时在禁带出现的区域群速度为负值.我们的结果表明群速度的负值的确存在于有序介质中的禁带区域内.     

High temperatures in the Late Cretaceous Arctic Ocean

To understand the climate dynamics of the warm, equable greenhouse world of the Late Cretaceous period, it is important to determine polar palaeotemperatures. The early palaeoceanographic history of the Arctic Ocean has, however, remained largely unknown, because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice. A shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated Upper Cretaceous organic-rich sediment from Alpha ridge, a submarine elevated feature of probable oceanic origin. A lack of carbonate in the sediments from this core has prevented the use of traditional oxygen-isotope palaeothermometry. Here we determine Arctic palaeotemperatures from these Upper Cretaceous deposits using TEX86, a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton, Crenarchaeota. From these analyses we infer an average sea surface temperature of approximately 15 degrees C for the Arctic Ocean about 70 million years ago. This calibration point implies an Equator-to-pole gradient in sea surface temperatures of approximately 15 degrees C during this interval and, by extrapolation, we suggest that polar waters were generally warmer than 20 degrees C during the middle Cretaceous (approximately 90 million years ago).