Routes and machinery of primary cilium biogenesis

Primary cilia are solitary, microtubule-based protrusions of the cell surface that play fundamental roles as photosensors, mechanosensors and biochemical sensors. Primary cilia dysfunction results in a long list of developmental and degenerative disorders that combine to give rise to a large spectrum of human diseases affecting almost any major body organ. Depending on the cell type, primary ciliogenesis is initiated intracellularly, as in fibroblasts, or at the cell surface, as in renal polarized epithelial cells. In this review, we have focused on the routes of primary ciliogenesis placing particular emphasis on the recently described pathway in renal polarized epithelial cells by which the midbody remnant resulting from a previous cell division event enables the centrosome for initiation of primary cilium assembly. The protein machinery implicated in primary cilium formation in epithelial cells, including the machinery best known for its involvement in establishing cell polarity and polarized membrane trafficking, is also discussed.     

Temporal precision in the neural code and the timescales of natural vision

The timing of action potentials relative to sensory stimuli can be precise down to milliseconds in the visual system, even though the relevant timescales of natural vision are much slower. The existence of such precision contributes to a fundamental debate over the basis of the neural code and, specifically, what timescales are important for neural computation. Using recordings in the lateral geniculate nucleus, here we demonstrate that the relevant timescale of neuronal spike trains depends on the frequency content of the visual stimulus, and that 'relative', not absolute, precision is maintained both during spatially uniform white-noise visual stimuli and naturalistic movies. Using information-theoretic techniques, we demonstrate a clear role of relative precision, and show that the experimentally observed temporal structure in the neuronal response is necessary to represent accurately the more slowly changing visual world. By establishing a functional role of precision, we link visual neuron function on slow timescales to temporal structure in the response at faster timescales, and uncover a straightforward purpose of fine-timescale features of neuronal spike trains.     

CACP, encoding a secreted proteoglycan, is mutated in camptodactyly-arthropathy-coxa vara-pericarditis syndrome.

Altered growth and function of synoviocytes, the intimal cells which line joint cavities and tendon sheaths, occur in a number of skeletal diseases. Hyperplasia of synoviocytes is found in both rheumatoid arthritis and osteoarthritis, despite differences in the underlying aetiologies of the two disorders. We have studied the autosomal recessive disorder camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP; MIM 208250) to identify biological pathways that lead to synoviocyte hyperplasia, the principal pathological feature of this syndrome. Using a positional-candidate approach, we identified mutations in a gene (CACP) encoding a secreted proteoglycan as the cause of CACP. The CACP protein, which has previously been identified as both 'megakaryocyte stimulating factor precursor' and 'superficial zone protein', contains domains that have homology to somatomedin B, heparin-binding proteins, mucins and haemopexins. In addition to expression in joint synovium and cartilage, CACP is expressed in non-skeletal tissues including liver and pericardium. The similarity of CACP sequence to that of other protein families and the expression of CACP in non-skeletal tissues suggest it may have diverse biological activities.     

The avian nature of the brain and inner ear of Archaeopteryx

Archaeopteryx, the earliest known flying bird (avialan) from the Late Jurassic period, exhibits many shared primitive characters with more basal coelurosaurian dinosaurs (the clade including all theropods more bird-like than Allosaurus), such as teeth, a long bony tail and pinnate feathers. However, Archaeopteryx possessed asymmetrical flight feathers on its wings and tail, together with a wing feather arrangement shared with modern birds. This suggests some degree of powered flight capability but, until now, little was understood about the extent to which its brain and special senses were adapted for flight. We investigated this problem by computed tomography scanning and three-dimensional reconstruction of the braincase of the London specimen of Archaeopteryx. Here we show the reconstruction of the braincase from which we derived endocasts of the brain and inner ear. These suggest that Archaeopteryx closely resembled modern birds in the dominance of the sense of vision and in the possession of expanded auditory and spatial sensory perception in the ear. We conclude that Archaeopteryx had acquired the derived neurological and structural adaptations necessary for flight. An enlarged forebrain suggests that it had also developed enhanced somatosensory integration with these special senses demanded by a lifestyle involving flying ability.     

Evidence for cultivar adoption and emerging complexity during the mid-Holocene in the La Plata basin

Multidisciplinary investigations at the Los Ajos archaeological mound complex in the wetlands of southeastern Uruguay challenge the traditional view that the La Plata basin was inhabited by simple groups of hunters and gatherers for much of the pre-Hispanic era. Here we report new archaeological, palaeoecological and botanical data indicating that during an increasingly drier mid-Holocene, at around 4,190 radiocarbon (14C) years before present (bp), Los Ajos became a permanent circular plaza village, and its inhabitants adopted the earliest cultivars known in southern South America. The architectural plan of Los Ajos during the following Ceramic Mound Period (around 3,000-500 14C yr bp) is similar to, but earlier than, settlement patterns demonstrated in Amazonia, revealing a new and independent architectural tradition for South America.     

A uniquely specialized ear in a very early tetrapod

The Late Devonian genus Ichthyostega was for many decades the earliest known tetrapod, and the sole representative of a transitional form between a fish and a land vertebrate. However, despite being known since 1932 (ref. 1) from a large collection of specimens, its morphology remained enigmatic and not what was expected of a very primitive tetrapod. Its apparent specializations led it to be considered as a "blind offshoot" or "sidebranch" off the tetrapod family tree, and recent cladistic analyses have disagreed about its exact phylogenetic position within the tetrapod stem group. In particular, its braincase and ear region defied interpretation, such that conventional anatomical terms seemed inapplicable. Using new material collected in 1998 (ref. 9), preparation of earlier-collected material, and high-resolution computed tomography scanning, here we identify and interpret these problematic anatomical structures. They can now be seen to form part of a highly specialized ear, probably a hearing device for use in water. This represents a structurally and functionally unique modification of the tetrapod otic region, unlike anything seen in subsequent tetrapod evolution. The presence of deeply grooved gill bars as in its contemporary Acanthostega suggest that Ichthyostega may have been more aquatically adapted than previously believed.     

Subthreshold Na+-dependent theta-like rhythmicity in stellate cells of entorhinal cortex layer II

The oscillation of membrane potential in mammalian central neurons is of interest because it relates to the role of oscillations in brain function. It has been proposed that the entorhinal cortex (EC), particularly the stellate cells of layer II (ECIIscs), plays an important part in the genesis of the theta rhythm. These neurons occupy a key position in the neocortex-hippocampus-neocortex circuit, a crucial crossroad in memory functions. Neuronal oscillations typically rely on the activation of voltage-dependent Ca2+ conductances and the Ca2+ -dependent K+ conductance that usually follows, as seen in other limbic subcortical structures generating theta rhythmicity. Here we report, however, that similar oscillations are generated in ECIIscs by a Na+ conductance. The finding of a subthreshold, voltage-gated, Na+ -dependent rhythmic membrane oscillation in mammalian neurons indicates that rhythmicity in heterogeneous neuronal networks may be supported by different sets of intrinsic ionic mechanisms in each of the neuronal elements involved.     

Action of tobacco on lipolysis and its modification by insulin

Resumen Los fumadores habituales tienen niveles de FFA significantivamente más altos que los no fumadores. El acto de fumar incrementa la lipolisis. Fumar sin inhalar el humo produce incremento de lipolisis. La insulina inhibe la accion lipolítica del humo de tabaco.