Tuesday – day when four out of seven PLoS journals publish new articles and I pick a few most ‘bloggable’ ones to highlight here. As always, you should rate the articles, post notes and comments and send trackbacks when you blog about the papers. You can now also easily place articles on various social services (CiteULike, Mendeley, Connotea, Stumbleupon, Facebook and Digg) with just one click. Here are my own picks for the week – you go and look for your own favourites:
Cast shadows in visual scenes can have profound effects on visual perception. Much as they are informative, they also constitute noise as they are salient features of the visual scene potentially interfering with the processing of other features. Here we asked i) whether individuals with autism can exploit the information conveyed by cast shadows; ii) whether they are especially sensitive to noise aspects of shadows. Twenty high-functioning children with autism and twenty typically developing children were asked to recognize familiar objects while the presence, position, and shape of the cast shadow were systematically manipulated. Analysis of vocal reaction time revealed that whereas typically developing children used information from cast shadows to improve object recognition, in autistic children the presence of cast shadows–either congruent or incongruent–interfered with object recognition. Critically, vocal reaction times were faster when the object was presented without a cast shadow. We conclude that shadow-processing mechanisms are abnormal in autism. As a result, processing shadows becomes costly and cast shadows interfere rather than help object recognition.
In 2006 seven foreign ministers from Brazil, France, Indonesia, Norway, Senegal, South Africa, and Thailand initiated a dialogue on the inter-linkages between health and foreign policy, with a focus on how health matters to foreign policy and whether foreign policy can make a difference to health. What brought the ministers together was the realization that the state of global health has a profound impact on all nations and is deeply interconnected with trade and environment, economic growth, social development, national security, human rights, and dignity. These are challenges that go beyond the scope of ministries of health, and represent areas for which WHO (as the UN specialized agency for health) must have broader political support from member countries. Based on the ministers’ analysis, the Oslo Ministerial Declaration in 2007 stated a commitment to “make impact on health a defining lens that each of the countries would use to examine key elements of foreign policy and development strategies” . The ministers also decided to engage in a dialogue on how to deal with policy options from this perspective.
The body plan of all higher organisms develops during gastrulation. Gastrulation results from the integration of cell proliferation, differentiation and migration of thousands of cells. In the chick embryo gastrulation starts with the formation of the primitive streak, the site of invagination of mesoderm and endoderm cells, from cells overlaying Koller’s Sickle. Streak formation is associated with large-scale cell flows that carry the mesoderm cells overlying Koller’s sickle into the central midline region of the embryo. We use multi-cell computer simulations to investigate possible mechanisms underlying the formation of the primitive streak in the chick embryo. Our simulations suggest that the formation of the primitive streak employs chemotactic movement of a subpopulation of streak cells, as well as differential adhesion between the mesoderm cells and the other cells in the epiblast. Both chemo-attraction and chemo-repulsion between various combinations of cell types can create a streak. However, only one combination successfully reproduces experimental observations of the manner in which two streaks in the same embryo interact. This finding supports a mechanism in which streak tip cells produce a diffusible morphogen which repels cells in the surrounding epiblast. On the other hand, chemotactic interaction alone does not reproduce the experimental observation that the large-scale vortical cell flows develop simultaneously with streak initiation. In our model the formation of large scale cell flows requires an additional mechanism that coordinates and aligns the motion of neighboring cells.
Embryonic development is a four-dimensional process: in order to create an organism, the right genes must be expressed at the right time and in the right place. But while the overall strategy of embryogenesis is clear–successive waves of gene expression give rise to a pattern of transcription factors varying in time and space, driving cell differentiation–relatively little is known about the four-dimensional details of this process for most cell types. In a new study in this issue of PLoS Biology, Daniel Karlsson, Magnus Baumgardt, and Stefan Thor elucidate some of those details in the developing nervous system of the fly and show that major differences between body regions can arise from simple changes in gene expression.
Human rhinoviruses (HRVs) evolve rapidly due in part to their error-prone RNA polymerase. Knowledge of the diversity of HRV populations emerging during the course of a natural infection is essential and represents a basis for the design of future potential vaccines and antiviral drugs. To evaluate HRV evolution in humans, nasal wash samples were collected daily for five days from 15 immunocompetent volunteers experimentally infected with a reference stock of HRV-39. In parallel, HeLa-OH cells were inoculated to compare HRV evolution in vitro. Nasal wash in vivo assessed by real-time PCR showed a viral load that peaked at 48-72 h. Ultra-deep sequencing was used to compare the low-frequency mutation populations present in the HRV-39 inoculum in two human subjects and one HeLa-OH supernatant collected 5 days post-infection. The analysis revealed hypervariable mutation locations in VP2, VP3, VP1, 2C and 3C genes and conserved regions in VP4, 2A, 2B, 3A, 3B and 3D genes. These results were confirmed by classical sequencing of additional samples, both from inoculated volunteers and independent cell infections, and suggest that HRV inter-host transmission is not associated with a strong bottleneck effect. A specific analysis of the VP1 capsid gene of 15 human cases confirmed the high mutation incidence in this capsid region, but not in the antiviral drug-binding pocket. We could also estimate a mutation frequency in vivo of 3.4×10−4 mutations/nucleotides and 3.1×10−4 over the entire ORF and VP1 gene, respectively. In vivo, HRV generate new variants rapidly during the course of an acute infection due to mutations that accumulate in hot spot regions located at the capsid level, as well as in 2C and 3C genes.