Archives de 16 juin 2008

Visualization of Cartilage Formation: Insight into Cellular Properties of Skeletal Progenitors and Chondrodysplasia Syndromes

Visualization of Cartilage Formation: Insight into Cellular Properties of Skeletal Progenitors and Chondrodysplasia Syndromes

Visualization of Cartilage Formation: Insight into Cellular Properties of Skeletal Progenitors and Chondrodysplasia Syndromes

Maria Barna and Lee Niswander

Developmental Cell, Volume 12, Issue 6, 5 June 2007, Pages 931-941

The cellular events underlying skeletal morphogenesis and the formation of cartilage templates are largely unknown. We generated an imaging system to dynamically visualize limb mesenchymal cells undergoing successive phases in cartilage formation and to delineate the cellular function of key regulators of chondrogenesis found mutated in chondrodysplasia syndromes. We uncovered an unsuspected role for Sox9 in control of cell morphology, independent from its major downstream target ColIIa, critically required for the mesenchyme-to-chondrocyte transition. In contrast, Bmp signaling regulates a cellular program we term “compaction” in which mesenchymal cells acquire a cohesive cell behavior required to delineate the boundaries and size of cartilage elements. Moreover, we visualized labeled progenitor cells from different regions of the limb bud and identified unique cellular properties that may direct their contribution toward specific skeletal elements such as the humerus or digits. These findings shed light on the cellular basis for chondrodysplasia syndromes and formation of the vertebrate skeleton.

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Genetic evidence that FGFs have an instructive role in limb proximal–distal patterning

Genetic evidence that FGFs have an instructive role in limb proximal–distal patterning

Francesca V. Mariani, Christina P. Ahn & Gail R. Martin
These authors contributed equally to this work.

Nature 453, 401-405 (15 May 2008) | doi:10.1038/nature06876

Half a century ago, the apical ectodermal ridge (AER) at the distal tip of the tetrapod limb bud was shown to produce signals necessary for development along the proximal–distal (P–D) axis, but how these signals influence limb patterning is still much debated. Fibroblast growth factor (FGF) gene family members are key AER-derived signals, with Fgf4, Fgf8, Fgf9 and Fgf17 expressed specifically in the mouse AER. Here we demonstrate that mouse limbs lacking Fgf4, Fgf9 and Fgf17 have normal skeletal pattern, indicating that Fgf8 is sufficient among AER-FGFs to sustain normal limb formation. Inactivation of Fgf8 alone causes a mild skeletal phenotype; however, when we also removed different combinations of the other AER-FGF genes, we obtained unexpected skeletal phenotypes of increasing severity, reflecting the contribution that each FGF can make to the total AER-FGF signal. Analysis of the compound mutant limb buds revealed that, in addition to sustaining cell survival, AER-FGFs regulate P–D-patterning gene expression during early limb bud development, providing genetic evidence that AER-FGFs function to specify a distal domain and challenging the long-standing hypothesis that AER-FGF signalling is permissive rather than instructive for limb patterning. We discuss how a two-signal model for P–D patterning can be integrated with the concept of early specification to explain the genetic data presented here.

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Seroprevalence of Trichinella, Toxoplasma, and Salmonella in Antimicrobial-Free and Conventional Swine Production Systems

Seroprevalence of Trichinella, Toxoplasma, and Salmonella in Antimicrobial-Free and Conventional Swine Production Systems

Wondwossen A. Gebreyes, Peter B. Bahnson, Julie A. Funk, James McKean, Prapas Patchanee. Foodborne Pathogens and Disease. April 1, 2008, 5(2): 199-203. doi:10.1089/fpd.2007.0071.

There has been a growing niche-market, outdoor, antimicrobial-free (ABF) swine production system in the last few years prompted by consumers’ demand for a more “natural” pork product. The impact of such production systems on reemergence of current and historically significant swine-associated pathogens has not been determined. The objectives of the current study were to determine and compare Salmonella, Toxoplasma, and Trichinella seropositivity in two swine production systems: outdoor ABF and intensive indoor production systems. These three foodborne pathogens represent those with the highest importance for pork consumption. A total of 675 serum samples from three participating states, Wisconsin, North Carolina, and Ohio, were investigated. We found significantly higher seroprevalence of Salmonella and Toxoplasma from ABF herds (54% and 7%, respectively) than conventional (39% and 1%, respectively) (p = 0.001). Two pigs, both from ABF herds, were found to be seropositive for Trichinella. The results from this preliminary study suggest that all three pathogens were more commonly present in pigs that were reared in an ABF, outdoor, niche-market type of environment than the conventional, indoor-reared herds though there were some geographical variation in Salmonella. This warrants a robust epidemiologic study to determine the role of various risk factors in the two production systems that may lead to persistence of bacterial (Salmonella) pathogens and reemergence of parasites (such as Trichinella) of historical significance.

Déjà que j’avais du mal à avaler des produits bio, je crois que je vais commencer à passer à distance des étals du marché de mon quartier 🙂 Sans blagues, je m’attendais à ce que pathogènes et parasites soient plus fréquents, mais pas à ce point. La séropositivité pour Trichinella passe de 1/7000 à 1/300 !

Bon, la situation n’est pas dramatique une fois la bête cuite, bien cuite, c’est avant que ça pourrait poser des problèmes. Donc, renfort des mesures d’hygiène et ça devrait aller, de ce point de vue au moins.

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Template-directed synthesis of a genetic polymer in a model protocell

Template-directed synthesis of a genetic polymer in a model protocell

Sheref S. Mansy, Jason P. Schrum, Mathangi Krishnamurthy, Sylvia Tobé, Douglas A. Treco & Jack W. Szostak

doi:10.1038/nature07018

Contemporary phospholipid-based cell membranes are formidable barriers to the uptake of polar and charged molecules ranging from metal ions to complex nutrients. Modern cells therefore require sophisticated protein channels and pumps to mediate the exchange of molecules with their environment. The strong barrier function of membranes has made it difficult to understand the origin of cellular life and has been thought to preclude a heterotrophic lifestyle for primitive cells. Although nucleotides can cross dimyristoyl phosphatidylcholine membranes through defects formed at the gel-to-liquid transition temperature, phospholipid membranes lack the dynamic properties required for membrane growth. Fatty acids and their corresponding alcohols and glycerol monoesters are attractive candidates for the components of protocell membranes because they are simple amphiphiles that form bilayer membrane vesicles that retain encapsulated oligonucleotides and are capable of growth and division. Here we show that such membranes allow the passage of charged molecules such as nucleotides, so that activated nucleotides added to the outside of a model protocell spontaneously cross the membrane and take part in efficient template copying in the protocell interior. The permeability properties of prebiotically plausible membranes suggest that primitive protocells could have acquired complex nutrients from their environment in the absence of any macromolecular transport machinery; that is, they could have been obligate heterotrophs.

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