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International audience; In all vertebrates, invariant left/right (L/R) positioning and organization of the internal viscera is controlled by a conserved pathway. Nodal, a member of the TGFbeta superfamily is a critical upstream component responsible for initiating L/R axis determination. Asymmetric Nodal expression in the node preceeds and foreshadows morphological L/R asymmetry. Here we address the mechanism of Nodal activation in the left LPM by studying the function of a novel enhancer element, the AIE. We show this element is exclusively active in cells of the left lateral plate mesoderm (LPM) and is not itself responding to Nodal asymmetry. To test the hypothesis that this element may initiate asymmetric Nodal expression in the LPM, we deleted it from the mouse germ line. Mice homozygous for the AIE deletion (Nodal(deltaaie/deltaaie)) show no defects. However, we find that the AIE contributes to regulating the level of asymmetric Nodal activity; analysis of transheterozygous embryos (Nodal(deltaaie/null)) shows reduced Nodal expression in the left LPM associated with a low penetrance of L/R defects. Our findings point to the existence of two independent pathways that control Nodal expression in the left LPM.

International audience; The aim of this study was to compare magnetic resonance imaging (MRI) and histological estimates of the mean vessel diameter (mVD), the vessel density (Density), and the vessel size index (VSI) obtained in the same tumor-bearing animals. Twenty-seven rats bearing intracranial glioma (C6 or RG2) were imaged by MRI. Changes in transverse relaxations (ΔR 2* and R(2)) were induced by the injection of an iron-based contrast agent and were mapped using a multi gradient-echo spin-echo sequence. Then, brain vascular network was studied ex vivo by histology. Three regions of interest were drawn in apparently normal tissue (neocortex and striatum) and in the tumor. In vivo mVD(MRI), Density(MRI), and VSI(MRI) were measured; ex vivo, mVD(histo), Density(histo), and VSI(histo) were quantified on the same animals. MRI and histology measurements differed by -15 to 26%. A positive correlation was found between MRI and histology for mVD, Density, and VSI counterparts (R(2) = 0.62, 0.50, 0.73, respectively; P < 0.001 in all cases). This study indicates that MRI and histology yields well correlated the estimates of mVD, Density, and VSI. VSI is the closest MRI estimate to histology. As Density and mVD or VSI provide complementary information, it is worth computing them to characterize angiogenesis beyond blood volume fraction.

International audience; The role of hepatocyte apoptosis in the physiopathology of obstructive cholestasis is still controversial. Although some data have strongly suggested that hepatocellular cholestatic injury is due to Fas-mediated hepatocyte apoptosis, some others concluded that necrosis, rather than apoptosis, represents the main type of hepatocyte death in chronic cholestasis. Moreover, it has also been suggested that the reduced liver injury observed in the absence of Fas receptor after bile duct ligation was not due to lower hepatocyte apoptosis but to the indirect role of this receptor in non-hepatocytic cells such as cholangiocytes and inflammatory cells. The aim of this work was therefore to determine whether a protection against cell death limited to hepatocytes could be sufficient to reduce liver injury and delay cholestatic fibrosis. With this purpose, we performed bile duct ligation in transgenic mice overexpressing Bcl-2 in hepatocytes and in wild-type littermates. We found that, compared with necrosis, apoptosis was negligible in this model. Our results also showed that hepatocyte Bcl-2 expression protected hepatocytes against liver injury only in the early steps of the disease. This protection was correlated with reduced mitochondrial dysfunction and lipid peroxidation. However, in contrast to Fas receptor-deficient lpr mice, fibrosis progression was not hampered and liver inflammatory response was not reduced by Bcl-2 overexpression. These results therefore comfort the hypothesis that Fas-mediated apoptotic hepatocyte pathway is not a significant contributing factor to the clinical features observed in cholestasis. Moreover, in the absence of a blunted inflammatory response in transgenic mice, Bcl-2 protection against hepatocyte mitochondrial dysfunction and lipid peroxidation was not sufficient to block fibrosis progression.

Objective This study aims to evaluate the interest to systematically combine cytology and histology for all bone specimens. Methods We reviewed all the bone biopsies performed in the University Hospital of Brest, France, between January 2000 and March 2008 and for which cytology and histology, obtained at the same time, were available. The interest of cytology and histology, alone and in combination was studied in comparison with the diagnostic made by the practitioner who treated the patient, which was considered the reference. Results Seventy patients were included. Among them, 55 had a final diagnosis of cancer. Thirty-nine of them were identified either by cytology or histology: twenty-five were identified by the two techniques, eight only by histology, and six only by cytology. There was no false-positive result, but false-negative results occurred with cytology (n = 3) and histology (n = 4). The agreement malignancy/benignancy was high (κ = 0.84) between cytology and histology when taking into account the only contributive results. It dropped to 0.52 when taking into account all the samples. Conclusion Cytology and histology are complementary to each other in diagnosing bone lesion. Combining cytomorphology and tissue architecture increases the accuracy of bone sample and would systematically be performed for each bone biopsy.

http://www.pnas.org/content/102/22/7853.long; International audience; Tubulin is subject to a special cycle of detyrosination/tyrosination in which the C-terminal tyrosine of alpha-tubulin is cyclically removed by a carboxypeptidase and readded by a tubulin-tyrosine-ligase (TTL). This tyrosination cycle is conserved in evolution, yet its physiological importance is unknown. Here, we find that TTL suppression in mice causes perinatal death. A minor pool of tyrosinated (Tyr-)tubulin persists in TTL null tissues, being present mainly in dividing TTL null cells where it originates from tubulin synthesis, but it is lacking in postmitotic TTL null cells such as neurons, which is apparently deleterious because early death in TTL null mice is, at least in part, accounted for by a disorganization of neuronal networks, including a disruption of the cortico-thalamic loop. Correlatively, cultured TTL null neurons display morphogenetic anomalies including an accelerated and erratic time course of neurite outgrowth and a premature axonal differentiation. These anomalies may involve a mislocalization of CLIP170, which we find lacking in neurite extensions and growth cones of TTL null neurons. Our results demonstrate a vital role of TTL for neuronal organization and suggest a requirement of Tyr-tubulin for proper control of neurite extensions.

International audience; The Hnf4alpha gene belongs to a family of trancriptional regulators required for liver development and function. Hnf4alpha is also expressed in other tissues, including the newly formed visceral endoderm of the early postimplantation embryo, and later in embryogenesis in the gut epithelium and the kidney. The regulatory sequences involved in controlling expression of Hnf4alpha at these diverse sites are not clearly understood. Here we used homologous recombination to introduce Cre recombinase coding sequences into the endogenous Hnf4alpha locus. Crossing Hnf4alpha(Creex2/+) mice with R26R partners allowed us to follow the pattern of Cre-mediated recombination. Our results show that recombination of the reporter allele closely follows endogenous Hnf4alpha expression, but with a slight temporal delay. Thus, the Hnf4alpha(Creex2) strain should prove useful for conditionally deleting gene activity in the liver, gut epithelium, or kidney.