Biomedical subjects

Lucile Miquerol

Publications and source records attributed to Lucile Miquerol.

8 recordsLinked to original sources

PubMed2005

Discontinuous conduction in mouse bundle branches is caused by bundle-branch architecture.

BACKGROUND: Recordings of the electrical activity of mouse bundle branches (BBs) suggest reduced conduction velocity (CV) in the midseptal compared with the proximal part of the BB. The present study was performed to elucidate the mechanism responsible for this slowing of conduction. METHODS AND RESULTS: Hearts of 16 mice were isolated and Langendorff perfused. After the right and left ventricular free walls were removed, the extracellular activity of the BB was mapped with a 247-point electrode. Premature stimulation was used to estimate CV restitution in the BBs. Expression/distribution of connexin40 (Cx40), Cx43, and Cx45 was determined. Morphology of the conduction system was assessed by whole-mount acetylcholine esterase staining and in Cx40(+/KI-GFP) hearts. Effective CV in the midseptal part of the left and right BBs was reduced by 50% compared with the proximal BB. CV restitution in the proximal and midseptal parts of the BBs was similar. Myocytes labeled positive for Cx40 and Cx45 in the entire BB. Cx43 colocalized with Cx40 and Cx45 only in the very distal BB. Subcellular distribution of gap junctions differed between proximal and distal BBs. Geometry of the midseptal and distal BBs revealed on both sides a profuse network of interlacing fibers, whereas the proximal BB consisted of a single (right BB) or multiple (left BB) parallel fibers. CONCLUSIONS: Comparison of connexin expression/distribution, geometry of the BBs, and CV characteristics suggests that increased path length for activation resulting from BB geometry is responsible for the apparently reduced CV in the midseptal BB of the mouse heart.

Animals↗

PubMed2004

Architectural and functional asymmetry of the His-Purkinje system of the murine heart.

OBJECTIVE: The aim of this work was to target a vital reporter gene in the mouse cardiac conduction system (CS) to distinguish this tissue from the surrounding myocardium in the adult heart. METHODS: A transgenic mouse line has been created in which EGFP is expressed under the control of the Cx40 gene. Correlative investigations associating EGFP imaging and electrophysiological techniques were carried out on the adult heart and isolated cardiomyocytes. RESULTS: In the heart of the Cx40(EGFP/+) mice, EGFP signal was seen in the coronary arteries, the atria, the atrioventricular (AV) node and the His-Purkinje system. The latter was found to be structurally and functionally asymmetrical. The anatomical asymmetry was apparent in both the number of strands or fasciculi making up the His bundle branches (BBs) (1 strand on the right, 20 or so on the left), and the density (low on the right, high on the left) of the network of Purkinje fibers (PFs) that extends over the ventricular wall surfaces. The profiles of the electrical activation patterns recorded on the right and left flanks of the septum were also asymmetrical, mirroring the architecture of the branches. EGFP made it easy to identify the Purkinje cells in populations of dissociated cardiomyocytes and they were investigated using the patch-clamp technique. The hyperpolarization-activated current (If) was recorded in all spontaneously active Purkinje cells. CONCLUSIONS: This investigation provides positive evidence of the asymmetry of the His-Purkinje system of the adult mouse, and the first patch-clamp recording data on murine cardiac Purkinje cells. This mouse model opens up new perspectives for investigating the contribution of specific genes to the morphology and function of the His-Purkinje system.

Action Potentials↗

PubMed2004

Genetically modified mice: tools to decode the functions of connexins in the heart-new models for cardiovascular research.

It has long been known that gap junctions are required for the propagation of electrical impulse in the heart. A good deal later, the connexins (Cxs), which are probably exclusive components of the junctional channels that constitute the gap junctions, were identified. More recently, the in vivo functions of cardiac Cxs have been investigated by the analysis of genetically modified mice. These studies have confirmed that Cxs are involved in cardiac impulse conduction, and, unexpectedly, in heart morphogenesis. In addition, cardiac abnormalities described in mice genetically modified for Cx genes, and those observed in certain human cardiac diseases, have been proven to be similar.

Animals↗

PubMed2004

SCL interacts with VEGF to suppress apoptosis at the onset of hematopoiesis.

During development, hematopoiesis initiates in the yolk sac through a process that depends on VEGF/Flk1 signaling and on the function of the SCL/Tal1 transcription factor. Here we show that VEGF modifies the developmental potential of primitive erythroid progenitors and prolongs their life span. Furthermore, the survival of yolk sac erythrocytes in vivo depends on the dose of VEGF. Interestingly, in Vegf(lo/lo) embryos carrying a hypomorph allele, Flk1-positive cells reach the yolk sac at E8.5, but are severely compromised in their ability to generate primitive erythroid precursors. These observations indicate that during embryonic development, different thresholds of VEGF are required for the migration and clonal expansion of hematopoietic precursors. The near absence of primitive erythroid precursors in Vegf(lo/lo) embryos correlates with low levels of Scl in the yolk sac. Strikingly, gain-of-function of SCL partially complements the hematopoietic defect caused by the hypomorph Vegf(lo) allele, and re-establishes the survival of erythroid cells and the expression of erythroid genes (Gata1 and betaH1). This indicates that SCL functions downstream of VEGF to ensure an expansion of the hematopoietic compartment.

Animals↗

PubMed2003

Cortical and retinal defects caused by dosage-dependent reductions in VEGF-A paracrine signaling.

To determine the function of VEGF-A in nervous system development, we have utilized the Nestin promoter-driven Cre recombinase transgene, in conjunction with a conditional and hypomorphic VEGF-A allele, to lower VEGF-A activity in neural progenitor cells. Mice with intermediate levels of VEGF-A activity showed decreased blood vessel branching and density in the cortex and retina, resulting in a thinner retina and aberrant structural organization of the cortex. Severe reductions in VEGF-A led to decreases in vascularity and subsequent hypoxia, resulting in the specific degeneration of the cerebral cortex and neonatal lethality. Decreased neuronal proliferation and hypoxia was evident at E11.5, leading to increased neuronal apoptosis in the cortex by E15.5. In order to address whether the observed changes in the structural organization of the nervous system were due to a direct and autocrine role of VEGF-A on the neural population, we conditionally inactivated the main VEGF-A receptor, Flk1, specifically in neuronal lineages, by using the Nestin Cre transgene. The normality of these mice ruled out the possibility that VEGF-A/Flk1 signaling has a significant autocrine role in CNS development. VEGF-A dosage is therefore a critical parameter regulating the density of the vascular plexus in the developing CNS that is in turn a key determinant in the development and architectural organization of the nervous system.

Animals↗

PubMed2003

Contrasting effects of VEGF gene disruption in embryonic stem cell-derived versus oncogene-induced tumors.

Previous gene targeting studies have implicated an indispensable role of vascular endothelial growth factor (VEGF) in tumor angiogenesis, particularly in tumors of embryonal or endocrine origin. In contrast, we report here that transformation of VEGF-deficient adult fibroblasts (MDF528) with ras or neu oncogenes gives rise to highly tumorigenic and angiogenic fibrosarcomas. These aggressive VEGF-null tumors (528ras, 528neu) originated from VEGF(-/-) embryonic stem cells, which themselves were tumorigenically deficient. We also report that VEGF production by tumor stroma has a modest role in oncogene-driven tumor angiogenesis. Both ras and neu oncogenes down-regulated at least two endogenous inhibitors of angiogenesis [pigment epithelium derived factor (PEDF) and thrombospondin 1 (TSP-1)]. This is functionally important as administration of an antiangiogenic TSP-1 peptide (ABT-526) markedly inhibited growth of VEGF(-/-) tumors, with some ingress of pericytes. These results provide the first definitive genetic demonstration of the dispensability of tumor cell-derived VEGF in certain cases of 'adult' tumor angiogenesis, and thus highlight the importance of considering VEGF-independent as well as VEGF-dependent pathways when attempting to block this process pharmacologically.

Angiogenesis Inducing Agents↗

PubMed2002

Early steps of a thymic tumor in SV40 transgenic mice: hyperplasia of medullary epithelial cells and increased mature thymocyte numbers disturb thymic export.

Bone marrow progenitors migrate to the thymus, where they proliferate and differentiate into immunologically competent T cells. In this report we show that mice transgenic for SV40 T and t antigens under the control of the L-pyruvate kinase promoter develop, in a first step, thymic hyperplasia of both thymocytes and epithelial cells. Morphological studies (histology, immunohistolabeling and electron microscopy) revealed modifications of the thymic microenvironment and gradual expansion of medullary epithelial cells in 1 month-old mice, taking over the cortical region. Then, a thymic carcinoma develops. Two-color labeling of frozen sections identified the transgene in medullary epithelial cells. Flow cytometry analysis demonstrated a marked increase in mature CD4+ and CD8+ thymocytes in adult mice (39 +/- 10 x 10(6) in transgenic mice and 12 +/- 5 x 10(6) in age-matched controls). Furthermore, thymocyte export was disturbed.

Animals↗

PubMed2002

Insufficient VEGFA activity in yolk sac endoderm compromises haematopoietic and endothelial differentiation.

Vascular endothelial growth factor A (VEGFA) plays a pivotal role in the first steps of endothelial and haematopoietic development in the yolk sac, as well as in the establishment of the cardiovascular system of the embryo. At the onset of gastrulation, VEGFA is primarily expressed in the yolk sac visceral endoderm and in the yolk sac mesothelium. We report the generation and analysis of a Vegf hypomorphic allele, Vegf(lo). Animals heterozygous for the targeted mutation are viable. Homozygous embryos, however, die at 9.0 dpc because of severe abnormalities in the yolk sac vasculature and deficiencies in the development of the dorsal aortae. We find that providing 'Vegf wild-type' visceral endoderm to the hypomorphic embryos restores normal blood and endothelial differentiation in the yolk sac, but does not rescue the phenotype in the embryo proper. In the opposite situation, however, when Vegf hypomorphic visceral endoderm is provided to a wild-type embryo, the 'Vegf wild-type' yolk sac mesoderm is not sufficient to support proper vessel formation and haematopoietic differentiation in this extra-embryonic membrane. These findings demonstrate that VEGFA expression in the visceral endoderm is absolutely required for the normal expansion and organisation of both the endothelial and haematopoietic lineages in the early sites of vessel and blood formation. However, normal VEGFA expression in the yolk sac mesoderm alone is not sufficient for supporting the proper development of the early vascular and haematopoietic system.

3' Untranslated Regions↗