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J F Martin

Publications and source records attributed to J F Martin.

At least 127 records · Page 7Linked to original sources
PubMed1994

A Mef2 gene that generates a muscle-specific isoform via alternative mRNA splicing.

Members of the myocyte-specific enhancer-binding factor 2 (MEF2) family of transcription factors bind a conserved A/T-rich sequence in the control regions of numerous muscle-specific genes. Mammalian MEF2 proteins have been shown previously to be encoded by three genes, Mef2, xMef2, and Mef2c, each of which gives rise to multiple alternatively spliced transcripts. We describe the cloning of a new member of the MEF2 family from mice, termed MEF2D, which shares extensive homology with other MEF2 proteins but is the product of a separate gene. MEF2D binds to and activates transcription through the MEF2 site and forms heterodimers with other members of the MEF2 family. Deletion mutations show that the carboxyl terminus of MEF2D is required for efficient transactivation. MEF2D transcripts are widely expressed, but alternative splicing of MEF2D transcripts gives rise to a muscle-specific isoform which is induced during myoblast differentiation. The mouse Mef2, Mef2c, and Mef2d genes map to chromosomes 7, 13, and 3, respectively. The complexity of the MEF2 family of regulatory proteins provides the potential for fine-tuning of transcriptional responses as a consequence of combinatorial interactions among multiple MEF2 isoforms encoded by the four Mef2 genes.

Alternative Splicing↗
PubMed1994

A novel myogenic regulatory circuit controls slow/cardiac troponin C gene transcription in skeletal muscle.

The slow/cardiac troponin C (cTnC) gene is expressed in three distinct striated muscle lineages: cardiac myocytes, embryonic fast skeletal myotubes, and adult slow skeletal myocytes. We have reported previously that cTnC gene expression in cardiac muscle is regulated by a cardiac-specific promoter/enhancer located in the 5' flanking region of the gene (bp -124 to +1). In this report, we demonstrate that the cTnC gene contains a second distinct and independent transcriptional enhancer which is located in the first intron. This second enhancer is skeletal myotube specific and is developmentally up-regulated during the differentiation of myoblasts to myotubes. This enhancer contains three functionally important nuclear protein binding sites: a CACCC box, a MEF-2 binding site, and a previously undescribed nuclear protein binding site, designated MEF-3, which is also present in a large number of skeletal muscle-specific transcriptional enhancers. Unlike most skeletal muscle-specific transcriptional regulatory elements, the cTnC enhancer does not contain a consensus binding site (CANNTG) for the basic helix-loop-helix (bHLH) family of transcription factors and does not directly bind MyoD-E12 protein complexes. Despite these findings, the cTnC enhancer can be transactivated by overexpression of the myogenic bHLH proteins, MyoD and myogenin, in C3H10T1/2 (10T1/2) cells. Electrophoretic mobility shift assays demonstrated changes in the patterns of MEF-2, CACCC, and MEF-3 DNA binding activities following the conversion of 10T1/2 cells into myoblasts and myotubes by stable transfection with a MyoD expression vector. In particular, MEF-2 binding activity was up-regulated in 10T1/2 cells stably transfected with a MyoD expression vector only after these cells fused and differentiated into skeletal myotubes. Taken together, these results demonstrated that distinct lineage-specific transcriptional regulatory elements control the expression of a single myofibrillar protein gene in fast skeletal and cardiac muscle. In addition, they show that bHLH transcription factors can indirectly transactivate the expression of some muscle-specific genes.

Amino Acid Sequence↗
PubMed1994

Mef2 gene expression marks the cardiac and skeletal muscle lineages during mouse embryogenesis.

Members of the MEF2 family of transcription factors bind a conserved A/T-rich sequence in the control regions of many skeletal and cardiac muscle genes. To begin to assess the roles of the different Mef2 genes in the control of muscle gene expression in vivo, we analyzed by in situ hybridization the expression patterns of the Mef2a, Mef2c and Mef2d genes during mouse embryogenesis. We first detected MEF2C expression at day 7.5 postcoitum (p.c.) in cells of the cardiac mesoderm that give rise to the primitive heart tube, making MEF2C one of the earliest markers for the cardiac muscle lineage yet described. By day 8.5, MEF2A, MEF2C and MEF2D mRNAs are all detected in the myocardium. By day 9.0, MEF2C is expressed in rostral myotomes, where its expression lags by about a day behind that of myf5 and several hours behind that of myogenin. MEF2A and MEF2D are expressed at a lower level than MEF2C in the myotome at day 9.5 and are detected in more embryonic tissues than MEF2C. Expression of each of the MEF2 transcripts is observed in muscle-forming regions within the limbs at day 11.5 p.c. and within muscle fibers throughout the embryo at later developmental stages. The expression of MEF2C in the somites and fetal muscle is distinct from that of MEF2A, MEF2D and the myogenic bHLH regulatory genes, suggesting that it may represent a distinct myogenic cell type. Neural crest cells also express high levels of MEF2 mRNAs between days 8.5 and 10.5 of gestation. After day 12.5 p.c., MEF2 transcripts are detected at high levels in specific regions of the brain and ultimately in a wide range of tissues. The distinct patterns of expression of the different Mef2 genes during mouse embryogenesis suggest that these genes respond to unique developmental cues and support the notion that their products play roles in the regulation of muscle-specific transcription during establishment of the cardiac and skeletal muscle lineages.

Animals↗
PubMed1993

Myocyte enhancer factor (MEF) 2C: a tissue-restricted member of the MEF-2 family of transcription factors.

MEF-2 is a muscle-specific DNA binding activity that recognizes an A+T-rich sequence found in the control regions of numerous muscle-specific genes. The recent cloning of MEF-2 showed that it belongs to the MADS (MCM1, Agamous, Deficiens, and serum-response factor) box family of transcription factors and that MEF-2 mRNA is expressed ubiquitously. Here we describe the cloning of a member of the MEF-2 gene family, referred to as MEF-2C, that is nearly identical to other MEF-2 gene products in the MADS box but diverges from other members of the family outside of this domain. MEF-2C binds the MEF-2 site with high affinity and can activate transcription of a reporter gene linked to tandem copies of that site. In contrast to previously described members of the MEF-2 family, MEF-2C transcripts are highly enriched in skeletal muscle, spleen, and brain of adult mice and are upregulated during myoblast differentiation. These results suggest that the MEF-2 site is a target for a diverse family of proteins that regulates transcription in a variety of cell types.

Amino Acid Sequence↗
PubMed1993

Nitric oxide synthase activities in human myocardium.

Myocardial constitutive and inducible nitric oxide (NO) synthase activities were measured in right ventricular tissue from 17 patients with dilated cardiomyopathy (DCM). A significant activity of inducible enzyme was accompanied by a low activity of the constitutive NO synthase. Thus, the myocardium has the capacity to express both NO synthases. NO may have a physiological as well as a pathological role in the human myocardium.

Amino Acid Oxidoreductases↗
PubMed1993

[125I]-endothelin-1 binding to vasa vasorum and regions of neovascularization in human and porcine blood vessels: a possible role for endothelin in intimal hyperplasia and atherosclerosis.

The distribution of [125I]-endothelin-1 (ET-1) binding sites on human and porcine vessels was studied with in vitro receptor autoradiography. Binding to normal human saphenous veins was compared to atheromatous veins used as coronary artery bypass grafts. Binding to porcine vessels, from an experimental model of intimal hyperplasia, was also studied. There was dense binding of [125I]-ET-1 to smooth muscle of all vessels examined, as well as to the vasa vasorum and regions of neovascularization of diseased vessels. Binding to microvasculature (vasa vasorum and regions of neovascularization) is of particular interest, because ET-1 has been shown to have mitogenic activity on vascular smooth-muscle cells in culture and microvessels are extremely sensitive to the constrictor effect of ET-1. Binding of [125I]-ET-1 to vasa vasorum of normal blood vessels and to regions of neovascularization of atheromatous vessels suggests that ET-1 plays a pathophysiologic role in atherosclerosis.

Animals↗
PubMed1993

L-arginine infusion has no effect on systemic haemodynamics in normal volunteers, or systemic and pulmonary haemodynamics in patients with elevated pulmonary vascular resistance.

1. The evidence that the infusion of L-arginine, the precursor of endothelium-derived relaxing factor (EDRF)/nitric oxide (NO), may reduce systemic blood pressure, via the generation of intracellular cyclic guanosine-3,5-monophosphate(cGMP), in normotensive volunteers is controversial. In the first part of the study we investigated the effect of an L-arginine infusion on systemic blood pressure and plasma cGMP in healthy volunteers. 2. Patients with systemic sclerosis have widespread endothelial damage which, by reducing the release of NO, could contribute to the raised pulmonary vascular resistance (PVR) often found in this condition. We hypothesised that if there were a failure of NO synthesis this might be overcome by infusing L-arginine into the pulmonary artery, thereby lowering PVR. In the second part of the study we investigated the effect of L-arginine infusion on systemic and pulmonary haemodynamics, and on plasma cGMP levels in patients with pulmonary hypertension and systemic sclerosis. 3. L-arginine (500 mg kg-1) was infused over 30 min into five normotensive volunteers and five patients with systemic sclerosis and pulmonary hypertension. Blood pressure, heart rate and skin temperature were measured non-invasively in the volunteers and systemic and pulmonary haemodynamics recorded via radial artery cannulae and balloon-tipped, flow directed, pulmonary artery catheters in the patients with systemic sclerosis. 4. L-arginine had no significant effect on blood pressure, heart rate or skin temperature in the normotensive volunteers nor on systemic or pulmonary haemodynamics in the systemic sclerotic group. Cyclic-GMP levels did not significantly change in either group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

The relationship between human megakaryocyte nuclear DNA content and gene expression.

Increased platelet reactivity has been implicated in various vascular diseases. Since the protein content of platelets is determined mainly by the megakaryocyte, alterations in megakaryocyte mRNA expression may influence platelet protein content and therefore activity. In order to determine whether DNA content (ploidy) of a megakaryocyte influences its mRNA expression, we have developed a method to investigate the relationship between megakaryocyte ploidy and gene expression. By measuring the ploidy and mRNA expression in individual cells, we have shown that in the physiological state there is an increase in mRNA expression for beta-actin, glycoprotein IIb and neuropeptide Y with increase in ploidy and that this increase levels off at high ploidy values. This may have relevance in the understanding of platelet reactivity in pathological events.

Actins↗
PubMed1993

The regulation of megakaryocyte polyploidization and its implications for coronary artery occlusion.

Polyploidization is a distinctive feature of megakaryocyte differentiation. The physiological meaning and the regulation of this process are obscure. Megakaryocyte ploidy varies in normal biology and in disease. Here we review the evidence suggesting that ploidy changes may have a role in the determination of platelet reactivity and in the aetiology of coronary artery occlusion. We also present a hypothesis that may serve as a framework to explore the regulation of megakaryocyte polyploidization at the molecular level and also may provide a rational basis to explain the occurrence of ploidy changes in ischaemic heart disease.

Animals↗
PubMed1993

Antimicrotubule agents induce polyploidization of human leukaemic cell lines with megakaryocytic features.

In most eukaryotic cells the regular alternation of chromosome reduplication and cell division is controlled by interdependent relationships which prevent progression to the next cell-cycle phase unless the preceding phase has been completed. Megakaryocytes become polyploid by allowing many rounds of DNA replication without completion of intervening mitoses. To assess the role of cell-cycle dependencies in megakaryocytopoiesis we examined human cell lines which express megakaryocytic features for their ability to continue DNA synthesis and undergo polyploidization in the presence of mitotic poisons. Treatment of HEL cells with colcemid blocked cell division but not cellular DNA synthesis. DNA content distributions of cells treated with colcemid for 48 h showed a marked increase in the proportion of polyploid cells (57.6% +/- 9.9%, n = 16), an increase in cellular size and nuclear lobation. Identical effects were observed in HEL cells treated with colchicine, nocodazole or taxol but not with the inactive compound lumicolchicine. Induction of polyploidization by antimicrotubule agents was also observed in the megakaryoblastic cell lines MEG-01, DAMI and UT-7 but not in the T-cell line MOLT-4 or the promyelocytic cell line HL-60. These results suggest that dependency of DNA replication on completion of the previous mitosis is suppressed in the megakaryocytic lineage.

Cell Division↗
PubMed1993

Influence of platelet size before coronary angioplasty on subsequent restenosis.

Platelet size has been shown to reflect platelet activity. We prospectively measured the mean platelet volume (MPV) in 47 patients undergoing single vessel angioplasty for symptomatic angina. The patients underwent repeat angiography 4-8 months later irrespective of symptomatic status. Restenosis was assessed quantitatively by hand held calliper measurements of the lesion and qualitatively by a return of angina, ST segment changes on an exercise test and visual analysis of the lesion severity by two experienced angiographers. Twenty-four patients developed recurrent angina during the follow-up period, the MPV in the group with chest pain was 8.54 +/- 0.60 fl compared to 8.1 +/- 0.69 fl in the asymptomatic group (P = 0.04). Twenty two patients had significant ST segment changes at exercise. In this group the MPV was 8.6 +/- 0.56 fl compared to 8.0 +/- 0.70 fl for the group with a negative test (P = 0.002). Similarly visually assessed angiographic stenosis showed a significant increase in the restenotic group (8.6 +/- 0.56 vs. 8.0 +/- 0.61 fl, P = 0.001). The relative odds for developing clinically defined restenosis were 10.2 times greater if the pre-procedural MPV lay in the upper compared to the lowest quartile. There was a positive correlation between MPV and change in minimal luminal diameter between post angioplasty and follow-up angiography, assessed quantitatively, r = +0.56, P = 0.016. There was no association between clinical or angiographic definitions of restenosis and haemoglobin, red cell count, mean corpuscular volume, white cell count or platelet count. Platelet size may influence the development of restenosis after successful coronary angioplasty.

Angioplasty, Balloon, Coronary↗
PubMed1993

Arterial intimal hyperplasia after occlusion of the adventitial vasa vasorum in the pig.

Oxygenation of the arterial wall is provided by diffusion of oxygen outward from the main vessel lumen and inward from the adventitial vasa vasorum. In a group of four Yucatan miniature pigs the oxygenation profiles across the superficial femoral arteries were recorded by polarographic oxygen microelectrodes. The profiles obtained suggested a relatively poorly oxygenated media (a trough value of approximately 25% that of the intimal oxygenation) with a progressive rise in oxygenation toward the intimal and adventitial surfaces. In four other survival experiments, occlusion of the adventitial vasa vasorum by flush ligation of the arterial branches that supply them resulted in the production of a focal, intimal hyperplastic lesion that was absent in control vessels (intimal to medial ratios [mean +/- SEM] of 0.053 +/- 0.008, n = 8, p < 0.001 and 0.013 +/- 0.001, n = 8, respectively). By electron microscopy this lesion was seen to be composed mainly of smooth muscle cells. This evidence would support the hypothesis that arterial wall hypoxia may be involved in the initiation of intimal hyperplasia. It is proposed that human atherosclerosis may be initiated by occlusion of the vasa vasorum and concomitant hypoxia.

Animals↗