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M J Scott

Publications and source records attributed to M J Scott.

At least 37 records · Page 2Linked to original sources
PubMed2000

A repressible female-specific lethal genetic system for making transgenic insect strains suitable for a sterile-release program.

We have developed a tetracycline-repressible female-specific lethal genetic system in the vinegar fly Drosophila melanogaster. One component of the system is the tetracycline-controlled transactivator gene under the control of the fat body and female-specific transcription enhancer from the yolk protein 1 gene. The other component consists of the proapoptotic gene hid under the control of a tetracycline-responsive element. Males and females of a strain carrying both components are viable on medium supplemented with tetracycline, but only males survive on normal medium. A strain with such properties would be ideal for a sterile-insect release program, which is most effective when only males are released in the field.

Animals↗
PubMed2000

Alkali salts of C3-symmetric, linked aryloxides: selective binding of substrates with metal aggregates.

The lithium, sodium, and potassium salts of tris(3,5-dialkyl-2-hydroxyphenyl)methanes (tert-butyl, tert-pentyl, methyl) have been prepared by reaction of the triarylmethane with n-butyllithium, sodium hydride, and potassium hydride, respectively. These compounds are all hexanuclear aggregates composed of two triarylmethane units. Whereas the lithium salt is compact and cannot bind oxygen-donor solvent molecules, the sodium and potassium systems have vacant coordination sites that can interact with solvents. For the sodium compounds, the solvent can be subsequently removed, and the resulting coordinatively unsaturated compounds have been shown to selectively bind oxygen-donor substrates (ethers, aldehydes, and ketones) of suitable size and shape. The paper reports the synthesis and characterization of these novel compounds, including thirteen crystal structures of the salts and their adducts.

Journal Article↗
PubMed2000

Effect of grafted polyethylene glycol (PEG) on the size, encapsulation efficiency and permeability of vesicles.

Liposomes have been prepared by the vesicle extrusion method (VETs) from mixtures of dipalmitoylphosphatidylcholine (DPPC), phosphatidylinositol (PI) and dipalmitoylphosphatidylethanolamine with covalently linked poly(ethylene glycol) molecular mass 5000 and 2000 (DPPE-PEG 5000 and DPPE-PEG 2000) covering a range of 0-7.5 mole%. The encapsulation of D-glucose has been studied and found to be markedly dependent on the mole% DPPE-PEG. The permeability of the liposomes to D-glucose has been measured both as a function of temperature and liposome composition. The permeability coefficients for D-glucose increase with mole% DPPE-PEG 5000 and with temperature over the range 25-50 degrees C. The activation energies for glucose permeability range from 90 to 23 kJ mol(-1). The decrease in activation energy with increasing temperature is attributed to an increasing number of bilayer defects as the liposome content of PEG-grafted lipid is increased. The dependence of D-glucose encapsulation as a function of PEG-grafted lipid content is discussed in terms of the conformation of the PEG molecules on the inner surface of the bilayer. For liposomes containing DPPE-PEG 5000 the relative percentage encapsulation of glucose, assuming that the PEG surface layer excludes glucose, is comparable to that predicted from the mushroom and brush conformational models.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2000

MSL1 plays a central role in assembly of the MSL complex, essential for dosage compensation in Drosophila.

In male Drosophila, histone H4 acetylated at Lys16 is enriched on the X chromosome, and most X-linked genes are transcribed at a higher rate than in females (thus achieving dosage compensation). Five proteins, collectively called the MSLs, are required for dosage compensation and male viability. Here we show that one of these proteins, MSL1, interacts with three others, MSL2, MSL3 and MOF. The latter is a putative histone acetyl transferase. Overexpression of either the N- or C-terminal domain of MSL1 has dominant-negative effects, i.e. causes male-specific lethality. The lethality due to expression of the N-terminal domain is reduced if msl2 is co-overexpressed. MSL2 co-purifies over a FLAG affinity column with the tagged region of MSL1, and both MSL3 and MOF co-purify with the FLAG-tagged MSL1 C-terminal domain. Furthermore, the MSL1 C-terminal domain binds specifically to a GST-MOF fusion protein and co-immunoprecipitates with HA-tagged MSL3. The MSL1 C-terminal domain shows similarity to a region of mouse CBP, a transcription co-activator. We conclude that a main role of MSL1 is to serve as the backbone for assembly of the MSL complex.

Amino Acid Sequence↗
PubMed2000

High-resolution MRI characterization of human thrombus using a novel fibrin-targeted paramagnetic nanoparticle contrast agent.

In this study, the sensitivity of a novel fibrin-targeted contrast agent for fibrin detection was defined in vitro on human thrombus. The contrast agent was a lipid-encapsulated perfluorocarbon nanoparticle with numerous Gd-DTPA complexes incorporated into the outer surface. After binding to fibrin clots, scanning electron microscopy of treated clots revealed dense accumulation of nanoparticles on the clot surfaces. Fibrin clots with sizes ranging from 0.5-7.0 mm were imaged at 4.7 T with or without treatment with the targeted contrast agent. Regardless of sizes, untreated clots were not detectable by T(1)-weighted MRI, while targeted contrast agent dramatically improved the detectability of all clots. Decreases in T(1) and T(2) relaxation times (20-40%) were measured relative to the surrounding media and the control clots. These results suggest the potential for sensitive and specific detection of microthrombi that form on the intimal surfaces of unstable atherosclerotic plaque.

Antibodies, Monoclonal↗
PubMed2000

High-frequency ultrasound for quantitative characterization of myocardial edema.

Myocardial edema has been associated with impaired ventricular compliance and diastolic filling. To determine the sensitivity of high-frequency (40 MHz) ultrasound to myocardial edema, we employed a model in which myocardial edema was induced by immersion of tissue in isotonic saline. The effect of freezing tissue on edema formation was also evaluated. Rat hearts were arrested at end-diastole and insonified fresh within 15 min of excision (n = 5) or following being frozen for 24 h and thawed (n = 4). Measurements of attenuation, backscatter, tissue thickness and speed of sound were performed at baseline and hourly for 4 h, and compared with direct measurements of myocardial edema. Fresh tissue demonstrated a greater propensity for the development of edema than frozen tissue. Integrated backscatter increased in both tissues, whereas the magnitude and slope of attenuation decreased as edema evolved. We conclude that high-frequency ultrasound sensitively detects myocardial edema, and we propose that the extension of these methods to clinical frequencies may prove useful for monitoring and treatment of cardiac edematous disease states.

Acoustics↗
PubMed2000

Delineation of the extracellular determinants of ultrasonic scattering from elastic arteries.

Elastic arteries consist of three primary components: elastin fibers, extracellular collagen matrix and smooth muscle cells. However, the relative contribution of elastin and collagen fibers to overall ultrasonic scattering from an intact arterial wall is poorly understood. To define the principal source of extracellular scattering from the medial layer of elastic arteries, canine ascending aortas (n = 10) were excised, fixed and sectioned for insonification. Subsequently, aortic specimens were restudied after treatment to dissolve all tissue components except extracellular collagen matrix (n = 5) and elastin fibers (n = 5). Histological staining revealed very few elastin fibers and sparse intact collagen in collagen-isolated and elastin-isolated tissues, respectively. Integrated backscatter, attenuation and backscatter coefficients differentiated these two treated tissues. The backscatter coefficient for elastin-isolated tissue demonstrated a fivefold increase over collagen-isolated tissue, suggesting that elastin fibers represent a primary scattering component within elastic arteries, and the collagen fibers may provide a secondary component of scattering.

Animals↗
PubMed2000

In vivo molecular imaging of stretch-induced tissue factor in carotid arteries with ligand-targeted nanoparticles.

Molecular imaging permits tissues to be functionally characterized by identification of specific cell-surface receptors with targeted contrast agents. In our study, a ligand-targeted acoustic nanoparticle system was used to identify the angioplasty-induced expression of tissue factor by smooth muscle cells within the tunica media. Pig carotid arteries were overstretched bilaterally with balloon catheters, treated with a tissue factor-targeted or a control nanoparticle system, and imaged with intravascular ultrasound (20 MHz) before and after treatment. Carotid wall acoustic reflectivities were unaffected by overstretch injury. Tissue factor-targeted nanoemulsion bound and increased the echogenicity of smooth muscle cells expressing tissue factor within the tunica media. The targeted emulsion increased the arterial wall gray scale (99.4+/-14.5; P<.05) relative to pretreatment (41.8+/-11.1, P<0.05) and the control gray scale (pre-emulsion: 49.3+/-9.5; post-emulsion: 43.7+/-6.4; P<.05). The area of acoustic enhancement appeared to coincide with expression of induced tissue factor in the tunica media confirmed by immunohistochemistry. We have demonstrated that this novel nanoemulsion can infiltrate into arterial walls after balloon injury and localize the expression of overstretch-induced tissue factor within pig carotid arteries. Molecular imaging and quantification of complex, biochemical change, such as tissue factor expression after angioplasty, may prove to be a prognostically important predictor of subsequent restenosis.

Acoustics↗
PubMed2000

Molecular imaging of stretch-induced tissue factor expression in carotid arteries with intravascular ultrasound.

RATIONALE AND OBJECTIVES: Molecular imaging with targeted contrast agents enables tissues to be distinguished by detecting specific cell-surface receptors. In the present study, a ligand-targeted acoustic nanoparticle system is used to identify angioplasty-induced expression of tissue factor by smooth muscle cells within carotid arteries. METHODS: Pig carotid arteries were overstretched with balloon catheters, treated with tissue factor-targeted or a control nanoparticle system, and imaged with intravascular ultrasound before and after treatment. RESULTS: Tissue factor-targeted emulsions bound and increased the echogenicity and gray-scale levels of overstretched smooth muscle cells within the tunica media, versus no change in contralateral control arteries. Expression of stretch-induced tissue factor in carotid artery media was confirmed by immunohistochemistry. CONCLUSIONS: The potential for abnormal thrombogenicity of balloon-injured arteries, as reflected by smooth muscle expression of tissue factor, was imaged using a novel, targeted, nanoparticulate ultrasonic contrast agent.

Animals↗
PubMed2000

Time evolution of enhanced ultrasonic reflection using a fibrin-targeted nanoparticulate contrast agent.

Complex molecular signaling heralds the early stages of pathologies such as angiogenesis, inflammation, unstable atherosclerotic plaques, and areas of remote thrombi. In previous studies, acoustic enhancement of blood clot morphology was demonstrated with the use of a nongaseous, fibrin-targeted acoustic nanoparticle emulsion delivered to areas of thrombosis both in vitro and in vivo. In this study, a system was designed and constructed that allows visualization of the evolution of acoustic contrast enhancement. To evaluate the system, two targets were examined: avidin-complexed nitrocellulose membrane and human plasma clots. The time evolution of enhancement was visualized in 10-min increments for 1 h. A monotonic increase was observed in ultrasonic reflection enhancement from specially treated nitrocellulose membranes for targeted emulsions containing perfluorooctylbromide (1.30+/-0.3 dB) and for perfluorooctane (2.64+/-0.5 dB) within the first 60 min of imaging. In comparison, the inherently nonechogenic plasma clots showed a substantial increase of 12.0+/-0.9 dB when targeted with a perfluoro-octane emulsion. This study demonstrates the concept of molecular imaging and provides the first quantifiable time-evolution report of the binding of a site-targeted ultrasonic contrast agent. Moreover, with the incorporation of specific drug treatments into the nanoparticulate contrast agent, ultrasonic molecular imaging may yield reliable detection and quantification of nascent pathologies and facilitate targeted drug therapy.

Contrast Media↗
PubMed2000

The extracellular matrix is an important source of ultrasound backscatter from myocardium.

Ultrasound tissue characterization with measurement of backscatter has been employed in numerous experimental and clinical studies of cardiac pathology, yet the cellular components responsible for scattering from cardiac tissues have not been unequivocally identified. This laboratory has proposed a mathematical model for myocardial backscatter that postulates the fibrous extracellular matrix (ECM) as a significant determinant of backscatter. To demonstrate the importance of ECM, this group sought to determine whether measurements of backscatter from the isolated ECM could reproduce the known directional dependence, or anisotropy of backscatter, from intact cardiac tissues in vitro. Segments of left ventricular free wall from ten formalin fixed porcine hearts were insonified at 50 MHz, traversing the heart wall from endo- to epicardium to measure the anisotropy of myocardial backscatter, defined as the difference between peak (perpendicular to fibers) and trough (parallel to fibers) backscatter amplitude. The tissue segments were then treated with 10% NaOH to dissolve all of the cellular components, leaving only the intact ECM. Scanning electron micrographs (SEM) were obtained of tissue sections to reveal complete digestion of the cellular elements. The dimensions of the residual voids resulting from cell digestion were approximately the diameter of the intact myocytes (10-30 microm). These samples were reinsonified after seven days of treatment to compare the anisotropy of integrated backscatter. The magnitude of anisotropy of backscatter changed from 15.4 +/- 0.8 to 12.6 +/- 1.1dB for intact as compared with digested specimens. Because digestion of the myocardium leaves only extracellular sources of ultrasonic scattering, and because the isolated ECM exhibits similar ultrasonic anisotropy as does the intact myocardium, it is concluded that there is a direct association between the ECM and the anisotropy of backscatter within intact tissue. Thus, it is suggested that ultrasonic tissue characterization represents a potentially clinically applicable method for delineating the structure and function of the ECM.

Animals↗
PubMed1999

Development of an insulated reporter system to search for cis-acting DNA sequences required for dosage compensation in Drosophila.

Dosage compensation (equalization of X-linked gene products) occurs in Drosophila melanogaster by a two-fold transcriptional increase of X-linked gene expression in the male. The cis-acting X-linked DNA sequences required for dosage compensation (called DCREs) remain elusive, despite numerous attempts to identify them. We have developed an insulated reporter system to minimise problems previously encountered with identifying these elements. The system consists of the constitutive autosomal armadillo promoter fused to the lacZ reporter gene (called arm-lacZ) which was flanked by SCS insulator elements to block potential repressive effects of an autosomal chromatin environment. Seven X-linked DNA fragments, totaling 62.7 kb, were each inserted between the SCS element and the armadillo promoter. If an X-linked fragment contains a DCRE, then transgenic males carrying an autosomal insert of the construct should produce twice the beta-galactosidase activity of females. However, in all cases, males and females expressed the same level of lacZ. Thus, it's likely that none of the X-linked fragments contained a DCRE, suggesting these elements may be rarer than previously thought. The insulated reporter system was also used to test the hypothesis that some genes may be dosage compensated due to repression by Sex lethal (Sxl) in females. A fragment from the runt gene containing three Sxl binding sites was inserted into the 3' untranslated region of arm-lacZ. Transgenic males carrying an autosomal insert of the construct had on average 1.31-1.46 times the level of beta-galactosidase than females, suggesting that some genes could be compensated, at least partially, by Sxl repression in females.

Animals↗
PubMed1998

The carriage of Pasteurella haemolytica in sheep and its transfer between ewes and lambs in relation to mastitis.

The possible presence of Pasteurella haemolytica in the mouth of lambs and on the skin of the teats of ewes was investigated. The organism was found in the mouth of ewes and lambs and, soon after lambing, on the teat skin of ewes. It was not isolated from the teat skin of pregnant ewes 1-14 days before lambing or from the teat skin one week after the lambs had been weaned. The transfer of P. haemolytica to the teat skin is undoubtedly mediated by the lamb. There is ample opportunity for the teat orifice to be exposed to P. haemolytica during the suckling period and it is known that only a few colony-forming units of virulent organisms are required to initiate mastitis.

Animals↗
PubMed1998

In vitro characterization of a novel, tissue-targeted ultrasonic contrast system with acoustic microscopy.

Targeted ultrasonic contrast systems are designed to enhance the reflectivity of selected tissues in vivo [Lanza et al., Circulation 94, 3334 (1996)]. In particular, these agents hold promise for the minimally invasive diagnosis and treatment of a wide array of pathologies, most notably tumors, thromboses, and inflamed tissues. In the present study, acoustic microscopy was used to assess the efficacy of a novel, perfluorocarbon based contrast agent to enhance the inherent acoustic reflectivity of biological and synthetic substrates. Data from these experiments were used to postulate a simple model describing the observed enhancements. Frequency averaged reflectivity (30-55 MHz) was shown to increase 7.0 +/- 1.1 dB for nitrocellulose membranes with targeted contrast. Enhancements of 36.0 +/- 2.3 dB and 8.5 +/- 0.9 dB for plasma and whole blood clots, respectively, were measured between 20 and 35 MHz. A proposed acoustic transmission line model predicted the targeted contrast system would increase the acoustic reflectivity of the nitrocellulose membrane, whole blood clot, and fibrin plasma clot by 2.6, 8.0, and 31.8 dB, respectively. These predictions were in reasonable agreement with the experimental results of this paper. In conclusion, acoustic microscopy provides a rapid and sensitive approach for in vitro chracterization, development, and testing of mathematical models of targeted contrast systems. Given the current demand for targeted contrast systems for medical diagnostic and therapeutic use, the use of acoustic microscopy may provide a useful tool in the development of these agents.

Acoustics↗
PubMed1997

High-frequency ultrasonic detection of thrombi with a targeted contrast system.

Site-targeted acoustic contrast agents used in conjunction with high-frequency intravascular ultrasound have the potential to localize and characterize intravascular pathology. The present study quantifies the utility of a novel, site-targeted ultrasonic contrast agent with high-frequency ultrasound (30 to 50 MHz) and demonstrates the feasibility of the new agent for augmenting detection of targeted pathology with intravascular ultrasonic catheters. High-frequency acoustic microscopy was used to image avidinconjugated nitrocellulose membranes after exposure to a control or biotinylated contrast agent. Increases (p < 0.05) in backscattered power of approximately 66 dB (4-fold) were found for the biotinylated, but not the control contrast agent. Intravascular ultrasonic images (30 MHz nominal center frequency) of plasma clots after exposure to the targeted contrast agent were brighter (p < 0.05) than in controls. These results demonstrate high-frequency acoustic enhancement with a novel targeted contrast agent and may extend the potential diagnostic spectrum of intravascular ultrasound.

Avidin↗