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Biomedical subjects

Q Ma

Publications and source records attributed to Q Ma.

At least 91 records · Page 5Linked to original sources
PubMed1997

Direct evidence for a soluble methane monooxygenase from type I methanotrophic bacteria: purification and properties of a soluble methane monooxygenase from Methylomonas sp. GYJ3.

The hydroxylase and reductase components of a soluble methane monooxygenase from type I methanotrophs--Methylomonas sp. GYJ3--were purified by a multiple-step LC procedure. The hydroxylase (approximately 240 kDa, determined by an HPLC-size exclusion chromatography method) has three subunits with molecular masses of 56, 43, and 27 kDa, suggesting that the enzyme has an (alphabeta gamma)2 subunit structure. The HPLC method was developed to purify the hydroxylase component, and the purified protein has a specific activity of 541 nmol propene oxide x mg(-1) protein x min(-1), which is two times the specific activity of the protein purified by the two-step LC procedure. The iron content in the hydroxylase purified by the two-step LC procedure is 2.1 mol of Fe per mole of protein, but the iron content in the protein by the HPLC procedure is 3.78 mol of Fe per mole of protein. The diversity of iron contents in this protein is due mainly to the use of different purification methods. The reductase has a molecular mass of 42 kDa. The UV-VIS spectrum of the protein is similar to that of proteins from other methanotrophs, suggesting that the protein contains a FAD cofactor and a [2Fe-2S] center. The partially purified component B stimulated the MMO activity of the hydroxylase and reductase system by 40-fold.

Chromatography, High Pressure Liquid↗
PubMed1997

Deliberate systemic hypotension to facilitate endovascular therapy of cerebral arteriovenous malformations: a computer modeling study.

With the aid of a computer model, this investigation describes the relationship between mean arterial pressure (MAP) reduction and its effect on total arteriovenous malformation (AVM) shunt flow, feeding artery velocities, and cerebral blood flow in hypotensive, structurally normal vascular beds adjacent to the AVM nidus. Simulations were performed for two feeding artery sizes (2 and 4 mm in diameter) and two AVM shunt flows (500 and 1000 ml/minute) with and without the presence of autoregulation in normal brain. Systemic arterial hypotension was simulated in a stepwise fashion by reducing aortic pressure from 100 to 10 mm Hg in 10-mm Hg steps. The percentage of MAP that resulted in a 50% reduction of shunt flow was calculated (%MAP reduction at half-maximal shunt flow). As the MAP decreased, the shunt flow decreased in a nearly linear fashion; the cerebral blood flow remained constant in neighboring brain until the MAP dropped below 60 and 80 mm Hg for the medium and large AVMs, respectively. The %MAP reductions at half-maximal shunt flow for the medium and large AVMs were not significantly different from 50%: 44% and 47%, respectively. Results for 2 and 4 mm AVM feeding artery sizes were similar. The decrease in both total shunt flow and flow velocity in feeding artery pedicles, potentially embolized by glue injection, were nearly linear with the institution of systemic hypotension. The presence or absence of autoregulation in normal brain, or different variations in the simulated angioarchitecture of the AVMs, did not affect this relationship in the model.

Journal Article↗
PubMed1997

Mash1 and neurogenin1 expression patterns define complementary domains of neuroepithelium in the developing CNS and are correlated with regions expressing notch ligands.

Genetic studies in Drosophila and in vertebrates have implicated basic helix-loop-helix (bHLH) genes in neuronal fate determination and cell type specification. We have compared directly the expression of Mash1 and neurogenin1 (ngn1), two bHLH genes that are expressed specifically at early stages of neurogenesis. In the PNS these genes are expressed in complementary autonomic and sensory lineages. In the CNS in situ hybridization to serial sections and double-labeling experiments indicate that Mash1 and ngn1 are expressed in adjacent and nonoverlapping regions of the neuroepithelium that correspond to future functionally distinct areas of the brain. We also showed that in the PNS several other bHLH genes exhibit similar lineal restriction, as do ngn1 and Mash1, suggesting that complementary cascades of bHLH factors are involved in PNS development. Finally, we found that there is a close association between expression of ngn1 and Mash1 and that of two Notch ligands. These observations suggest a basic plan for vertebrate neurogenesis whereby regionalization of the neuroepithelium is followed by activation of a relatively small number of bHLH genes, which are used repeatedly in complementary domains to promote neural determination and differentiation.

Animals↗
PubMed1997

A novel cytoplasmic protein that interacts with the Ah receptor, contains tetratricopeptide repeat motifs, and augments the transcriptional response to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

To identify new proteins involved in dioxin-dependent signal transduction and transcriptional regulation, we used a yeast two-hybrid system to identify proteins that interact with the Ah receptor (AhR). We cloned a mouse cDNA, which encodes a novel approximately 37-kDa protein that binds to AhR; we have designated the protein as Ah receptor-interacting protein (AIP). The amino acid sequence of mouse AIP exhibits homology with members of the FK506-binding protein family. AIP also contains three tetratricopeptide repeat (TPR) motifs; the TPR sequence is present in proteins required for cell cycle control and RNA synthesis and in steroid receptor-binding immunophilins. Coimmunoprecipitation experiments in mouse hepatoma cells reveal that AIP is cytoplasmic and associates with unliganded Ah receptor and with hsp90; 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment disrupts the AhR-AIP-hsp90 interaction. Overexpression of AIP augments the response of the CYP1A1 gene to 2,3,7,8-tetrachlorodibenzo-p-dioxin. Our data suggest that AIP influences ligand receptivity and/or nuclear targeting of AhR.

Adaptor Proteins, Signal Transducing↗
PubMed1997

A theoretical model of cerebral hemodynamics: application to the study of arteriovenous malformations.

A comprehensive computer model of the cerebral circulation, based on both hydrodynamics and electrical network analysis, was used to investigate the influences of arteriovenous malformations (AVM) on regional cerebral hemodynamics. The basic model contained 114 normal compartments: 55 arteries, 37 veins, 20 microvessel groups (MVG), one compartment representing systemic and extracranial vascular resistance, and one representing the heart. Each microvessel group, which represented the arteriolar bed, consisted of 5000 microvessels. Cerebral blood flow autoregulation was simulated by a formula that determined the resistance and therefore the flow rate of the microvessel groups (arterioles) as a function of perfusion pressure. Elasticity was introduced to describe the compliance of each vessel. Flow rate was made a controlling factor for the positive regulation of the diameters of conductance vessels by calculation of shear stress on the vessel wall (vessel dilation). Models containing an AVM were constructed by adding an AVM compartment and its feeding arteries and draining veins. In addition to the basic model, AVM models were simulated with and without autoregulation and flow-induced conductance vessel dilation to evaluate the contributions of these factors on cerebral hemodynamics. Results for the model with vessel dilation were more similar to clinical observations than those without vessel dilation. Even in the presence of total vasoparalysis of the arteriolar bed equivalent, obliteration of a large (1000 mL/min) shunt flow AVM resulted in a near-field CBF increase from a baseline of 21 to a post-occlusion value of no more than 74 mL/100 g/min, casting doubt on a purely hemodynamic basis for severe hyperemia after treatment. The results of the simulations suggest that our model may be a useful tool to study hemodynamic problems of the cerebral circulation.

Animals↗
PubMed1997

Cerebral arteriovenous malformation feeding artery aneurysms: a theoretical model of intravascular pressure changes after treatment.

OBJECTIVE: A quantitative model may be used to estimate the magnitude of expected pressure changes along the vascular tree with shunt ablation and may provide information to assess the hemodynamic risk of arteriovenous malformation (AVM) treatment. METHODS: A computer model of the cerebral circulation was applied to estimate the changes in intravascular pressure, velocity, biomechanical stress, and shear stress that might be expected from either endovascular or surgical ablation of AVMs. Two AVM sizes and two feeding artery constellations were simulated. The effect of different shunt flows on vascular pressure was modeled. In each simulation, AVMs were occluded in a stepwise fashion. The effects of systemic hypertension and hypotension in various vascular zones were also simulated. RESULTS: As large (1000 ml/min) AVMs were occluded, the mean feeding arterial pressure increased from 18 to 68 mm Hg; the percent-occlusion at half-maximal pressure increase was 92%. For medium (500 ml/min) AVMs, feeding arterial pressure increased from 37 to 66 mm Hg; the percent-occlusion at half-maximal pressure increase was 71%. During manipulation of systemic pressure, hemodynamic changes in the circulation close to the nidus were proportionally less than changes in systemic pressure; the degree of proportionality depended on the magnitude of AVM shunt flow. CONCLUSION: In this simulation, shunt obliteration increased pressure in the nidus and feeding arteries with little effect on the proximal circulation. The shunt provided a "buffering" effect, i.e., higher flow fistulas were exposed to smaller variations in intravascular pressure in feeding artery and nidal pressures during manipulation of systemic pressure.

Adult↗
PubMed1997

Transactivation domains facilitate promoter occupancy for the dioxin-inducible CYP1A1 gene in vivo.

We have studied the transcriptional regulation of the dioxin-inducible mouse CYP1A1 gene in its native chromosomal setting. We analyzed the ability of aromatic hydrocarbon receptor (AhR) mutants and AhR chimeras to restore dioxin responsiveness to the CYP1A1 gene in AhR-defective mouse hepatoma cells. Our data reveal that transactivation domains in AhR's C-terminal half mediate occupancy of the nuclear factor 1 site and TATA box for the CYP1A1 promoter in vivo. Transactivation domains of VP16 and AhR nuclear translocator, but not Sp1, can substitute for AhR's C-terminal half in facilitating protein binding at the promoter. Our data also reveal an apparent linear relationship between promoter occupancy and CYP1A1 gene expression in chromatin. These findings provide new insights into the in vivo mechanism of transcriptional activation for an interesting mammalian gene.

Animals↗
PubMed1997

[Expression of IL-4 and IL-10 by PBMC and tumor tissues in cancer patients].

Using biological activity assay, the production of IL-4 and IL-10 by peripheral blood mononuclear cells (PBMC) was studied in patients with nasopharyngeal carcinoma and lymphoma. The IL-2, IL-4 and IFN gamma levels in both cancer patients were lower than that in normal subjects. In contrast, the IL-10 level was higher in both cancer patients. When rIL-2 was added into the cytokine production system, IL-2, IL-4, and IFN gamma level were upregulated in lymphoma patients. However, in the patients of nasopharyneal carcinoma, only IL-2 level was upregulated. IL-10 activity could not be affected by exogenous IL-2 in both cancer patients. The results of negative IL-4 activity and higher positive percentage (84.6%) of IL-10 activity in ascites from patients with ovarian carcinoma were corresponded to the patients with nasopharyngeal carcinoma and lymphoma. By using in situ hybridization technique, the expression of IL-4 and IL-10 was studied in tumor tissues from patients with gastric, esophageal and breast carcinomas. There was no differences of the percentage of IL-4 and IL-10 expression among three kinds of tumor tissues, the range of positive percentage was 40%-70%. These results indicate that the correction of abnormal upregulation of IL-10 activity should be considered for cancer immunotherapy.

Breast Neoplasms↗
PubMed1997

[Studies on aging enzyme activities of the human dental pulp blood vessels].

Histochemical distribution and age changes of alkaline phosphatase (AKPase E. C. 3. 1. 3. 1) and adenosine triphosphatase (ATPase E. C. 3. 6. 1. 3) in normal human dental pulp blood were investigated qualitatively and quantitatively. 42 dental pulp samples from patients aged 10 to 70 years old were divided into three groups. Results showed that accompanying aging, activities of AKPase and ATPase of dental pulp blood vessels decreased. AKPase staining quantities for group one (10-30 years), group two (31-50 years) and group three (51-70 years) were 40.62 +/- 13.79, 36.75 +/- 9.78 and 19.20 +/- 5.35 and ATPase staining quantities were 33.00 +/- 10.09, 27.53 +/- 16.60 and 23.27 +/- 5.04 respectively. The endothelial cells of capillaries in dental pulp changed greatly. With aging, metabolic ability of dental pulp decreased gradually. In addition, it was observed that the capillaries in sub-odontoblasts decreased and odontoblast layer became thin with aging. The close association of the capillaries of the pulp to the odontoblasts had been demonstrated.

Adenosine Triphosphatases↗
PubMed1997

[A promoter responsible for over-expression of cholera toxin B subunit in cholera toxin A subunit structure gene].

A promoter sequence, which promotes the transcription of cholera toxin B subunit gene, was found in cholera toxin A subunit structure gene. The transcription starts at the adenine Located at +833, that is 456bp upstream to the A of the initiation codon ATG of cholera toxin B gene. Under the control of the promoter, cholera toxin B subunit was over-expressed as high as 200 mg/L at an optimized culture condition. The chloramphenicol acetyl transferase gene and beta-galactosidase could also be efficiently expressed under the direction of the promoter. This promoter may be responsible for the 6 fold and 7 fold higher expression level of cholera toxin B subunit than cholera toxin A subunit in V. cholerae and Escheria coli respectively. The over-expression of CTB may be useful in preparing vaccine against cholera and facilitating the construction of peptide-bearing immunogenic hybrid proteins.

Base Sequence↗
PubMed1997

Construction of a Salmonella typhimurium vaccine strain expressing Vibrio cholera CT-B and LPS-O antigen.

The genes encoding V. cholera CT-B and LPS-O antigens were simultaneously inserted into the vector plasmid pYA248. The resulting recombinant plasmid pMG306 was transformed into the delta cya delta crp delta asd attenuated S. typhimurium vaccine strain x4072, and the live vaccine strain x4072 (pMG306) was constructed. This vaccine strain could secrete a specific CT-B antigen. Meanwhile, LPS-O antigens of both V. cholera and S. typhimurium were expressed on the cell surface. Mouse intraperitoneal immunization and subsequent challenge trial indicated that x4072 (pMG306) provided good protection against virulent V. cholera. This study has laid the foundation for the development of a new cholera-typhoid bivalent live oral vaccine.

Agglutination Tests↗
PubMed1997

Cell lineage determination and the control of neuronal identity in the neural crest.

The molecular mechanisms underlying the determination of neuronal identity in the vertebrate peripheral nervous system are only just beginning to come into focus. Many of these mechanisms, such as the involvement of cascades of bHLH transcription factors and lateral inhibition via the Notch-Delta system, appear to have been conserved from Drosophila (Ghysen et al. 1993; Jan and Jan 1993). The way in which these genetic circuits are controlled by instructive growth factors, and the manner in which they lead to expression of a particular neuronal identity, is far from clear. This process is being elucidated by studies of neurogenesis in the peripheral autonomic lineage, which is arguably the best-understood neurogenic lineage in vertebrates. Emerging evidence is beginning to suggest that neuronal diversity within the autonomic and sensory lineages may be generated by related, but distinct, mechanisms. All autonomic progenitors express a common bHLH protein, MASH1, which appears to be induced by members of the BMP2 subfamily secreted by the tissues to which these progenitors migrate. Additional signals may then act on these progenitors in different locations to induce the expression of other transcription factors, which act in conjunction with MASH1 to specify the final phenotypes of the different autonomic neuron subtypes (sympathetic, parasympathetic, and enteric). Although different classes of autonomic neurons develop in very different locations within the body, different classes of sensory neurons are located together in dorsal root ganglia. The finding that distinct but related subtypes of bHLH proteins, the neurogenins, are expressed by different classes of sensory neuron precursors early in development suggests that sensory neuron diversity, in contrast to autonomic neuron diversity, may be pre-specified at or before the time neural crest cells begin their emigration from the neural tube.

Animals↗
PubMed1997

[Abrogated or decreased tumorigenicity and metastasis induced by retroviral-mediated B7.1 gene transfer on murine tumors with different immunogenicity].

OBJECTIVE: To investigate the differences of tumorigenicity and metastasis of marine tumors with different immunogenicity by B7.1 gene transfer. METHOD: Using retroviral-mediated gene transfer, we transduced B7.1 cDNA into a panel of murine tumor lines with different immunogenicity to study the effect of B7.1 costimulation on antitumor immunity. RESULTS: After transduced with B7.1 cDNA, the immunogenic T lymphoma EL4 regressed completely, and tumorgenicity of three nonimmunogenic tumors melanoma B16, mastocytoma P815 and mammary adenocarcinoma MA891 were significantly reduced in syngeneic mice. The experimental metastasis of B16 and spontaneous pulmonary metastasis of MA891 were profoundly suppressed. Moreover, immunization with B7.1 cDNA transduced B16 induced systemic immunity against subsequently inoculated parental B16 tumor, while this immunization method did not provide protective immunity against established parental B16 tumor. CONCLUSION: Our results show that varied extent of antitumor immunity can be induced to abrogate or decrease tumorigenecity and metastasis through B7.1 gene transduction, depending on the immunogenic potential of tumors.

Animals↗
PubMed1997

[A prospective study on respiratory symptoms and functions in new employees exposed to cotton dust].

Sixty new employees in a cotton textile mill were followed up for five years to study their occurrence of byssinosis and its natural history. Results showed that the workers complained more cough, expectoration and other respiratory irritation symptoms at their early exposure to cotton dust, and the frequency of chest tightness in them reached the peak one year after exposure and remained at higher level later. Stratified analysis showed that all the respiratory symptoms did not correlate with their smoking habits, specific body constitution, etc. Forced expiratory volume at one second (FEV1) after shift declined with length of exposure and appeared a tendency to exacerbate gradually, especially in workers with a positive skin test of cotton antigen. Smoking had no influence on it. It suggests that exposure to cotton dust and idiosyncracy of the workers play important roles in damage to lung function.

Adolescent↗
PubMed1997

[Relation of Lac promotor and the expression of cholera toxin subunit B gene in recombinant Escherichia coli MM2].

Effects of different carbon sources including glucose, lactate and acetate and IPTG induction on the expression of ctb gene, which is on the downstream of lac promotor, in recombinant Escherichia coli MM2 were studied. In medium YC were added 0.048mol/L glucose, 0.102mol/L lactate or 0.167mol/L acetate which separately produce the same energy in the condition of complete oxidization. Addition of glucose largely decreased the expression level of ctb gene because of decrease of pH during culture process. Addition of lactate increased the expression level of ctb gene by 1.15 fold and did not inhibit the growth of MM2 strain. Addition of acetate increasd the expression level of ctb gene by 0.97 fold and inhibited the growth of MM2 strain. Induction by IPTG at different time and different concentration did not increase the expression level of ctb gene, so the lac promotor had no or a little influence upon the expression of ctb gene in recombinant MM2 strain.

Acetates↗
PubMed1996

X-MyT1, a Xenopus C2HC-type zinc finger protein with a regulatory function in neuronal differentiation.

X-MyT1 is a C2HC-type zinc finger protein that we find to be involved in the primary selection of neuronal precursor cells in Xenopus. Expression of this gene is positively regulated by the bHLH protein X-NGNR-1 and negatively regulated by the Notch/Delta signal transduction pathway. X-MyT1 is able to promote ectopic neuronal differentiation and to confer insensitivity to lateral inhibition, but only in cooperation with bHLH transcription factors. Inhibition of X-MyT1 function inhibits normal neurogenesis as well as ectopic neurogenesis caused by overexpression of X-NGNR-1. On the basis of these findings, we suggest that X-MyT1 is a novel, essential element in the cascade of events that allows cells to escape lateral inhibition and to enter the pathway that leads to terminal neuronal differentiation.

Age Factors↗
PubMed1996

Identification of neurogenin, a vertebrate neuronal determination gene.

Several bHLH proteins are involved in vertebrate neurogenesis, but those controlling early stages of neuronal determination have not yet been identified. Here we describe a novel, NeuroD-related bHLH protein, NEUROGENIN, whose expression precedes that of NeuroD in both mouse and Xenopus. Expression of Xenopus NEUROGENIN-related-1 (X-NGNR-1) defines the three prospective territories of primary neurogenesis. Overexpression of X-NGNR-1 (or NEUROGENIN) induces ectopic neurogenesis and ectopic expression of XNeuroD mRNA. Endogenous X-ngnr-1 expression becomes restricted to subsets of cells by lateral inhibition, mediated by X-Delta-1 and X-Notch. The properties of X-NGNR-1 are thus analogous to those of the Drosophila proneural genes, suggesting that it functions as a vertebrate neuronal determination factor.

Amino Acid Sequence↗