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J Ma

Publications and source records attributed to J Ma.

At least 415 records · Page 23Linked to original sources
PubMed1996

A gene map of the human genome.

The human genome is thought to harbor 50,000 to 100,000 genes, of which about half have been sampled to date in the form of expressed sequence tags. An international consortium was organized to develop and map gene-based sequence tagged site markers on a set of two radiation hybrid panels and a yeast artificial chromosome library. More than 16,000 human genes have been mapped relative to a framework map that contains about 1000 polymorphic genetic markers. The gene map unifies the existing genetic and physical maps with the nucleotide and protein sequence databases in a fashion that should speed the discovery of genes underlying inherited human disease. The integrated resource is available through a site on the World Wide Web at http://www.ncbi.nlm.nih.gov/SCIENCE96/.

Amino Acid Sequence↗
PubMed1996

A prospective study of triglyceride level, low-density lipoprotein particle diameter, and risk of myocardial infarction.

OBJECTIVE: To test whether a predominance of small, dense low-density lipoprotein (LDL) particles and elevated triglyceride levels are independent risk factors for myocardial infarction (MI). DESIGN: Nested case-control study with prospectively collected samples. SETTING: Prospective cohort study. PARTICIPANTS: Blood samples were collected at baseline (85% nonfasting samples) from 14916 men aged 40 to 84 years in the Physicians' Health Study. MAIN OUTCOME MEASUREMENTS: Myocardial infarction diagnosed during 7 years of follow-up. RESULTS: Cases (n=266) had a significantly smaller LDL diameter (mean [SD], 25.6 [0.9] nm) than did controls (n=308) matched on age and smoking (mean [SD], 25.9 [8] nm; P<.001). Cases also had higher median triglyceride levels (1.90 vs 1.49 mmol/L [168 vs 132 mg/dL]; P<.001). The LDL diameter had a high inverse correlation with triglyceride level (r=-0.71), and a high direct correlation with high-density lipoprotein cholesterol (HDL-C) level (r=0.60). We observed a significant multiplicative interaction between triglyceride and total cholesterol (TC) levels (P=.01). After simultaneous adjustment for lipids and a variety of coronary risk factors, LDL particle diameter was no longer a statistically significant risk indicator, with a relative risk (RR) of 1.09 (95% confidence interval [CI], 0.85-1.40) per 0.8-nm decrease. However, triglyceride level remained significant with an RR of 1.40 (95% CI, 1.10-1.77) per 1.13 mmol/L (100-mg/dL) increase. The association between triglyceride level and MI risk appeared linear across the distribution; men in the highest quintile had a risk about 2.5 times that of those in the lowest quintile. The TC level, but not HDL-C level, also remained significant, with an RR of 1.80 (95% CI, 1.44-2.26) per 1.03-mmol/L (40-mg/dL) increase. CONCLUSIONS: These findings indicate that nonfasting triglyceride levels appear to be a strong and independent predictor of future risk of MI, particularly when the total cholesterol level is also elevated. In contrast, LDL particle diameter is associated with risk of MI, but not after adjustment for triglyceride level. Increased triglyceride level, small LDL particle diameter, and decreased HDL-C levels appear to reflect underlying metabolic perturbations with adverse consequences for risk of MI; elevated triglyceride levels may help identify high-risk individuals.

Adult↗
PubMed1996

A PCR-based DNA fingerprinting technique: AFLP for molecular typing of bacteria.

Amplified restriction fragment polymorphism (AFLP) is a PCR-based DNA fingerprinting technique. In AFLP analysis, bacterial genomic DNA is digested with restriction enzymes, ligated to adapters, and a subset of DNA fragments are amplified using primers containing 16 adapter defined sequences with one additional arbitrary nucleotide. Polymorphisms of different Escherichia coli strains or Agrobacterium tumefaciens strains were demonstrated as distinct, unique bands in a denaturing sequencing gel using AFLP. The polymorphisms detected between BL21 and BL21F'IQ and between DH5 alpha and DH5 alpha F'IQ strains indicated that AFLP is able to resolve differences in F' episomal DNA (approximately 100 kb).

Agrobacterium tumefaciens↗
PubMed1996

Sequences outside the homeodomain of bicoid are required for protein-protein interaction.

The Drosophila morphogenetic protein Bicoid (Bcd) is required for the development of anterior structures of the embryo. Bcd, a homeodomain protein, is distributed as an anterior-to-posterior gradient in the embryo. It stimulates the expression of the hunchback (hb) gene in the anterior half in an all-or-none fashion. We have recently shown that Bcd binds cooperatively to a hb enhancer element and proposed that cooperative DNA binding is facilitated by an interaction between Bcd molecules. In this report, we further analyze the interaction between Bcd molecules and define regions important for protein-protein interaction. We show that the homeodomain of Bcd alone fails to interact with another Bcd molecule efficiently. The protein sequence flanking either side of the homeodomain restores the protein-protein interaction function. Mutations in the homeodomain that affect DNA binding do not adversely affect the protein-protein interaction function, suggesting that the surfaces for DNA binding and protein-protein interaction are separable. Finally, we demonstrate that the homeodomain of Bcd alone, unlike the intact Bcd, fails to bind DNA cooperatively. These results further support the notion that cooperative DNA binding is facilitated by the interaction between Bcd molecules. They strongly suggest that protein-protein interaction is an important property of Bcd for its biological activities.

DNA Footprinting↗
PubMed1996

Prospective study of sex hormone levels and risk of prostate cancer.

BACKGROUND: Sex steroids, particularly androgens, have been implicated in the pathogenesis of prostate cancer. Data from previous studies comparing circulating hormone levels in men with and without prostate cancer are difficult to interpret, since the studies were limited in size, hormone levels were analyzed in blood drawn after the diagnosis of cancer, nonrepresentative control subjects were used, and hormone and hormone-binding protein levels were not simultaneously adjusted. PURPOSE: We conducted a prospective, nested case-control study to investigate whether plasma hormone and sex hormone-binding globulin (SHBG) levels in healthy men were related to the subsequent development of prostate cancer. METHODS: Among participants in the Physicians' Health Study who provided plasma samples in 1982, we identified 222 men who developed prostate cancer by March 1992. Three hundred ninety control subjects, matched to the case patients on the bases of age, smoking status, and length of follow-up, were also identified. Immunoassays were used to measure the levels of total testosterone, dihydrotestosterone (DHT), 3 alpha-androstanediol glucuronide (AAG), estradiol, SHBG, and prolactin in the stored (at -82 degrees C) plasma samples. Correlations between individual hormone levels and between hormone levels and SHBG in the plasma of control subjects were assessed by use of Spearman correlation coefficients (r). Odds ratios (ORs) and 95% confidence intervals (CIs) specifying the prostate cancer risk associated with quartile levels of individual hormones, before and after adjustment for other hormones and SHBG, were calculated by use of conditional logistic regression modeling. Reported P values are two-sided. RESULTS: No clear associations were found between the unadjusted levels of individual hormones or SHBG and the risk of prostate cancer. However, a strong correlation was observed between the levels of testosterone and SHBG (r = .55), and weaker correlations were detected between the levels of testosterone and the levels of both estradiol (r = .28) and DHT (r = .32) (all P < .001). When hormone and SHBG levels were adjusted simultaneously, a strong trend of increasing prostate cancer risk was observed with increasing levels of plasma testosterone (ORs by quartile = 1.00, 1.41, 1.98, and 2.60 [95% CI = 1.34-5.02]; P for trend = .004), an inverse trend in risk was seen with increasing levels of SHBG (ORs by quartile = 1.00, 0.93, 0.61, and 0.46 [95% CI = 0.24-0.89]; P for trend = .01), and a non-linear inverse association was found with increasing levels of estradiol (ORs by quartile = 1.00, 0.53, 0.40, and 0.56 [95% CI = 0.32-0.98]; P for trend = .03). No associations were detected between the levels of DHT or prolactin and prostate cancer risk; for AAG, a marker of 5 alpha-reductase activity, only suggestive evidence of a positive association was found. The results were essentially unchanged when case patients diagnosed within 4 years of plasma collection, case patients diagnosed with localized (i.e., nonaggressive) disease, or control subjects with elevated prostate serum antigen levels (> 2.5 ng/mL) were excluded from the analyses. CONCLUSIONS: High levels of circulating testosterone and low levels of SHBG-both within normal endogenous ranges-are associated with increased risks of prostate cancer. Low levels of circulating estradiol may represent an additional risk factor. Circulating levels of DHT and AAG do not appear to be strongly related to prostate cancer risk.

Adult↗
PubMed1996

In vitro studies on cellular and molecular mechanisms of arsenic trioxide (As2O3) in the treatment of acute promyelocytic leukemia: As2O3 induces NB4 cell apoptosis with downregulation of Bcl-2 expression and modulation of PML-RAR alpha/PML proteins.

It has been shown recently in China that arsenic trioxide (As2O3) is a very effective treatment for acute promyelocytic leukemia (APL). APL patients resistant to all-trans retinoic acid (ATRA) and conventional chemotherapy can still respond to AS2O3. In this study, we addressed the possible cellular and molecular mechanisms of this treatment by using NB4 cells as a model. The results show that: (1) As2O3 triggers relatively specific NB4 cell apoptosis at micromolar concentration, as proved by morphology, histogramic related nuclear DNA contents, and DNA gel eletrophoresis. (2) As2O3 does not influence bax, bcl-x, c-myc, and p53 gene expression, but downregulates bcl-2 gene expression at both mRNA and protein levels. (3) As2O3 induces a significant modulation of the PML staining pattern in NB4 cells and HL-60 cells. The micropunctates characteristic of PML-RAR alpha in NB4 cells dissappear after treatment with As2O3, whereas a diffuse PML staining occurs in the perinuclear cytoplasmic region. In addition, a low percentage of untreated NB4 cells exhibits an accumulation of PML positive particles in a compartment of cytoplasm. The percentage of these cells can be significantly increased after As2O3 treatment. A similar PML staining pattern is observed in apoptotic cells. (4) ATRA pretreatment does not influence As2O3-induced apoptosis. These results suggest that induction of cell apoptosis can be one of the mechanisms of the therapeutic effect of As2O3. Moreover, this apoptosis induction occurs independently of the retinoid pathway and may be mediated, at least partly, through the modulation of bcl-2, as well as PML-RAR alpha and/ or PML proteins.

Apoptosis↗
PubMed1996

Autoimmune lpr/lpr mice deficient in CD40 ligand: spontaneous Ig class switching with dichotomy of autoantibody responses.

Fas-deficient MRL/Mp-lpr/lpr mice develop a syndrome that resembles human systemic lupus erythematosus, including production of IgG autoantibodies against small nuclear ribonucleoproteins (snRNPs), dsDNA, and self IgG (rheumatoid factor). To investigate the necessity for T-B cell contact in MRL autoimmunity, mice deficient in CD40 ligand (CD40L) were backcrossed onto this background, and Ab synthesis was assessed. In comparison to their CD40L-intact lpr/lpr counterparts, CD40L-deficient lpr/lpr mice had elevated levels of serum IgM and lower levels of IgG; however, a subset of animals had IgG2a, and to a lesser extent, IgG2b levels similar to those found in wild-type lpr/lpr mice. Levels of both isotypes in CD40L-deficient lpr/lpr mice were significantly greater than those found in nonautoimmune CD40L-deficient animals. IgG autoantibodies, including those directed against small nuclear ribonucleoproteins, also arose in CD40L-deficient lpr/lpr mice; however, they did not develop IgG rheumatoid factors or anti-dsDNA, and lacked histologic evidence of overt glomerulonephritis at age 3 mo, in contrast to CD40L-intact lpr/lpr animals. These results indicate that isotype switching occurs in lpr/lpr mice deficient in CD40L, and that production of IgG autoantibodies to ribonucleoproteins is at least partially preserved. They also suggest that different mechanisms may be responsible for eliciting autoantibody responses in lpr/lpr mice.

Animals↗
PubMed1996

Immunization with T cell receptor V beta chain peptides deletes pathogenic T cells and prevents the induction of collagen-induced arthritis in mice.

Collagen-induced arthritis (CIA) in susceptible strains of mice is an animal model of T cell-mediated inflammatory polyarthritis. Analysis of T cell receptor (TCR) V beta gene usage in cells isolated from arthritic joints of BUB/BnJ (BUB) mice (H-2q, TCR V beta a) showed that TCR V beta chain gene usage was limited to TCR V beta 3 and V beta 10 gene families. All of the BUB mice immunized with a mixture of TCR V beta 3 and TCR V beta 10 peptides, but not with control TCR V beta 14 peptide, were refractory to the induction of CIA. Immunization with TCR V beta 3 and V beta 10 peptides completely blocked the development of clinical and subclinical inflammation, formation of pannus and synovial hyperplasia, and the erosion of cartilage and bone. Further studies revealed that preimmunization of BUB mice with V beta 10 peptide alone was sufficient to render the mice resistant to CIA. Analysis of TCR V beta chain gene expression in lymph node cells from arthritic and arthritis-protected mice showed the expression of TCR V beta 10 subfamily in all of the arthritic mice, but not in arthritis-protected mice. Immunization with TCR V beta peptides did not diminish the humoral responses to chicken type-II collagen and also elicited significant levels of anti-V beta 3 and anti-V beta 10 peptide antibodies. Antibodies cross-reactive with mouse chicken type-II collagen were detected in both the arthritic and arthritis-protected mice. Adoptive transfer of serum from arthritis-protected BUB mice significantly delayed the onset (P < 0.005) of arthritis in recipient BUB mice. In contrast, mice injected with serum from arthritic mice had early onset of arthritis. These results demonstrate that immunization of BUB mice with TCR V beta chain peptides elicited antibodies reactive with the self-TCR and prevented the induction of collagen-induced arthritis by eliminating or downregulating pathogenic T cells and consequently blocking the development of humoral immune response. These findings may have clinical applications in treating human autoimmune diseases characterized by common TCR gene usage.

Amino Acid Sequence↗
PubMed1996

Negative regulatory element involved in the hormonal regulation of GlcNAc-1-P transferase gene in mouse mammary gland.

The gene encoding UDP-GlcNAc:dolichol phosphate N-acetylglucosamine-1-phosphate transferase (GPT), the enzyme that initiates the pathway for the biosynthesis of asparagine-linked glycoproteins, is ubiquitously expressed in eukaryotic cells. However, its expression in the mammary gland is developmentally and hormonally regulated; transcription of the mouse mammary GPT gene is stimulated by the lactogenic hormones, insulin, glucocorticoid, and prolactin. The involvement of cisacting elements in regulating the expression of the mouse GPT (mGPT) gene was investigated by transient transfections of various GPT promoter/luciferase (Luc) constructs into primary mouse mammary epithelial cells. A series of 5'-deletions of the GPT promoter identified a distal negative regulatory region (base pairs -1057 to -968) and deletion of this region results in enhanced hormonal induction (approximately 7-fold) with no effect on basal promoter activity. Electrophoretic mobility shift assays (EMSA) performed with nuclear extracts from different developmental stages of mouse mammary gland demonstrated that the binding activity of the nuclear proteins to the distal negative regulatory region was predominant in virgin stage as compared with pregnant and lactating stages. EMSA performed with nuclear extracts from virgin explants showed that the binding activity was markedly decreased after cultivation with the combination of the three lactogenic hormones. DNase I footprinting analysis identified two pentamer direct repeat motifs, AGGAA and GAAAC, within the negative regulatory region. EMSA competition experiments showed that mutations within the direct repeats failed to compete for binding of the nuclear proteins to labeled wild type oligonucleotide. Transcription from the promoter containing the mutated direct repeats was increased greatly, consistent with the conclusion that these motifs functions in vivo to repress GPT gene expression. These data suggest the importance of the negative regulatory region in hormonal control of mGPT gene expression in mammary gland.

Animals↗
PubMed1996

Phosphorylation-dependent block of cystic fibrosis transmembrane conductance regulator chloride channel by exogenous R domain protein.

The cystic fibrosis transmembrane conductance regulator (CFTR) constitutes a linear conductance chloride channel, which is regulated by cAMP-dependent protein kinase phosphorylation at multiple sites located in the intracellular regulatory (R) domain. Studies in a lipid bilayer system, reported here, provide evidence for the control of CFTR chloride channel by its R domain. The exogenous R domain protein (encoded by exon 13 plus 85 base pairs of exon 14) interacted specifically with the CFTR molecule and inhibited the chloride conductance in a phosphorylation-dependent manner. Only the unphosphorylated R domain protein blocked the CFTR channel. Such functional interaction suggests that the putative gating particle of the CFTR chloride channel resides in the R domain.

Base Sequence↗
PubMed1996

A disulfide-bonded dimer of the Golgi beta-galactoside alpha2,6-sialyltransferase is catalytically inactive yet still retains the ability to bind galactose.

The alpha2,6-sialyltransferase is a terminal glycosyltransferase localized in the trans Golgi and trans Golgi network. Here we show that 30% of the total rat liver Golgi alpha2,6-sialyltransferase forms a disulfide-bonded 100-kDa species that can be converted to the 50-kDa monomer form of the enzyme upon reduction. Limited proteolysis of both enzyme forms demonstrates that the 100-kDa species is a disulfide-bonded homodimer of the alpha2,6-sialyltransferase. The alpha2,6-sialyltransferase disulfide-bonded dimer is found in bovine liver Golgi membranes and in Golgi membranes prepared and solubilized in the presence of 100 mM iodoacetamide, suggesting that it is not unique to rat liver or formed aberrantly upon membrane lysis. The dimer form of the enzyme possesses no significant catalytic activity and has a much lower affinity for CDP-hexanolamine-agarose compared with the monomer form. In contrast, both the alpha2,6-sialyltransferase monomer and the disulfide-bonded dimer bind strongly to galactose and galactose-terminated substrates. These results suggest that the alpha2,6-sialyltransferase disulfide-bonded dimer lacks catalytic activity due to a weak affinity for its sugar nucleotide donor, CMP-NeuAc, and that this catalytically inactive form of the enzyme may act as a galactose-specific lectin in the Golgi.

Animals↗
PubMed1996

Expression, purification, and mechanistic studies of bovine mitochondrial translational initiation factor 2.

A complete cDNA clone encoding bovine mitochondrial translational initiation factor 2 (IF-2mt) has been obtained. The regions of the cDNA corresponding to mature IF-2mt and several of its functional domains have been expressed in Escherichia coli as histidine-tagged proteins. The precursor (approximately 90 kDa) and mature (approximately 85 kDa) forms of IF-2mt are toxic to E. coli and can only be expressed at low levels. Shorter forms of this factor (approximately 80 and approximately 72 kDa) are also found during the expression of mature IF-2mt. The various forms of IF-2mt can be separated by high performance liquid chromatography. All of these forms are active in promoting the GTP-dependent binding of formyl-Met-tRNA to the small subunit of either E. coli or bovine mitochondrial ribosomes. IF-2mt can bind to mitochondrial ribosomes in the absence of GTP, initiator tRNA, or messenger RNA. The presence of GTP stimulates IF-2mt binding to ribosomes about 3-fold. IF-2mt interacts only weakly with GTP or with the initiator tRNA in the absence of ribosomes. Molecular dissection of IF-2mt shows that a long deletion (approximately 150 amino acid residues) from the NH2-terminal region does not affect its activity in vitro. The COOH domain of IF-2mt (amino acid residues 332-727) can bind to ribosomes even though it does not promote initiator-tRNA binding.

Amino Acid Sequence↗
PubMed1996

Sequence of the Saccharomyces cerevisiae YTP1 gene encoding a deduced novel type-III integral membrane protein with domains of sequence similarity to mitochondrial electron-transport enzymes.

The nucleotide sequence is reported for the Saccharomyces cerevisiae YTP1 (yeast putative transmembrane (TM) protein) gene, encoding a novel deduced protein of 459 amino acids (aa) in length (51 643 Da). The Ytp1 protein appears by computer analysis (hydropathy plots in conjunction with the combined predictions of several Internet on-line programs that deduce protein structure from primary sequence data) to be a type-III integral TM protein containing 10 or 11 TM-spanning domains. Blocks of aa sequence similarity, predominantly to mitochondrial electron transport proteins, are consistent with the notion that Ytp1 is an integral TM protein and may reflect some aspect of its functional role. The C terminus of Ytp1 is both hydrophilic and highly negatively charged, with 11 of the last 33 aa corresponding to Glu or Asp. Although Northern blot analysis indicates that this gene is expressed, a disruption of YTP1 shows that it is not essential. YTP1 is located between SIN4 (TSF3) and KEX2 (SRB1) at position 205 (kb) on the chromosome XIV physical map.

Amino Acid Sequence↗
PubMed1996

Fast 3D large-angle spin-echo imaging (3D FLASE).

A rapid steady-state 3D spin-echo imaging pulse sequence, based on the principle of nutating the spins by an angle greater than 90 degrees, has been designed and implemented on a clinical 1.5-T whole-body MR scanner. The pulse sequence, denoted fast large-angle spin-echo (FLASE), has been optimized for high-resolution imaging of tissues with short T2 and T2*. Features of FLASE include a minimum-phase Shinnar-Le Roux excitation pulse and distribution of phase- and slice-encoding gradients before and after the 180 degrees refocusing pulse to minimize the critical time delay between inversion and restoration of the residual longitudinal magnetization and for minimizing echo time. A Bloch equation analysis, corroborated by experimental data, shows FLASE signal-to-noise to be superior to its closest analog, 3D rapid spin-echo excitation (RASEE) (Jara et al., Magn Reson Medicine 29, 528 (1993)), and 3D gradient-recalled acquisition in steady state (GRASS). It is demonstrated that with judicious RF phase-cycling and steady state operation, FLASE can produce high-quality microimages free of intravoxel phase dispersion from susceptibility-induced background gradients. The performance of the method is exemplified with ultra high-resolution images of trabecular bone in vitro and in vivo in the human calcaneus and wrist at voxel sizes as low as 98 x 98 x 200 microns3. Finally, the contrast behavior of refocused FLASE can be altered by disrupting the steady state analogous to gradient echo imaging.

Bone and Bones↗
PubMed1996

Localization of the hemochromatosis disease gene: linkage disequilibrium analysis using an American patient collection.

The genetic basis of idiopathic hemochromatosis, a common disorder of iron metabolism, has remained an enigma for over two decades. In an attempt to refine the chromosomal localization of this gene, we have conducted a linkage disequilibrium mapping study utilizing a large group of unrelated American patients. The 12 microsatellites used as genetic markers in this analysis include a series of recently described polymorphic dinucleotide (D6S1558, D6S1545 and D6S1554) and tetranucleotide (D6S1016 and D6S1281) repeats which map between D6S105 and D6S299. Haplotype reconstructions indicate that a core genotype, composed of D6S464 allele 3/D6S1260 allele 4/D6S1558 allele 5, exists on a majority of disease chromosomes. Stringent statistical measures of marker-disease disequilibrium suggest that only associations with D6S1260 are significant and furthermore, aid in the assignment of refined centromeric and telomeric limits for the likely location of the hemochromatosis gene. In summary, the genetic data presented in this report predict that the hemochromatosis locus resides between D6S464 and D6S1558, most likely very close to marker D6S1260. Because a single yeast artificial chromosome clone contains all three of the above loci, a thorough search for coding sequences in this region is likely to identify the gene mutated in this common disorder.

Chromosome Mapping↗
PubMed1996

Method for image-based measurement of the reversible and irreversible contribution to the transverse-relaxation rate.

A multislice NMR imaging pulse sequence capable of measuring both the reversible and irreversible contribution to the transverse-relaxation rate (R'2 and R2) in a single scan is described. The method, termed GESFIDE (gradient-echo sampling of FID and echo) is based on sampling the descending and ascending portions of a Hahn echo with a train of gradient echoes. R2 and R'2 are computed by exploiting the differential evolution of the transverse magnetization before and after the phase-reversal pulse. Salient features of the method are its insensitivity to RF pulse imperfections and its high precision and efficiency. Applications examined involve the characterization of magnetically inhomogeneous tissues and biomaterials such as trabecular bone marrow in the skeleton and brain iron.

Bone Marrow↗