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Biomedical subjects

S T Liang

Publications and source records attributed to S T Liang.

At least 19 recordsLinked to original sources
PubMed2000

Response of nasopharyngeal carcinoma cells to Epstein-Barr virus infection in vitro.

Many nasopharyngeal carcinoma (NPC) biopsy specimens contain Epstein-Barr virus (EBV). However, the response of NPC cells to EBV infection in vitro and in vivo is not well characterized. In this experiment we infected NPC cells with EBV particles through endocytosis of a complex of EBV immunoglobulin A (IgA) secretory component (SC) protein to observe the response of host cells to the foreign viral infection in vitro. We found that EBV particles were endocytosed and stabilized in NPC nuclei 24 hours after infection; the EBV genomes were then gradually decreased after serial passages within 3 to 4 weeks by the following pathway: the EBV genomes first moved toward the nuclear envelope from the center of the nucleus; after crossing the nuclear envelope, they moved into the cytoplasm and toward the plasma membrane and were discharged by exocytosis. At the 10th day of EBV infection, EBV-latent membrane protein-1 and Epstein-Barr nuclear antigen (EBNA)-1 protein expressions could be detected, but not EBV-viral capsid antigen. Observation of EBNA-1 protein and host growth factor and cytokine gene expressions in the weeks after incubation revealed that the EBNA-1 protein expression was decreased proportionally with decrease of EBV genome. The mRNA expression of epithelial growth factor receptor, transforming growth factor (TGF)-alpha, interleukin (IL)-1beta, IL-6, and granulocyte-macrophage colony-stimulating factor increased within 1 to 2 weeks after infection, and gradually recovered to the original level at 3 to 4 weeks, whereas the mRNAs of TGFbeta1, TGFbeta receptor type I (TGFbetaRI), TGFbetaR type II, IL-8, and tumor necrosis factor-alpha remained unchanged. It is concluded that in vitro EBV infection in NPC cells results in increase of certain growth factor and cytokine gene expressions in host cells. The change in gene expression returns to the original level approximately 3 to 4 weeks after infection because of exocytosis of EBV DNA by the infected cells through an unidentified mechanism.

Base Sequence↗
PubMed2000

mRNA composition and control of bacterial gene expression.

The expression of any given bacterial protein is predicted to depend on (i) the transcriptional regulation of the promoter and the translational regulation of its mRNA and (ii) the synthesis and translation of total (bulk) mRNA. This is because total mRNA acts as a competitor to the specific mRNA for the binding of initiation-ready free ribosomes. To characterize the effects of mRNA competition on gene expression, the specific activity of beta-galactosidase expressed from three different promoter-lacZ fusions (P(spc)-lacZ, P(RNAI)-lacZ, and P(RNAII)-lacZ) was measured (i) in a relA(+) background during exponential growth at different rates and (ii) in relA(+) and DeltarelA derivatives of Escherichia coli B/r after induction of a mild stringent or a relaxed response to raise or lower, respectively, the level of ppGpp. Expression from all three promoters was stimulated during slow exponential growth or at elevated levels of ppGpp and was reduced during fast exponential growth or at lower levels of ppGpp. From these observations and from other considerations, we propose (i) that the concentration of free, initiation-ready ribosomes is approximately constant and independent of the growth rate and (ii) that bulk mRNA made during slow growth and at elevated levels of ppGpp is less efficiently translated than bulk mRNA made during fast growth and at reduced levels of ppGpp. These features lead to an indirect enhancement in the expression of LacZ (or of any other protein) during growth in media of poor nutritional quality and at increased levels of ppGpp.

Bacterial Proteins↗
PubMed1999

Decay of rplN and lacZ mRNA in Escherichia coli.

To examine the previously proposed retroregulation model of spc mRNA degradation, two strains of Escherichia coli B/r were used; one has wild-type spc and lac operons and the other has a lac operon deletion, a wild-type spc operon, and a Pspc-rplN-lacZ fusion operon lacking the normal control sites of the spc operon (rplN is the first gene in the spc operon of ribosomal proteins). The decay of rplN mRNA and of lacZ mRNA in these strains was determined during exponential growth at different rates and after transcript initiation was inhibited by the antibiotic rifampicin. Functional decay of lacZ mRNA was monitored by measurements of beta-galactosidase activity and chemical decay was monitored using probes complementary to rplN, rplX, and to the 5' and 3'-terminal sections of lacZ. Analysis of the data was based on the assumption that the decay involves an endonucleolytic cleavage that functionally inactivates the mRNA and that this is followed by exonucleolytic degradation of the cleavage products. The major conclusions were: (1) During exponential growth, lacZ mRNA of the lac operon was translated about twice as frequently as lacZ mRNA of the spc-lac fusion, and both kinds of lacZ mRNA were translated at an elevated rate in the presence of rifampicin. (2) For lacZ mRNA from the lac operon, the endonuclease inactivation reaction was not affected by rifampicin, but the exonuclease reaction was inhibited. (3) The decay of rplN mRNA from the spc operon was accelerated in the presence of rifampicin; the average life was estimated to be six minutes during exponential growth in LB medium, and 2.8 minutes in the presence of rifampicin. (4) The decay of the rplN section of mRNA from the spc-lac operon fusion was coupled to the decay of the downstream lacZ mRNA section and was strongly inhibited (i.e. partially blocked) in the presence of rifampicin. These results show that the decay of spc mRNA differs in some important aspects from the decay of lac mRNA and support the retroregulation model. Moreover, the results indicate that rifampicin can have a significant and selective impact on the kinetics of both mRNA translation and decay.

Escherichia coli↗
PubMed1998

Expression of lacZ from the promoter of the Escherichia coli spc operon cloned into vectors carrying the W205 trp-lac fusion.

The expression of lacZ has been analyzed and compared in a series of promoter cloning vectors by measuring the amount of lacZ mRNA by hybridization and the amount of beta-galactosidase by standard enzymatic assay. Expression was driven by the promoter, Pspc, of the spc ribosomal protein operon. The vectors contained either the standard W205 trp-lac fusion with the trp operon transcription terminator, trpt, located in the lacZ leader sequence, or a deletion derivative that functionally inactivates trpt. In the presence of trpt, lacZ expression was temperature dependent so that increasing the growth temperature reduced the accumulation of lacZ mRNA and beta-galactosidase activity. The frequency of transcript termination at trpt was estimated to be near zero at 20 degreesC and at about 45% at 37 degreesC. The amount of Pspc-derived lacZ mRNA and the amount of beta-galactosidase produced per lacZ mRNA varied, depending on the mRNA 5' leader sequence between Pspc and lacZ. These results demonstrate that the quantitative assessment of promoter activities with promoter cloning vectors requires careful analysis and interpretation. One particular construct without trpt did not seem to contain fortuitous transcription or translation signals generated at the fusion junction. In this strain, lacZ expression from Pspc was compared at the enzyme activity and mRNA levels with a previously constructed strain in which lacZ was linked to the tandem P1 and P2 promoters of the rrnB operon. At any given growth rate, the different activities of beta-galactosidase in these two strains were found to reflect the same differences in their amounts of lacZ mRNA. Assuming that the promoter-lacZ fusions in these strains reflect the properties of the promoters in their normal chromosomal setting, it was possible to estimate the absolute transcription activity of Pspc and the relative translation efficiency of Pspc-lacZ mRNA at different growth rates. Transcription from the spc promoter was found to increase from about 10 transcripts per min at a growth rate of 1.0 doublings/h to a maximum plateau of about 23 transcripts per min at growth rates above 1.5 doublings/h. The translation frequency of lacZ mRNA expressed from Pspc was unaffected by growth rates.

Artificial Gene Fusion↗
PubMed1988

Contribution of prematurity and low birth-weight to neonatal death in Chinese and Western populations.

This paper analyses the contribution of low birth-weight (birth-weight between 500 and 2,500 g) and prematurity (gestation less than 37 weeks) to neonatal death in Chinese and Western populations. The incidences of low birth-weight in the Tsan Yuk Hospital, Hong Kong, the State of Victoria, and the Mercy Maternity Hospital, Melbourne, were 4.63%, 4.29% and 5.66% respectively and the incidences of prematurity were 2.08%, 4.89% and 7.42% respectively. The neonatal mortality rate (per 1,000 livebirths) for premature infants born in Victoria was 64, 89 for those born at the Mercy Maternity Hospital and 119 for the Tsan Yuk Hospital. This paper has demonstrated that a striking differences exists in prematurity rates between Chinese and Western populations, and also that the mortality rate of premature infants is lower in Western populations. If the reason for the lower incidence of prematurity in the Chinese population could be determined and the mortality of premature infants maintained in the Western population, a significant lowering of perinatal mortality would result. Studies to determine causes for premature births in Chinese and Western populations should therefore be undertaken.

China↗
PubMed1987

Ultrasound evaluation of pregnancies at risk for homozygous alpha-thalassaemia-1.

Twenty-six pregnant Chinese women who were at risk of giving birth to a fetus affected with homozygous alpha-thalassaemia-1 were examined serially by ultrasound. Six of these 26 pregnancies were affected. In one third of the affected pregnancies progressive fetal ascites appeared before 24 weeks gestation and these pregnancies were terminated. In the remaining two thirds abnormal estimated fetal weight-placental volume (EFW-PV) ratio and fetal growth retardation as evidenced by a falling biparietal diameter (BPD), femur length (FL) but a normal abdominal circumference (AC) was apparent by 28 weeks gestation. Increased transverse cardiac (TC) diameter was another consistent finding but appeared late. All these features appeared before the onset of fetal ascites. A normal EFW-PV ratio and fetal growth until 28 weeks gestation was a reassuring sign of normality. Abnormal EFW-PV ratio was the earliest sign to appear in affected pregnancies and a normal ratio until 28 weeks gestation had a 100 per cent predictive value.

Female↗
PubMed1987

Characteristic pattern of Doppler umbilical arterial velocity waveform in conjoint twins.

Doppler blood flow studies in a pair of conjoint twins at 18 weeks gestation revealed a characteristic 'double layer' spectral velocity waveform from the umbilical arteries. This is the result of signals originating from 2 separate arterial supplies adjacent to each other in a single umbilical cord. Such a characteristic feature provides an additional sonographic sign in the diagnosis of conjoint twins.

Adult↗
PubMed1987

Doppler blood flow velocity waveforms in alpha-thalassemia hydrops fetalis.

Doppler shift blood flow velocity-time waveforms in the umbilical arteries (UA), aorta (A), and inferior vena cava (IVC) in eight fetuses with alpha-thalassemia (alpha-thal) hydrops fetalis were described. The UA waveforms in these fetuses with anemia in utero depicted a hyperdynamic circulatory state with a relative increase in acceleration slope, more linear decline from maximum systole to end diastole, and reduced spectral broadening. The aortic waveforms similarly displayed distorted systolic peaks, flow turbulence, and greatly elevated diastolic frequencies. Reversal of end diastolic flow in the IVC also indicated cardiac decompensation in these fetuses. Progressive changes in these waveforms were apparent in two fetuses that had serial evaluation. In another four fetuses in which alpha-thal major was diagnosed in the second trimester by DNA analysis and had Doppler evaluation before termination of pregnancy, consistent changes in the UA, A, and IVC waveforms were not observed. This study confirms the potential usefulness of Doppler spectral waveforms in depicting altered hemodynamic changes in the fetus and in the evaluation of hydrops fetalis. Doppler ultrasound examination can be included as part of the routine workup of hydrops fetalis.

Aorta, Thoracic↗
PubMed1987

Significance of an absent or reversed end diastolic flow in Doppler umbilical artery waveforms.

The outcome of nine fetuses in whom Doppler umbilical arterial velocity-time waveforms showed absence or reversal of flow in end diastole was presented. Eight of the nine resulted in either intrauterine or neonatal death. Progressive deleterious changes in the waveforms were evident in three fetuses who had serial evaluation. The remaining infant survived when delivery was expected 2 days later. Our data have indicated that the demonstration of an absent or reversed flow in end diastole in the umbilical arteries carries with it a very specific indication of serious fetal compromise and the need for immediate delivery, although the prognosis of a normal neonatal survival remains guarded.

Blood Flow Velocity↗
PubMed1987

Middle cerebral artery Doppler flow velocity waveforms.

Doppler flow velocity-time waveforms of the middle cerebral arteries at their origin from the internal carotid arteries were obtained serially on 14 patients to determine the alterations of these waveforms with gestational age. Satisfactory recordings were obtained from all patients. The middle cerebral artery waveforms demonstrated a typically biphasic pattern with continuing forward flow in diastole. The peak systolic to end-diastolic ratio (A/B ratio) showed a progressive and significant decline from 6.89 +/- 1.48 at around 25 weeks to 4.23 +/- 0.67 at term. Elevation of diastolic velocities and diminished A/B ratio in the middle cerebral arteries were noted in four fetuses, in whom severe antepartum compromise was diagnosed. The ratio also appeared to decrease with worsening of fetal condition. Because the fetus compensates for hypoxia by increasing blood flow to the brain, Doppler middle cerebral artery waveforms may permit evaluation of fetal compromise and hypoxia.

Blood Flow Velocity↗
PubMed1986

Trisomy 18: the value of late prenatal diagnosis.

Diagnosis of trisomy 18 was made in 2 fetuses late in pregnancy. Both pregnancies were complicated by polyhydramnios coexisting with fetal growth retardation. The significance of these findings, and the advantages and limitations of late prenatal diagnosis of fetal chromosomal abnormality are discussed.

Adult↗
PubMed1986

Perinatal colonization of group B streptococcus--an epidemiological study in a Chinese population.

An epidemiological study of perinatal colonization of group B streptococcus (GBS) was carried out prospectively in a Chinese population. One hundred and sixty-eight mother-infant pairs were studied. Maternal carriage rate from multiple sites was 19.0%, with an overall neonatal colonization rate of 19.6%. There was no neonatal sepsis due to GBS. No obstetrical risk factors that could influence material carriage could be identified. Neonatal colonization was associated with premature/prolonged rupture of membranes, increased duration of rupture of membranes and intrapartum pyrexia. The number of infected sites and the density of organism in each site in the infant were directly proportional to the number and density of organisms in the culture-positive sites in the mother. Serotypical study showed a complete absence of type II GBS in this population. Since the vertical transmission rate was only 37.5%, it is postulated that nosocomial spread of the organism contributed significantly towards colonization of the infants in our study population.

Carrier State↗
PubMed1986

[Occult lung cancer with positive cytology and normal chest film--an analysis of 54 cases].

From 1973 to 1980 and 1982 to 1984, mass annual screening was carried out in Yunnan Tin Corporation. Chest X-ray and sputum cytology were used to detect lung cancer among subjects with an underground work history over 10 years and over 40 years of age. 54 cases of occult lung cancer with positive cytology and negative X-ray plain film were found, 48 out of 100,725 subjects and 6 out ot 8,808 out-patients. 42 lesions were located by bronchoscopy and 12 by various roentgenologic examinations. Among these 54 cases, 52 (96.3%) were central type lung cancers. Squamous cell carcinoma was found in 53 and small cell anaplastic carcinoma in only 1. Diagnosis was established by pathology in 35 and by cytology in 19. In 18 cases treated by surgery, there were 15 Ia stage and 3 Ib (UICC staging system). 3 Ib died of recurrence 33, 62 and 101 months after operation. 1 Ia died of residual cancer recurrence 21 months after sleeve-resection. The overall 5 year survival rate was 91.6% (11/12). The authors believe that X-ray plain films sometimes fail to detect the early stage central type lung cancers. Bronchoscopy, in particular fiberoptic bronchoscopy is one of the most effective means in diagnosis and location. By bronchoscopy, in general, the tumor could be detected and the extent of involvement in the bronchus assessed. Finally, the authors emphasize that mass screening is a useful method to detect early lung cancer among the high risk population.

Adult↗
PubMed1985

Homozygous alpha-thalassaemia: clinical presentation, diagnosis and management. A review of 46 cases.

Forty-six hydropic infants with homozygous alpha-thalassaemia born during a period of 10 years have been reviewed. The incidence was 1:1550 total births, and accounted for 81% of all non-immune hydrops. The male to female ratio was 1:1.4. There was increased incidence of anaemia, pregnancy induced hypertension, antepartum haemorrhage, malpresentation, prematurity, fetal distress, difficult vaginal delivery, caesarean section, retained placenta, postpartum haemorrhage and congenital abnormalities. Antenatal diagnosis by DNA hybridization with subsequent abortion of the affected fetuses is the best method to decrease maternal morbidity and to reduce the incidence of hydrops fetalis in couples at risk. For those with no previous history, but with early onset hypertension and/or polyhydramnios, sonography is useful in making an earlier diagnosis, and in reducing avoidable morbidity, because DNA analysis can be done before caesarean section and aggressive neonatal management is instituted.

Adolescent↗
PubMed1985

Zinc deficiency is not a cause for abortion, congenital abnormality and small-for-gestational age infant in Chinese women.

Zinc concentration in serum and hair was measured in a cross-sectional study of 437 Chinese women of whom 310 were normal controls studied at various stages of pregnancy and up to 12 months after delivery. The rest had spontaneous abortions, fetuses with a birthweight below the 10th centile for gestation or congenital abnormalities. Zinc concentration fell throughout normal pregnancy, the fall being greater in serum than in hair. There was no correlation between serum and hair levels. The infant birthweight had a positive correlation with serum level but a negative correlation with hair level. Abortion, low birthweight and congenital abnormality were not associated with low concentrations of zinc in plasma or hair.

Abortion, Spontaneous↗
PubMed1985

Aetiological factors in the genesis of pregnancy hydronephrosis.

In order to identify possible aetiological factors in the genesis of physiological hydronephrosis in pregnancy, the degree of pelvic-calyceal dilatation in 90 asymptomatic pregnant women was correlated with levels of plasma oestradiol, progesterone, 24-hour urinary oestriol, the site of the placenta, birthweight of the fetus, and pelvic inlet measurements. A grading system based on maximum calyceal diameter was used; 90% of the patients were found to have at least mild dilatation on the right side. No correlation was demonstrated between the degree of hydronephrosis and the levels of oestradiol, progesterone and 24-hour urinary oestriol excretion. The birth-weight of the fetus and its relationship with the pelvic inlet measurements also did not correlate with the occurrence of hydronephrotic changes in the kidneys. The only significant positive finding was a higher incidence of moderate and severe hydronephrosis occurring in patients with a right-sided placenta than compared with the left (x2 = 4.77; p less than 0.05), although the sensitivity and specificity in predicting hydronephrosis from a right-sided placenta is low (53% and 66% respectively). Our results support the hypothesis of a mechanical aetiology in the genesis of pregnancy hydronephrosis, where vascular compression on the ureters may be an important contributory factor. Our study has also shown that urinary tract infection and reduction of creatinine clearance were not more common in patients with moderate or severe pelvic-calyceal dilatation.

Bacteriuria↗