PubMed Health⌕ Search

Biomedical subjects

W T Cheng

Publications and source records attributed to W T Cheng.

24 records · Page 2Linked to original sources
PubMed1992

Unregulated and basal transcriptional activities of the regulatory sequence of the type 18 human papillomavirus genome in transgenic mice.

Type 18 human papillomavirus (HPV18) is a genital virus closely associated with cervical carcinoma. To analyze the transcriptional activities of the long control region (LCR) of the HPV18 genome, we have produced 12 transgenic mice harboring the HPV18/LCR sequence fused to a promoterless SV40 T-antigen (TAg) gene. The mice were small in body size, generally very weak, and none lived longer than 110 days. Three mice with the longest life span (58-110 days) developed hyperplastic thymus and/or lymph node and were further analyzed. In these mice, Northern hybridization failed to detect TAg transcripts in any of the 25 organs studied. However, spliced TAg RNA was detected by polymerase chain reaction in the hyperplastic thymus and lymph node and in the normal submaxillary gland, stomach, large intestine, urinary bladder, and the cerebrum, indicating the presence of very low cellular levels of TAg RNA in these organs. When immunostaining was performed on the hyperplastic thymus, TAg protein was detected only in the ductal epithelial cells. Our results appear to indicate that the HPV18/LCR sequence was able to express only unregulated and basal levels of transcriptional activity in transgenic mice. Such a mode of transcription has become a major hindrance in the use of transgenic mouse system for the studies of the biology of the human papillomavirus.

Amino Acid Sequence↗
PubMed1991

Transgenome transcription and replication in the liver and extrahepatic tissues of a human hepatitis B virus transgenic mouse.

We have produced a transgenic mouse (B32-1) carrying the complete genome of the human hepatitis B virus (HBV). High titers of the viral surface (HBsAg) and the e antigen (HBeAg) were detected in the serum of the mouse. In the liver and 12 of 16 extrahepatic tissues analyzed, Northern blot hybridization indicated the presence of the 2.1-kilobase (kb) and the 3.5-kb major HBV transcripts. A liver cDNA library was constructed from which the liver RNAs from four cDNA clones with splicing were found. Sequencing analysis showed that the splicing occurred between nucleotides 2451 and 487 of the viral genome, resulting in a truncated viral polymerase gene, as in human hepatocytes. Southern blot analysis of total DNA preparations of the tissues revealed the presence of episomal HBV genome, indicating replication of the viral transgenome in these tissues. However, replication was detected only in some but not all of the tissues that transcribed the 3.5-kb RNA. Partial double-stranded as well as full-length and subgenomic-length single-stranded HBV DNA species of discrete sizes were detected which may represent replication intermediates of preferred replication termination sites of the HBV transgenome. Since many molecular characteristics of mouse B32-1 were similar to those found in HBV-infected humans, HBV transgenic mice similar to B32-1 would be useful in further elucidation of other aspects of the replication and transcription mechanisms of HBV in the liver and extrahepatic tissues.

Animals↗
PubMed1991

The occupational exposure level of 1,2-dichloroethane in an EM preparation laboratory.

The toxicity of 1,2-Dichloroethane, DCE, toxicity was measured in an Electron-Microscopy (EM) preparation laboratory by Gas Chromatography. Although the personal exposure of the worker to DCE has not exceeded the occupational exposure limits, the exposure level was quite close to the short-term exposure limit. Owing to the carcinogenic potential and low exposure limits of DCE, it is suggested that a closed controlled-environment would be useful in reducing the exposure level of DCE.

Air Pollutants, Occupational↗
PubMed1985

Limited proteolysis of the porcine zona pellucida by homologous sperm acrosin.

Boar sperm acrosin isolated by affinity chromatography on p-(p'-aminophenoxypropoxy)benzamidine linked to Sepharose was tested for its proteolytic effect on the zona pellucida of freshly ovulated pig eggs. During 1 h in a physiological medium there was no observable change in the morphology of the zona pellucida but subsequent 125I labelling of the structure followed by electrophoretic analysis revealed that acrosin had asserted a limited and selective proteolysis.

Acrosin↗
PubMedDate not supplied

Severe acute respiratory syndrome: 'SARS' or 'not SARS'.

Accurate clinical diagnosis of severe acute respiratory syndrome (SARS) based on the current World Health Organization definition is difficult and at times impossible at the early stage of the disease. Both false positive and false negative cases are commonly encountered and this could have far-reaching detrimental effects on the patients, their family and the clinicians alike. Contact history is particularly important in diagnosing SARS in children as their presenting features are often non-specific. The difficulty in making a correct diagnosis is further compounded by the lack of a sensitive rapid diagnostic test. Serology is not particularly helpful in the initial triaging of patients as it takes at least 3 weeks to become positive. Co-infection and other treatable conditions should not be missed and conventional antibiotics should remain as part of the first-line treatment regimen. We report five cases to illustrate the difficulties and dilemmas faced by clinicians in diagnosing SARS in children.

Adolescent↗