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Biomedical subjects

M Xu

Publications and source records attributed to M Xu.

At least 361 records · Page 20Linked to original sources
PubMed1992

cdc25+ encodes a protein phosphatase that dephosphorylates p34cdc2.

To determine how the human cdc25 gene product acts to regulate p34cdc2 at the G2 to M transition, we have overproduced the full-length protein (cdc25Hs) as well as several deletion mutants in bacteria as glutathione-S-transferase fusion proteins. The wild-type cdc25Hs gene product was synthesized as an 80-kDa fusion protein (p80GST-cdc25) and was judged to be functional by several criteria: recombinant p80GST-cdc25 induced meiotic maturation of Xenopus oocytes in the presence of cycloheximide; p80GST-cdc25 activated histone H1 kinase activity upon addition to extracts prepared from Xenopus oocytes; p80GST-cdc25 activated p34cdc2/cyclin B complexes (prematuration promoting factor) in immune complex kinase assays performed in vitro; p80GST-cdc25 stimulated the tyrosine dephosphorylation of p34cdc2/cyclin complexes isolated from Xenopus oocyte extracts as well as from overproducing insect cells; and p80GST-cdc25 hydrolyzed p-nitrophenylphosphate. In addition, deletion analysis defined a functional domain residing within the carboxy-terminus of the cdc25Hs protein. Taken together, these results suggest that the cdc25Hs protein is itself a phosphatase and that it may function directly in the tyrosine dephosphorylation and activation of p34cdc2 at the G2 to M transition.

Animals↗
PubMed1992

Inducible phytoalexins in juvenile soybean genotypes predict soybean looper resistance in the fully developed plants.

The hypocotyl of different soybean genotypes was tested for its inducible phytoalexin (i.e. glyceollin or coumestrol) accumulation and its inducible soybean looper resistance in response to chemical elicitation. A very highly insect-resistant soybean genotype (PI 227687) produced significantly more phytoalexins than a relatively insect-susceptible one (Davis) in response to the same chemical elicitation. The resultant standardized hypocotyl assay allowed quick categorization of unknown soybean genotypes regarding the level of insect resistance in the fully developed plants. Glyceollin was a better indicator of inducible resistance than coumestrol. Elicitor concentration influenced the amount of glyceollin and coumestrol accumulated. Younger seedlings (4-5 d old) responded stronger to chemical elicitation than did older ones (7-10 d old). The elicited accumulation of glyceollin showed a temporal pattern that peaked at 72 h. Accumulation of coumestrol showed a gradual increase. Elicitation of phytoalexins in juvenile soybean plants by sulfhydryl-binding reagents was found to be useful for the prediction of genotypic differences in the level of insect resistance in the fully developed plants.

Journal Article↗
PubMed1992

Chinese medical school exit objectives: a multi-institutional survey of teacher opinion.

This paper describes a collaborative survey of Chinese medical school teacher opinion concerning clinical behaviours and skills that Chinese students should be expected to demonstrate prior to graduation from medical school. Selected teachers from four Chinese medical schools indicated whether each of 77 objectives was: essential for every student to know or demonstrate prior to graduation; useful but not essential; or not applicable to their educational programmes. Results show teachers' expectations regarding some of the behaviours and skills Chinese medical school teachers consider to be important for students to learn. Forty-nine per cent of the exit objectives were regarded as essential by 75% or more of the teachers. The most essential objectives involved performing clinical procedures, collaborating and communicating with health care professionals, conducting organ system examinations, formulating hypotheses and defining problems. Other essential objectives were concerned with communicating with patients and their families, maintaining currency within the discipline, and recognition, evaluation and triage of patients with life-threatening or chronic conditions. Exit objectives related to health promotion and risk assessment were regarded as useful but not essential at the undergraduate level. Implications for Chinese medical education are discussed.

China↗
PubMed1992

Fluid transport across cultured bovine corneal endothelial cell monolayers.

The mammalian corneal endothelium is known to transport fluid from the stromal compartment to the aqueous humor, thereby maintaining corneal transparency. Corneal endothelial cells have been cultured for some years now, but whether they preserve their in vivo ability to actively transport fluid is not known. We have now grown bovine corneal endothelial cell monolayers (BCECM) on permeable substrates (Transwell) and report that, just like their counterparts in vivo, these cultured cells pump fluid from the basal to the apical compartment and display measurable electrical resistance and potential difference across the monolayer. BCECM were grown on collagen-treated permeable supports using Dulbecco's modified Eagle's medium (DMEM)/20% fetal bovine serum with antibiotics. Cells grew to confluence in 5-7 days and displayed polygonal shape. Only cells from passages 1-3 were utilized. Inserts were fitted directly into Lucite chambers specially built. The rate of fluid pumping by BCECM was 3.96 +/- 0.49 (SE) microliter.h-1.cm-2 (n = 13) and could be measured continuously for several hours; fluid pumping was inhibited by 0.2 mM amiloride. The specific electrical resistance of the monolayers was 180 +/- 22 omega.cm2 (n = 11). A mean electrical potential difference of 63.8 +/- 3.7 microV (n = 15, range 40-100 microV, apical side negative) was recorded across the monolayers in DMEM. The availability of the commercial inserts makes this procedure practical; as a consequence, the rate of fluid transport by cultured corneal endothelium has been quantitated for the first time. This method can now be extended to other cultured layers.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗
PubMed1992

[A computer program for the power spectra analysis of biomedical signals].

This paper presents a useful program for the power spectra analysis of biomedical signals on a microcomputer. The frequency spectra to show the allocation of frequency were calculated from the acquired biomedical signal via a window algorithm and the real signal special handling. The frequency spectra became normalized power spectra through algorithm and could be displayed on a monitor or printer in the mode of histogram. We have got good results using this program to compute the power spectra of phrenic nerve discharges from the rabbit.

Algorithms↗
PubMed1992

[A computerized analysis of phrenic nerve discharge signal].

The authors offered a method of computerized analysis to solve the problems met in the manual measurement of the signal of phrenic nerve discharge (PND). An envelope was gained via digital fullwave rectification and filter from the acquired PND signal. From it, some important parameters were measured automatically. The program ran well in animal experiments. The values of the PND parameters obtained by computer showed no significant difference as compared with the averaged values measured manually by researchers.

Animals↗
PubMed1992

In situ dephosphorylation of p53 protein by calf intestinal alkaline phosphatase treatment.

The monoclonal antibody (mAb) 1801 has been reported to identify an N-terminal determinant within the tumor-suppressor protein p53 located between amino acids 32 and 79. This region contains two potential sites for serine phosphorylation at amino acids 33 and 46. Using a novel technique which dephosphorylates proteins in situ in fixed permeabilized cells, we have unmasked determinants in p53 recognized by mAb 1801, allowing additional sites of p53 protein to be detected in immunohistochemically reacted cells. This result indicates that phosphorylation at one or both sites within the determinant recognized by mAb 1801 previously blocked antibody-ligand interaction. It further suggests that in situ dephosphorylation may be of more general use in identifying antibodies which can only bind to epitopes in a particular phosphorylation state.

Alkaline Phosphatase↗
PubMed1992

[Experimental autoimmune lesions of the inner ear].

This paper presents the autoimmune lesions of the inner ear by using isologous inner ear antigen (IEAg) on the guinea pigs. The purposes of this study were to determine whether the inner ear is an immune response organ and what is the sequelae of the immune processes both on physiological and morphological changes in the inner ear. Animals were systemically sensitized with IEAg in complete Freund's adjuvant and boothed with IEAg in incomplete Freund's adjuvant three times in every 3-4 weeks and then allowed to survive 4-6 weeks. For the ABR measurement, 8 of 28 ears (28.6%) in the experimental group showed threshold enhancement greater than or equal to 10dB before the animal sacrifice and the mean threshold shift of the ABR 8 weeks post immunization and before sacrifice revealed significant difference. Histological specimens were processed for both light and electron microscopic study. In the LM study, it showed endolymphatic hydrops, local thickening of the Reissener's membrane, and spiral ganglion cells lost. In the SEM, disturbance and loss of the cilia of the outer hair cells of the cochlea and the type I and II sensory cells in the crista ampularis can be seen. Also, some otoconia showed numerous malformation.

Animals↗
PubMed1991

Mucin production by colon cancer cells cultured in serum-free medium.

Although many colon cancer cell lines are available for study, few of them exhibit differentiated properties. When cultured in medium containing fetal bovine serum, WiDr cells (WiDr-FBS) show an undifferentiated phenotype: growth as a multilayer of cells adherent to plastic and lack of polarization, brush border, and mucin vacuoles. In contrast, WiDr cells cultured in a chemically-defined serum-free medium containing insulin, transferrin and selenium (WiDr-ITS) grow as clusters of nonadherent cells with abundant desmosomes and tight junctions, microvilli and electron-lucid vacuoles. As WiDr-FBS cells, WiDr-ITS are not polarized. WiDr-ITS cells show a marked enhancement in mucin synthesis as demonstrated by: periodic acid-Schiff and Alcian blue stains, electron microscopy, immunohistochemistry using monoclonal antibodies (MAbs) reactive with mucin-associated epitopes, immune electron microscopy and immunochemical analysis using Western blots. In comparison with WiDr-FBS cells, WiDr-ITS cells showed strong expression of Tn, sialyl-Tn, blood group A and CEA. When mouse MAbs were used, higher levels of the MUCI gene product were detected in WiDr-ITS than in WiDr-FBS cells. The full spectrum of phenotypic changes was observed after I month of culture in ITS medium, and transfer of WiDr-ITS cells to FBS medium was accompanied by a partial phenotypic reversal, suggesting that these phenotypic changes result from an adaptative--rather than selective--process.

Alcian Blue↗
PubMed1991

Determination of basal acetylcholine release in vivo by rat brain dialysis with a U-shaped cannula: effect of SM-10888, a putative therapeutic drug for Alzheimer's disease.

A U-shaped dialysis cannula was implanted into rat frontal cortex, hippocampus and striatum, and after 1 day for surgical recovery the cannula was perfused with Ringer's solution without any acetylcholinesterase (AChE) inhibitor under freely moving conditions. With a highly sensitive assay method for acetylcholine (ACh), the basal ACh content in the dialysates were detectable in those brain regions for several hours. The basal levels in the frontal cortex, hippocampus and striatum were 82 +/- 9, 72 +/- 4, 70 +/- 8 fmol/20 microliters (mean +/- S.E.M.), respectively. When SM-10888, a novel AChE inhibitor and putative therapeutic drug for Alzheimer's disease, was injected intraperitoneally, ACh in the dialysate of the cortex increased in a dose-dependent manner. Changes in the levels of hippocampal and striatal ACh release evoked by SM-10888 were similar to, but smaller than, that in the cortex. These data suggest that since the present assay method is able to determine in vivo basal ACh release in the dialysate without any AChE inhibitor, it is possible to study the effect of a novel drug such as SM-10888 in the brain regions.

Acetylcholine↗