PubMed Health⌕ Search

Biomedical subjects

F Chang

Publications and source records attributed to F Chang.

At least 19 recordsLinked to original sources
PubMed2001

A mechanism for nuclear positioning in fission yeast based on microtubule pushing.

The correct positioning of the nucleus is often important in defining the spatial organization of the cell, for example, in determining the cell division plane. In interphase Schizosaccharomyces pombe cells, the nucleus is positioned in the middle of the cylindrical cell in an active microtubule (MT)-dependent process. Here, we used green fluorescent protein markers to examine the dynamics of MTs, spindle pole body, and the nuclear envelope in living cells. We find that interphase MTs are organized in three to four antiparallel MT bundles arranged along the long axis of the cell, with MT plus ends facing both the cell tips and minus ends near the middle of the cell. The MT bundles are organized from medial MT-organizing centers that may function as nuclear attachment sites. When MTs grow to the cell tips, they exert transient forces produced by plus end MT polymerization that push the nucleus. After an average of 1.5 min of growth at the cell tip, MT plus ends exhibit catastrophe and shrink back to the nuclear region before growing back to the cell tip. Computer modeling suggests that a balance of these pushing MT forces can provide a mechanism to position the nucleus at the middle of the cell.

Cell Cycle↗
PubMed2001

Evaluation of the hydrogen bonding interactions and their effects on the oxidation-reduction potentials for the riboflavin complex of the Desulfovibrio vulgaris flavodoxin.

The oxidation-reduction potentials for the riboflavin complex of the Desulfovibrio vulgaris flavodoxin are substantially different from those of the flavin mononucleotide (FMN) containing native protein, with the midpoint potential for the semiquinone-hydroquinone couple for the riboflavin complex being 180 mV less negative. This increase has been attributed to the absence in the riboflavin complex of unfavorable electrostatic effects of the dianionic 5'-phosphate of the FMN on the stability of the flavin hydroquinone anion. In this study, 15N and 1H-15N heteronuclear single-quantum coherence nuclear magnetic resonance spectroscopic studies demonstrate that when bound to the flavodoxin, (1) the N1 of the riboflavin hydroquinone remains anionic at pH 7.0 so the protonation of the hydroquinone is not responsible for this increase, (2) the N5 position is much more exposed and may be hydrogen bonded to solvent, and (3) that while the hydrogen bonding interaction at the N3H appears stronger, that at the N5H in the reduced riboflavin is substantially weaker than for the native FMN complex. Thus, the higher reduction potential of the riboflavin complex is primarily the consequence of altered interactions with the flavin ring that affect hydrogen bonding with the N5H that disproportionately destabilize the semiquinone state of the riboflavin rather than through the absence of the electrostatic effects of the 5'-phosphate on the hydroquinone state.

Binding Sites↗
PubMed2001

Cardiac memory in canine atrium : identification and implications.

BACKGROUND: Memory is a diverse biological phenomenon whose importance in the ventricle has been demonstrated. We hypothesized its occurrence in the atrium, contributing to the modulation of cardiac rhythm. METHODS AND RESULTS: We analyzed P and Ta waves in conscious chronically instrumented dogs with complete heart block. Animals were atrioventricularly sequentially paced at 5% greater than the sinus rate from the lateral right atrium (RA) during control, followed by 2 periods of 1-hour test pacing at 50% greater than the sinus rate, or by equivalent test pacing from the left atrial appendage (LAA) at 5% or 50% greater than the sinus rate. Recovery RA pacing periods of 20- and 30-minute duration, respectively, succeeded each test pacing period. RA test pacing at either rate did not affect the variables measured, but changing the pacing site from RA to LAA altered the P and Ta waves. Displacement of the spatial atrial gradient vector occurred during recovery from LAA pacing, was more marked at rapid pacing rates, and manifested accumulation and resolution consistent with cardiac memory. Concurrently, the right effective refractory period decreased. CONCLUSIONS: Memory is demonstrable in canine atrium, showing rapid onset, accumulation during successive pacing periods, and resolution on cessation of pacing. Given its association with a reduced effective refractory period, it may contribute to the substrate for atrial arrhythmias.

Animals↗
PubMed2001

Risk for respiratory distress syndrome in preterm infants born to mothers complicated by placenta previa.

This study examined the risk factors for respiratory distress syndrome (RDS) in preterm infants from pregnancies complicated by placenta previa. Forty preterm infants born to mothers with placenta previa between January 1989 and December 1995 in a medical center were enrolled. Each of these patients was matched in gestational age and gender with an infant born immediately after to a mother without placenta previa. Obstetric and neonatal outcome variables were collected. The mean+/-S.D. gestational age for both groups was 33.0+/-3.1 weeks. There was no difference in mean birthweight between the placenta previa and control groups (2129+/-598 vs. 2136+/-493 g). All the patients in the former and 11 (28%) in the latter were born by cesarean section. About a half of the mothers in both groups received antenatal steroids. Infants from placenta previa pregnancies had a higher incidence (21/40 vs. 10/40, P<0.01) and more severe RDS than controls. Stratified by the status of treatment with antenatal steroid, we found that gestational age was a significant risk factor for RDS in both treated and untreated groups (P<0.01), but placenta previa was an independent risk factor (odds ratio 32; CI 1-4182) by multiple exact logistic regression in antenatal steroid-treated group. We conclude that preterm infants born to mothers with placenta previa had a higher risk for RDS than controls. It played an independent role, in addition to gestational age, only in infants treated with antenatal steroid. We speculate that placenta previa was not directly contributing to RDS, but through other associated risk factors for RDS.

Adrenal Cortex Hormones↗
PubMed2001

Role of actin polymerization and actin cables in actin-patch movement in Schizosaccharomyces pombe.

Factors that are involved in actin polymerization, such as the Arp2/3 complex, have been found to be packaged into discrete, motile, actin-rich foci. Here we investigate the mechanism of actin-patch motility in S. pombe using a fusion of green fluorescent protein (GFP) to a coronin homologue, Crn1p. Actin patches are associated with cables and move with rates of 0.32 microm s(-1) primarily in an undirected manner at cell tips and also in a directed manner along actin cables, often away from cell tips. Patches move more slowly or stop when actin polymerization is attenuated by Latrunculin A or in arp3 and cdc3 (profilin) mutants. In a cdc8 (tropomyosin) mutant, actin cables are absent, and patches move with similar speed but in a non-directed manner. Patches are sites of Arp3-dependent F-actin polymerization in vitro. Rapid F-actin turnover rates in vivo indicate that patches and cables are maintained continuously by actin polymerization. Our studies give rise to a model in which actin patches are centres for actin polymerization that drive their own movement on actin cables using Arp2/3-based actin polymerization.

Actin-Related Protein 2↗
PubMed2000

Microtubule and actin-dependent movement of the formin cdc12p in fission yeast.

Although a number of gene products involved in cytokinesis have been identified, still little is known about how these proteins are localized to the proper site and assembled into a ring structure. How is the plane of cell division is positioned in the cell? Schizosaccharomyces pombe are simple rod-shaped eukaryotic cells that divide by medial fission using a medial contractile ring. S. pombe cdc12p encodes a member of the formin gene family, proteins with conserved roles in cytokinesis and actin organization. cdc12p is required specifically for the formation of the medial ring and is located in this ring during mitosis. Time-lapse microscopy of cells expressing GFP-cdc12p protein fusions reveals that during interphase, S. pombe cdc12p is present in a discrete, motile cytoplasmic particle that moves using both actin and microtubules. At the onset of mitosis, the spot moves to the future site of cell division and spreads out into a ring. These studies demonstrate that a cytokinesis factor may travel on both microtubule and actin networks to the site of contractile ring assembly. These findings suggest a potential mechanism for how the mitotic spindle positions the cell division plane in animal cells.

Actins↗
PubMed2000

Fetal renal volume in normal gestation: a three-dimensional ultrasound study.

To establish a reference chart of fetal kidneys in normal pregnancy, we performed a prospective and cross-sectional study. A total of 152 singleton fetuses ranging between 20 and 40 weeks' gestation and meeting the criteria of normal pregnancies were included. Three-dimensional ultrasound (3-D US) was used to measure the fetal renal volume. Our results revealed that both renal volumes are highly correlated with the fetal gestational age. Using gestational age (GA) as the independent variable and right renal volume (RRV) as the dependent variable, the best-fit regression equation was RRV (mL)=0.74053xGA (week)-13.318 (r = 0.89, p < 0.001). Similarly, the best-fit equation for the left renal volume (LRV) was LRV (mL)=0. 76093xGA (week)-13.421 (r = 0.86, p < 0.001). The normal growth centiles of both kidneys were established based on these two equations. There were no significant differences of the volumes between bilateral kidneys. In conclusion, our data of fetal renal volumes assessed by 3-D US may serve as a reference in evaluating fetal renal growth.

Cross-Sectional Studies↗
PubMed2000

Structural priming as implicit learning: a comparison of models of sentence production.

Structural priming reflects a tendency to generalize recently spoken or heard syntactic structures to different utterances. We propose that it is a form of implicit learning. To explore this hypothesis, we developed and tested a connectionist model of language production that incorporated mechanisms previously used to simulate implicit learning. In the model, the mechanism that learned to produce structured sequences of phrases from messages also exhibited structural priming. The ability of the model to account for structural priming depended on representational assumptions about the nature of messages and the relationship between comprehension and production. Modeling experiments showed that comprehension-based representations were important for the model's generalizations in production and that nonatomic message representations allowed a better fit to existing data on structural priming than traditional thematic-role representations.

Cognition↗
PubMed2000

Synergy between Raf and BCL2 in abrogating the cytokine dependency of hematopoietic cells.

The Raf oncoprotein plays critical roles in the transmission of mitogenic signals from cytokine receptors to the nucleus. There are three Raf family members: A-Raf, B-Raf and Raf-1. Conditionally active forms of the Raf proteins were created by ligating N-terminal truncated activated forms to the estrogen-receptor (ER) hormone-binding domain resulting in beta-estradiol-inducible constructs. We introduced these chimeric deltaRaf:ER oncoproteins into the murine FDC-P1 hematopoietic cell line. Two different types of cells were recovered after drug selection in medium containing either cytokine or beta-estradiol: (1) cytokine-dependent cells that expressed the deltaRaf:ER oncoproteins; and (2) Raf-responsive cells that grew in response to the deltaRaf:ER oncoprotein. Depending upon the particular deltaRaf:ER oncoprotein, cytokine-dependent cells were recovered 10(3) to 10(5) times more frequently than Raf-responsive cells. To determine whether BCL2 could synergize with the deltaRaf:ER oncoproteins and increase the frequency of cytokine-independent cells, cytokine-dependent deltaRaf:ER-expressing cells were infected with either a BCL2 containing retrovirus or an empty retroviral vector. BCL2 overexpression, by itself, did not relieve cytokine dependency of the parental cell line. However, BCL2 overexpression increased the frequency of Raf-responsive cells approximately five- to 100-fold. Cytokine-dependent deltaRaf:ER-infected cells entered the G1 phase of the cell cycle after cytokine withdrawal and entered S phase only after cytokine addition. Raf-responsive deltaRaf:ER cells entered the G1 phase of the cell cycle after estrogen deprivation and re-entered the cell cycle after addition of either IL-3 or the estrogen receptor antagonist tamoxifen which activates the deltaRaf:ER constructs. Expression of the BCL2 oncoprotein often delayed the exit from the S and G2/M phases demonstrating the protective effects BCL2 provided to these Raf and BCL2 infected cells. The deltaRaf:ER cells expressed the deltaRaf:ER proteins and downstream MEK and ERK activities after beta-estradiol treatment. Raf-responsive cells that were also infected with BCL2 expressed higher levels of BCL2 than the cells that were not infected with BCL2. Thus BCL2 can synergize with the activated Raf in the abrogation of cytokine dependency of certain hematopoietic cells. These cells will be useful in furthering our understanding of the roles of the Raf and BCL2 oncoproteins in hematopoietic cell growth, cell cycle progression and prevention of apoptosis.

Apoptosis↗
PubMed2000

Combined effects of aberrant MEK1 activity and BCL2 overexpression on relieving the cytokine dependency of human and murine hematopoietic cells.

The MEK1 oncoprotein plays a critical role in Ras/Raf/MEK/MAPK-mediated transmission of mitogenic signals from cell surface receptors to the nucleus. In order to examine this pathway's role in leukemic transformation, a conditionally active (beta-estradiol-inducible) form of the MEK1 protein was created by ligating a cDNA encoding an N-terminal truncated form of MEK1 to the hormone-binding domain of the estrogen receptor (ER). We introduced this chimeric deltaMEK1:ER oncoprotein into cytokine-dependent human TF-1 and murine FDC-P1 hematopoietic cell lines. Two different types of cells were recovered after drug selection in medium containing either cytokine or beta-estradiol: (1) cells that expressed the deltaMEK1:ER oncoprotein but remained cytokine-dependent and (2) MEK1-responsive cells that grew in response to deltaMEK1:ER activation. Cytokine-dependent cells were recovered 10(2) to 10(4) times more frequently than MEK1-responsive cells depending upon the particular cell line. To determine whether BCL2 overexpression could synergize with the deltaMEK1:ER oncoprotein in relieving cytokine dependence, the cytokine-dependent deltaMEK1:ER-expressing cells were infected with a BCL2-containing retrovirus, and the frequency of MEK1-responsive cells determined. BCL2 overexpression, by itself, did not relieve cytokine dependency of the parental cells, however, it did increase the frequency at which MEK1-responsive cells were recovered approximately 10-fold. DeltaMEK1:ER+BCL2 cells remained viable for at least 3 days after estradiol deprivation, whereas viability was readily lost upon withdrawal of beta-estradiol in the MEK1-responsive cells which lacked BCL2 overexpression. The MAP kinases, ERK1 and ERK2 were activated in response to deltaMEK1:ER stimulation in both deltaMEK1:ER and deltaMEK1:ER+BCL2 cells. As compared to the cytokine-dependent deltaMEK1:ER and BCL2 infected cells, MEK1-responsive BCL2 infected cells expressed higher levels of BCL2. While both MEK1-responsive deltaMEK1:ER and deltaMEK1:ER+BCL2 infected cells expressed cDNAs encoding the autocrine cytokine GM-CSF, more GM-CSF cDNAs and bioactivity were detected in the MEK1-responsive deltaMEK1:ER+BCL2 cells than in the MEK1-responsive cells lacking BCL2 or cytokine-dependent cells. These conditionally transformed cells will be useful in furthering our understanding of the roles MEK1 and BCL2 play in the prevention of apoptosis in hematopoietic cells.

Animals↗
PubMed2000

Human papillomavirus involvement in esophageal carcinogenesis in the high-incidence area of China. A study of 700 cases by screening and type-specific in situ hybridization.

BACKGROUND: Human papillomavirus (HPV) DNA has been identified in esophageal precancerous lesions and carcinomas. However, there are marked variations in the prevalence of HPV infection reported in different studies. Most previous studies on HPV and esophageal carcinomas have been based on a limited number of biopsy samples studied by different HPV detection methods with highly variable sensitivity and specificity, making systematic studies of larger series clearly warranted. METHODS: A series of 1876 surgical specimens (primary tumor, adjacent epithelium, regional lymph nodes, resection margins) from 700 patients surgically resected for an invasive squamous cell carcinoma of the esophagus in the high-incidence area of China was analyzed for the presence of HPV DNA with screening in situ hybridization (ISH) using biotinylated HPV DNA probes and followed by type-specific ISH for HPV 6, 11, 16, 18, 30, and 53. RESULTS: Of the 700 esophageal carcinomas, 118 (16.9%) were shown to contain HPV DNA sequences by screening ISH. Positive signals were most frequent in the cancer cells (16.6%), more rare in the surrounding hyperplastic and dysplastic epithelia (5.6%), and infrequently present in the resection margins (0.2%). HPV signals were also detected in cancer cells in 6.9% of the lymph node metastases. HPV types 6, 11, 16, 18, and 30 account for 39.8% of the HPV-positive lesions, of which the high-risk types HPV 16 and 18 were present in 27.1% (32 of 118). Notably, 60.2% of the HPV-positive lesions contained DNA sequences other than HPV types 6, 11, 16, 18, 30, and 53. CONCLUSIONS: This study reports the largest series of esophageal cancers ever analyzed for the presence of HPV DNA. Our results confirm the presence of common mucosal HPV types in esophageal carcinomas but also suggest the involvement of other (novel?) HPV types that are unusually detected in genital cancers in a significant proportion of these lesions. The results further indicate that HVP has an etiologic role in esophageal carcinogenesis, at least in the high-incidence area of northern China.

Biopsy↗
PubMed2000

Analysis of mid1p, a protein required for placement of the cell division site, reveals a link between the nucleus and the cell surface in fission yeast.

mid1 is required for the proper placement of the contractile actin ring for cytokinesis at a medial site overlying the nucleus. Here we find that mid1 protein (mid1p) shuttles between the nucleus and a cortical medial broad band during interphase and early mitosis. The position of this broad band, which overlies the nucleus, is linked to nuclear position even in cells with displaced or multiple nuclei. We identified and created mutations in an NLS and in two crm1-dependent NES sequences in mid1p. NES mutations caused mid1p accumulation in the nucleus and loss of function. An NLS mutations greatly reduced nuclear localization but did not perturb cytoplasmic localization or function. mid1p localization to the medial broad band was also not dependent on mid1p PH domain or microtubule and actin cytoskeletons. Overexpression of mid1p produced ectopic cell growth at this band during interphase and abnormal karmellae-like nuclear membrane structures. In plo1-1, mid1p formed a medial broad band but did not incorporate into a tight ring, suggesting that polo kinase plo1p is required for activation of mid1p function. Thus, the mid1p broad band defines a compartment at the medial cell surface, whose localization is linked to the position of the nucleus, and whose function may be to position the plane of cell division.

Actins↗
PubMed1999

Tandem duplication polymorphism upstream of the dopamine D4 receptor gene (DRD4).

The dopamine D4 receptor (DRD4) is a member of the D2-like dopamine receptor family. Polymorphisms at the DRD4 gene have been examined for association with a wide range of neuropsychiatric disorders and normal behavioral variation. The DRD4 gene is unusual in its high amount of expressed polymorphism in humans. Here we study the identification of a polymorphic tandem duplication of 120 bp located 1.2 kb upstream of the initiation codon. The duplicated region contains consensus sequences of binding sites for several known transcription factors, suggesting that different alleles may differ in their transcriptional activity. Because chimpanzees, gorillas, and orangutans lack the duplication, the duplicated allele is inferred to be derived. The frequency of this derived duplication allele ranges from 0.40-0.81 in the 11 populations from around the world typed for this polymorphism. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:705-709, 1999.

Alleles↗
PubMed1999

An interlaboratory study to determine the presence of human papillomavirus DNA in esophageal carcinoma from China.

Esophageal-carcinoma samples originating from the high-incidence area of China were tested in 2 different laboratories, each using a different degenerate PCR approach. Results confirmed the notion that none of the PCR approaches available for HPV-DNA detection today, is optimal for detecting all known HPV types at equal sensitivity and specificity. In combining results obtained in both laboratories, HPV DNA was demonstrated in 20/117 (17.1%) esophageal-carcinoma samples analyzed. HPV DNA was detected in 3/70 (4.3%) diagnostic biopsies, 7/23 (30.4%) surgical specimen and 10/24 (41.6%) cytological scrapings originating from the entire surface of the esophagus. Mucosotropic HPV types were present in 7/117 (6%) samples, only 3 being of the high-risk types (HPV 16, 18, 33). Other mucosal types found were HPV 6, 11, 13, 53 and 54. Cutaneous HPV types were present in 14/117 (12.0%) samples. HPVs 20 and 38 were present in 3 (2.6%) of the total samples and, in each case, together with another HPV type within one lesion. Two putative new HPV types, DL347 and DL 369, were identified.

Adult↗
PubMed1999

NHS-MAS3: a bifunctional chelator alternative to NHS-MAG3.

This laboratory uses an N-hydroxysuccinimide derivative of S-acetylmercaptoacetyltriglycine (NHS-MAG3) to conjugate amines for subsequent labeling with 99mTc. However, the synthesis from triglycerine is general and not restricted to this tripeptide. We had earlier selected a small number of alternative tripeptides and synthesized the corresponding NHS derivatives. Each was then evaluated in a search for bifunctional chelators with properties superior to NHS-MAG3, such as lower serum protein binding or improved stability to cysteine challenge. Based on these preliminary results, NHS-S-acetylmercaptoacetyltriserine (NHS-MAS3) was selected for further investigation. We have now conjugated this bifunctional chelator to an biocytin and to an amine-derivatized peptide nucleic acid (PNA). Both carriers were also conjugated with NHS-MAG3 under identical conditions and all were labeled with 99mTc at neutral pH and at boiling temperature while the conjugated PNAs were radiolabelled at neutral pH and at room temperature. Regardless of the chelator, reverse phase HPLC radiochromatograms of the labeled biotins and PNAs after purification showed a single peak. However, by size exclusion HPLC, the radiochromatograms always showed several peaks even after purification, but the MAS3 radiochromatograms were less complicated. For biotin and PNA both, radiolabeling via MAS3 showed improved 99mTc stability in 37 degrees C serum and in cysteine solution. The four preparations were administered to mice implanted in one thigh with avidin beads (biotins) or complementary PNA beads (PNAs). At 5 h post-administration, no significant differences were observed in the targeting of PNA beads between the two chelators, however the target thigh/normal thigh ratio was significantly higher for MAS3-biotin compared to MAG3-biotin. We conclude that labeling biocytin and amine-derivatized PNA with NHS-MAS3 compared to NHS-MAG3 provides simpler radiochromatographic profiles, improved stability of the label in serum and cysteine solution and can improve in vivo targeting.

Animals↗
PubMed1999

Technetium-99m labeled peptides--an investigation of multiple HPLC peaks.

This laboratory, and others, have reported multiple radioactive peaks in the size exclusion high performance liquid chromatographic (HPLC) analysis of 99mTc-labeled peptides. In the case of one 99mTc-MAG3-labeled peptide studied in this laboratory, human neutrophil elastase inhibitor, all five radioactive peaks were shown to be due to active peptide rather than radiocontaminants. By a variety of experiments, the nature of these peaks have now been examined. A high molecular weight UV peak could be generated by heating the MAG3 coupled, but not the native, peptide. Furthermore, this UV peak did not appear upon heating the peptide if the sulfur within the MAG3 chelator was replaced with oxygen. This peak may therefore be due to polymers resulting from intermolecular disulfide bond formation between sulfurs in the MAG3 chelate and the peptide. Several peaks with apparent lower molecular weights were absent on analysis with a different size exclusion column with superior resolution in their molecular weight range. More importantly, they were also absent on analysis by SDS polyacrylamide gel electrophoresis. These "low" molecular weight radioactive peaks may therefore be due to interactions between the 99mTc-MAG3 chelate and the peptide which produce multiple molecular configurations of identical molecular weight but differing in shape, charge, isomerism or lipophilicity such that they are resolved under the conditions of certain analyses. In support of this possibility, lengthening the linker between MAG3 and the peptide reduced the number of radioactive peaks, while encouraging the interaction by replacing MAG3 with the shorter MAG2 seemed to increase the number of radioactive peaks. Finally, that the three "low" molecular weight radioactive peaks reappeared when a single peak fraction was reanalyzed suggests that the species responsible are in rapid equilibrium. One conclusion from this investigation is that the appearance of a single peak by any HPLC analysis offers no assurance that multiple peaks would not appear on alternative HPLC analyses. Evidence that each species is due to radiolabeled active peptide and not to radiocontaminants is therefore potentially more important than evidence of a single peak.

Chelating Agents↗