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C Chen

Publications and source records attributed to C Chen.

At least 1,135 records · Page 63Linked to original sources
PubMed1990

Interaction of RNA polymerase I transcription factors with a promoter in the nontranscribed spacer of rat ribosomal DNA.

The spacer promoter of the rat rDNA repeat consists of two functional domains: a core (proximal) element that is sufficient for transcription in vitro, and an upstream (distal) promoter element that increases the efficiency of transcription. Two of the transcription factors that interact with the 45S promoter also interact with the spacer promoter. Rat SL-1, is required for transcription of the spacer promoter by heterologous extracts, e.g. human, and rat SF-1 is required for efficient transcription in vitro. Order-of-addition experiments demonstrated that the preinitiation complex formed by these factors on the spacer promoter is not as stable as the complex formed on the 45S promoter. DNase 1 footprinting experiments demonstrated binding sites for rat SL-1 and SF-1 on the distal element of the spacer promoter. The topology of the domains of the spacer promoter may explain both the reduced stability of the preinitiation complex formed on that promoter and the lower efficiency of transcription of that promoter when compared to the 45S promoter.

Animals↗
PubMed1990

Sodium and calcium currents in action potentials of rat somatotrophs: their possible functions in growth hormone secretion.

We report that both Na+ and Ca2+ currents are involved in the action potentials and in the hormone release from rat somatotrophs in primary culture. Single somatotrophs were identified by reverse hemolytic plaque assay (RHPA) and transmembrane voltage and currents were recorded using the whole-cell mode of the patch-clamp technique. Somatotrophs displayed a mean resting potential of -80mV and an average input resistance of 5.7G omega. Most of the cells showed spontaneous or evoked action potentials. Single action potentials or the initial spike in a burst were characterized by their high amplitude and short duration. Tetrodotoxin (TTX, 1 microM) blocked single action potentials and the initial spikes in a burst, whereas action potentials of long duration and low amplitude persisted. Cobalt (2 mM) plus TTX (1 microM) blocked all the action potentials. Voltage-clamp experiments confirmed the presence of both a TTX-sensitive Na+ current and Co2(+)-sensitive Ca2+ currents. TTX or Na(+)-free medium slightly decreased the basal release of GH but did not markedly modify hGRF-stimulated GH release. However, Co2+ (2 mM), which partially decreased the basal release, totally blocked hGRF-stimulated release. We conclude that (1) Na+ currents which initiate rapid action potentials may participate in spontaneous GH release; (2) Ca2+ currents, which give rise to long duration action potentials and membrane voltage fluctuation, are probably involved in both basal and hGRF-stimulated GH releases.

Action Potentials↗
PubMed1990

Development of an automated procedure for fluorescent DNA sequencing.

We describe here the development of a procedure for complete automation of the dideoxynucleotide DNA sequencing chemistry using fluorescent dye-labeled oligonucleotide primers. This procedure combines rapid preparation of template DNA using a modification of the polymerase chain reaction, automation of the DNA sequencing reactions using a robotic laboratory workstation, and subsequent analysis of the fluorescent-labeled reaction products on a commercial automated fluorescent sequencer. Using this procedure, we were able to produce sufficient quantities of template DNA directly from bacterial colonies or bacteriophage plaques, perform the DNA sequencing reactions on these templates, and load the reaction products on the fluorescent DNA sequencer in a single work day. This scheme for automation of the fluorescent DNA sequencing method allows the fluorescent sequencer to be run at its full capacity every day and eliminates much of the labor required to obtain a high level of data output. Currently, we are able to perform and analyze 16 fluorescent-labeled reactions every day, with an average output of over 7000 bp per sequencer run.

Automation↗
PubMed1990

Meat mutagens.

Explore the source record for details and available documents.

Animals↗
PubMed1990

Systemic to pulmonary venous shunting in superior vena cava obstruction. Unusual myocardial and thyroid visualization.

Obstruction of the superior vena cava is commonly associated with the development of several collateral venous pathways. Right-to-left systemic to pulmonary venous shunting, however, rarely has been reported. This paper describes a case in which a previously unsuspected shunt, manifested by the striking visualization of myocardial and thyroid tissue in addition to other findings, was discovered on a routine lung perfusion scan. Imaging, as well as radiologic studies are presented in the investigation of this phenomenon.

Adult↗
PubMed1990

Correction of extracapsular temporomandibular joint ankylosis with a cervical subcutaneous pedicle flap.

A new method of correcting extracapsular temporomandibular joint ankylosis with a cervical subcutaneous pedicle flap is described. In this procedure, a cervical subcutaneous pedicle flap with or without platysma is introduced into the oral cavity through a tunnel to repair the defect after the buccal scar is excised and the normal oral opening is restored. Sixteen consecutive patients underwent the surgery, and good results were obtained.

Adolescent↗
PubMed1990

Reconstruction of the concha of the ear using a postauricular island flap.

An effective method of reconstruction of the auricular conchal cavity using a postauricular island flap containing the postauricular blood vessels is described. In this procedure, the island flap is brought in to cover the defect of the conchal cavity through a tunnel between the defect and the retroauricle. Sound anatomic and mechanical principles are introduced in this technique. Two patients underwent the operation, and good results were obtained.

Adult↗
PubMed1990

Improved technique for a one-stage repair of significant defects of the ear.

An improved technique for repair of severe acquired partial defects of the auricle in one stage is described. The common postauricular flap with its base on the margin of the auricular defect is usually unable to repair a severe partial auricular defect in one stage because of the limited length of the flap. The authors developed this technique by means of lengthening the flap with a piece of subcutaneous tissue of the scalp, so that the ear framework can be covered completely in one stage. All flaps in this group survived totally. Seven patients with severe acquired partial defects of the auricle underwent this procedure, and good results were obtained.

Adult↗
PubMed1990

Two types of voltage-dependent calcium current in rat somatotrophs are reduced by somatostatin.

1. Somatotrophs were obtained from rat pituitary glands after dissociation, separation and enrichment on a continuous gradient of bovine serum albumin at unit gravity. Somatotrophs were enriched up to 85% in the heavy fractions (F8 and F9). 2. After identification by reverse hemolytic plaque assay, patch-clamp recording in the whole-cell mode was performed on somatotrophs. 3. Under voltage-clamp conditions, two types of Ca2+ currents were recorded. From a holding potential of -70 mV, depolarizing voltage steps to potentials more positive than -50 mV activated a current which rapidly inactivated and which was very sensitive to Ni2+ but not to Cd2+. This current corresponds to T-type current. Depolarizing steps to potentials more positive than -30 mV from a holding potential of -40 mV triggered a current which slowly inactivated and which was very sensitive to Cd2+ but not to Ni2+. This current corresponds to L-type current. 4. Application of somatostatin to the bath solution (10 nM) markedly reduced the amplitudes of both T- and L-type currents. Somatostatin decreased the conductance of L-type current without modifying its time- and voltage-dependent inactivation but its activation was not affected. However, somatostatin decreased the conductance of T-type currents, and also accelerated its time-dependent inactivation. Half-inactivation voltage of T-type current was shifted from -52 to -63 mV by somatostatin but no change was obtained in the current activation curve. 5. All these modifications in Ca2+ currents were abolished by a pre-treatment of the cultures with pertussis toxin (100 ng/ml, for 10 h). This pre-treatment also blocked the inhibitory effect of somatostatin on high-K(+)-stimulated growth hormone release. 6. Our results show that somatostatin acts on somatotrophs by attenuating the voltage-dependent Ca2+ currents. These effects may contribute to a somatostatin-induced reduction in [Ca2+]i and the subsequent decline in growth hormone release.

Animals↗
PubMed1990

Coregulation of type 12 M protein and streptococcal C5a peptidase genes in group A streptococci: evidence for a virulence regulon controlled by the virR locus.

Group A streptococci express at least two surface-associated virulence factors, the antiphagocytic M protein and the antichemotactic streptococcal C5a peptidase (SCP). Preliminary evidence suggested that the biosynthesis of these two proteins is coordinately controlled and subject to simultaneous phase variation. To explore this possibility further, a series of phase-switching and phase-locked M- variants were assayed for SCP by enzyme-linked immunosorbent assay inhibition and for SCP-specific mRNA by dot blot hybridization. All M- cultures produced diminished amounts of SCP antigen and specific mRNA, whereas revertants produced quantities equivalent to those of the wild-type M+ culture. A phase-locked strain that harbors a deletion in a region upstream of the M12 and SCP genes, termed the virR locus, failed to produce SCP antigen or SCP-specific transcripts. The SCP-specific transcript produced by M+ bacteria was shown by Northern (RNA) blot hybridization to be 4 kilobases in size, distinguishing it from the transcript which encodes M protein. These data demonstrate that phase switching of both SCP and M12 proteins is at the transcriptional level and that expression is under the control of the upstream virR locus. We propose that the genetic determinants of these proteins and of colony morphology comprise a virulence regulon.

Adhesins, Bacterial↗