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Biomedical subjects

K Yang

Publications and source records attributed to K Yang.

At least 235 records · Page 13Linked to original sources
PubMed1995

Regulation of jadomycin B production in Streptomyces venezuelae ISP5230: involvement of a repressor gene, jadR2.

The nucleotide sequence of a region upstream of the type II polyketide synthase genes in the cluster for biosynthesis of the polyketide antibiotic jadomycin B in Streptomyces venezuelae contained an open reading frame encoding a sequence of 196 amino acids that resembeled sequences deduced for a group of repressor proteins. The strongest similarity was to EnvR of Escherichia coli, but the sequence also resembled MtrR, AcrR, TetC, and TcmR, all of which are involved in regulating resistance to antibiotics or toxic hydrophobic substances in the environment. Disruption of the nucleotide sequence of this putative S. venezuelae repressor gene (jadR2), by insertion of an apramycin resistance gene at an internal MluI site, and replacement of the chromosomal gene generated mutants that produced jadomycin B without the stress treatments (exposure to heat shock or to toxic concentrations of ethanol) required for jadomycin B production by the wild type. When cultures of the disruption mutants were ethanol stressed, they overproduced the antibiotic. From these results it was concluded that expression of the jadomycin B biosynthesis genes are negatively regulated by jadR2.

Amino Acid Sequence↗
PubMed1995

Expression of multiple isoenzymes of protein kinase C in airway smooth muscle.

Protein kinase C (PKC) has been implicated in the control of airway smooth muscle (ASM) tone, and abnormalities in PKC-dependent signaling may be associated with asthma. PKC exists in different isoforms, but the pattern of their expression in ASM has not been previously reported. Accordingly, the purpose of the present study was to identify which isoforms of PKC are expressed in ASM. Tissue samples of canine ASM were homogenized and subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis, followed by immunoblotting with a range of antipeptide antibodies to PKC-alpha, -beta I, -beta II, -gamma, -delta, -epsilon, -eta, -theta, and -zeta. Positive controls were run in parallel with ASM. Immunoblots revealed a mixture of both calcium-dependent and calcium-independent isozymes: PKC-beta I and PKC-beta II were the only conventional isoforms detected; PKC-delta, PKC-epsilon, and the new muscle-specific isoform, PKC-theta, were all expressed in ASM, but the lung-specific isoform, PKC-eta, was not detected. The calcium- and phospholipid-independent isoform, PKC-zeta, was also present. Thus, expression of a wide variety of both calcium-dependent and calcium-independent isoforms suggests a complex, multifunctional role of PKC in ASM.

Animals↗
PubMed1995

Developmental and glucocorticoid regulation of pituitary 11 beta-hydroxysteroid dehydrogenase 1 gene expression in the ovine fetus and lamb.

To examine the role of 11 beta-hydroxysteroid dehydrogenase 1 (11 beta-HSD1) in the control of glucocorticoid actions in the ovine pituitary during development, we have sought developmental changes in the distribution and the level of 11 beta-HSD1 mRNA by in situ hybridization. In the pars distalis, 11 beta-HSD1 mRNA was present by day 60; its amount did not change significantly until term (days 145-147) when it increased dramatically. The level of 11 beta-HSD1 mRNA increased further during the postnatal period. In contrast, 11 beta-HSD1 mRNA in the pars intermedia was not detectable until day 135; it increased in amount at days 140-143, but did not change significantly thereafter through to adulthood. We have also measured levels of both dehydrogenase and reductase activities of 11 beta-HSD1 in the pars distalis of fetal sheep at day 140 and term, and of postnatal sheep at 1-2 months of age, to determine whether changes in 11 beta-HSD1 mRNA are reflected in the levels of enzyme activities. There were progressive increases in both dehydrogenase and reductase activities from day 140 to 1-2 months postnatally, although dehydrogenase activity was consistently higher than reductase activity. Finally, we have determined the effect of short-term intrafetal cortisol infusion (5 micrograms/min for 12 h) on levels of pituitary 11 beta-HSD1 mRNA by in situ hybridization. There was no effect of cortisol infusion on 11 beta-HSD1 mRNA expression.(ABSTRACT TRUNCATED AT 250 WORDS)

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1995

Expression, distribution, regulation and function of IGFs in the ovine fetal pituitary.

Activation of the fetal pituitary-adrenal axis is crucial for fetal organ maturation and the onset of parturition in sheep. Many factors including corticotrophin-releasing hormone (CRH) and arginine vasopressin secreted from the hypothalamus, and growth factors produced within the pituitary may be involved in the regulation of maturation of the fetal pituitary gland. IGFs have mitogenic and differentiation-promoting capacities in a variety of organs and are synthesized as paracrine factors within developing tissues. However, there is little information concerning the synthesis, distribution, regulation and function of IGFs in the fetal pituitary gland at different times during pregnancy. Therefore, we have localized IGF-I and IGF-II mRNAs and peptides, and determined the effect of cortisol on the level of IGF-II mRNAs in the pituitary glands of developing sheep fetuses. We examined the possible effects of IGFs on corticotroph function in cultures of adenohypophysial cells from term fetuses. Seven species of IGF-II transcripts of 1.2-6.0 kb were identified by Northern blot analysis in the pituitary gland of fetuses between day 60 of gestation and term (day 145). The levels of IGF-II mRNAs did not change significantly during pregnancy, although there was a trend for the presence of higher levels of IGF-II mRNAs at day 60 of gestation. IGF-I mRNA was not detectable. By in situ hybridization, IGF-II mRNA was localized to non-endocrine cells and to cells lining the blood vessels of the pars distalis, to some presumed endocrine cells in the pars distalis and pars intermedia, and to clusters of cells in the pars nervosa. In contrast, IGF-I and IGF-II peptides were detected in the presumed endocrine cells in the pars distalis and pars intermedia but not in the pars nervosa. Incubation of adenohypophysial cells from term fetuses with IGF-I, but not IGF-II, for 48 h increased specific 125I-Tyr-ovine CRH binding. However, neither IGF-I nor IGF-II had any significant effects on the basal or CRH-stimulated immunoreactive (ir)-ACTH output, the level of POMC mRNA or the number of ir-ACTH positive cells. Infusion of cortisol to fetuses starting at day 96 of gestation for 100 h or at days 120-125 of gestation for 84 h did not affect the level of IGF-II mRNAs in the pars distalis but decreased the levels of POMC mRNA. These results are consistent with IGFs having the potential to influence fetal pituitary function, although probably on cell types other than the corticotrophs.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropic Hormone↗
PubMed1995

Changes in glucocorticoid receptor mRNA in the developing ovine pituitary and the effects of exogenous cortisol.

Developmental changes in pituitary glucocorticoid receptor (GR) mRNA were examined during gestation and early neonatal life using in situ hybridization. Pituitaries were harvested from sheep fetuses at days 60-80, 100-120, 130-135, 140-142 and term, and from lambs of days 0-7 and 30-60, and adults. GR mRNA was present in the pars distalis by day 60, levels increased through gestation, and there was a redistribution of GR mRNA, resulting in a relatively greater abundance at the base of the pars distalis. At term, there was a significant (P < 0.05 compared with the day 140-142 fetuses) elevation of GR mRNA, which was maintained in the newborn lamb, reaching highest levels at days 30-60 of neonatal life. GR mRNA was undetectable in the pars intermedia until day 120, but subsequently increased to high levels at term. Interestingly, the expression of GR mRNA in the pars intermedia dropped precipitously in the newborn (P < 0.05 compared with term), though levels recovered in the older lambs and adults. The regional and cellular distribution of GR mRNA correlated closely with the presence of immunoreactive GR (irGR) in the pituitary; the majority of irGR was present in the nuclei. Intrafetal infusion of cortisol (12 h; 5 micrograms/min) in late gestation (day 135) had no effect on Gr mRNA expression in either the pars distalis or pars intermedia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Corticosteroid-binding globulin (CBG) production by hepatic and extra-hepatic sites in the ovine fetus; effects of CBG on glucocorticoid negative feedback on pituitary cells in vitro.

Plasma cortisol levels increase in fetal sheep during late gestation and this is associated with an increase in plasma corticosteroid-binding globulin (CBG) concentrations. However, the relative tissue sources of plasma CBG, the ontogeny of its biosynthesis and glycoform composition have not been established in the ovine fetus. Therefore we examined whether changes in plasma corticosteroid binding capacity (CBC) in fetal sheep during late gestation were associated with different patterns of glycosylation and reflected changes in tissue CBG expression. Since free cortisol is considered the bioactive fraction, we measured changes in the percent and absolute free cortisol in fetal plasma during late gestation. In order to examine whether CBG alters cortisol negative feedback at the level of the fetal pituitary, we also examined the effect of exogenous CBG in mediating the glucocorticoid-induced suppression of basal and corticotrophin-releasing hormone (CRH)-stimulated ACTH release from fetal pituitary cells in culture. The mean free cortisol concentration in plasma was not different between days 15 and 20 prior to parturition, and between 5 and 10 days prepartum, although it did rise between these times. Plasma CBC in chronically catheterized fetuses rose from 23.3 +/- 4.6 ng/ml at day 115 to 86.5 +/- 20.8 ng/ml at term and then decreased rapidly after birth. Between day 125 and day 140 of pregnancy approximately 10% of fetal plasma CBG was retarded by Concanavalin-A chromatography. This proportion increased at birth and attained adult values of > 70% by one month of age. By Northern blotting the relative levels of CBG mRNA in the fetal liver did not change between days 100 and 125, then increased significantly at day 140, but declined at term and in newborn lambs. CBG mRNA was undetectable in total RNA from lung, kidney, hypothalamus and placentomes, but was present in the fetal pituitary at days 125 and 140. Reverse transcription-PCR was used to confirm the presence of CBG mRNA in pituitary tissue from term fetuses. In cultures of term fetal pituitary cells, added CBG attenuated the cortisol- but not the dexamethasone-mediated suppression of basal and CRH-stimulated ACTH release. We conclude that in fetal sheep there is an increase in the corticosteroid binding capacity of plasma during late pregnancy which regulates, in part, free cortisol levels in the circulation. The liver is the major site of CBG biosynthesis in the fetus and at least until day 140 of gestation the rise in plasma CBC is associated with an increase in hepatic CBG mRNA levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropic Hormone↗
PubMed1995

Differential expression of 11 beta-hydroxysteroid dehydrogenase 1 and 2 in the developing ovine fetal liver and kidney.

In adult mammals, liver and kidney are the two major sites of biosynthesis for 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) 1 and 2 respectively. In the present study, the expression of these two isozymes in the developing ovine fetal liver and kidney was characterized. Livers and kidneys were obtained from fetal sheep at days 85, 100-120 and 140-143 of gestation (term = 145 days). Tissue levels of 11 beta-HSD2 mRNA were assessed by Northern blot analysis. 11 beta-HSD dehydrogenase and reductase activities in tissue homogenates were determined by a radiometric conversion assay using cortisol and cortisone as physiological substrates respectively. The unidirectional 11 beta-HSD2 dehydrogenase activity was identified by its distinct cofactor preference (NAD), and by its unique ability to metabolize dexamethasone (Dex). In the liver, 11 beta-HSD1 dehydrogenase and reductase activities were present by day 85, and their levels did not change between days 85 and 100-120 but increased more than twofold at days 140-143. This was consistent with changes we reported previously in the fetal hepatic 11 beta-HSD1 mRNA. 11 beta-HSD1 reductase activity was always higher than the dehydrogenase activity. 11 beta-HSD2 mRNA and activity were undetectable in the fetal liver at all three ages. By contrast, 11 beta-HSD2 mRNA was present in the fetal kidney by day 85, and its abundance increased progressively thereafter. There was a parallel increase in the renal 11 beta-HSD2 activity. Dex was also converted to 11-dehydro-Dex by the fetal kidney. In keeping with the absence of the full-length 11 beta-HSD1 mRNA, 11 beta-HSD1 activity was undetectable in the kidney. These results indicate that (1) 11 beta-HSD1 and 2 genes are differentially expressed and regulated in the fetal liver and kidney during development, (2) since the hepatic 11 beta-HSD1 reductase activity is always higher than the dehydrogenase activity, the fetal liver may be a potential extra-adrenal source of cortisol, and (3) 11 beta-HSD2 in the kidney may play a very important role in protecting the fetus from elevated levels of bioactive glucocorticoids.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1995

International study of expert judgment on therapeutic use of benzodiazepines and other psychotherapeutic medications: III. Clinical features affecting experts' therapeutic recommendations in anxiety disorders.

Our objective was to assemble expert clinical experience and judgment in the treatment of anxiety and related disorders in a systematic, quantitative manner. This article reports on some clinical features apart from diagnosis that may affect choice of strategy in the pharmacotherapy of anxiety disorders. A panel of internationally recognized experts in treating anxiety and depression was constituted by multistage peer nomination. Ninety percent (66 of 73) completed an extensive questionnaire. This report focuses on the expert panel's responses to questions on therapeutic options, based on multi-part case vignettes of several anxiety disorders presenting clinical variations within the same diagnosis. In the presence of higher levels of functional impairment, the experts more often recommended formal psychosocial procedures for adjustment disorder; medication for agoraphobia, social phobia, obsessive-compulsive disorder, and adjustment disorder; and polypharmacy for agoraphobia. Their therapeutic recommendations were not materially affected by chronicity in the case of panic disorder. Under the condition of heavy use of alcohol in the case of generalized anxiety disorder, the experts avoided benzodiazepines in favor of various other medications. In the presence of a serious cardiac conduction defect in the case of obsessive-compulsive disorder, they less often recommended medication. Those who did recommend medication changed their preference from tricyclic antidepressants (clomipramine) to selective serotonin reuptake inhibitors. Under the condition of a more severe precipitating event in the case of adjustment disorder, the experts were more likely to recommend both formal psychosocial intervention and medication.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

[Successful replantation in ten-digit complete amputation: a case report].

We report a case of successful replantation of ten-digit complete amputation. The conditions of the wounds over the ends of the ten amputated digits varied from severe to light and easy for replantation. The amputation included severe avulsion injuries over four fingers. Appropriate measures were taken during surgery and the replanted digits all survived. The replantation operation was done by a team of surgeons. Although the surgeons were physically challenged by the long and difficult procedures, they worked hard for the benefit of the patient. Physiotherapy and exercises six months after operation showed that the functions of both hands were largely recovered.

Adult↗
PubMed1995

[Experimental research and clinical application of allogenic tendon grafting].

Autologous free tendon grafting is a very common treatment for tendon defect of the hand. However, it is difficult to obtain autologous free tendon grafts to repair patients with multiple tendon defects. We described the treatment using deep-freeze-stored tendon with MEM and the establishment of clinical tendon bank. Allograft tendons were used successfully in 15 patients clinically. In the experiments, we also performed a series of studies on immunity and repairing ability of the allogenic tendon grafts. The results indcated that the treatmnet using deep-freeze-stored tendon with MEM could reduce the immunogenicity of allograft. There was no significant difference between autograft and deep-freeze stored allograft 24 weeks after operation, but there was a significant difference in the fresh allograft 3 weeks after grafting. Based on animal experiment, we established a clinical tendon bank. Deep-freeze-stored allogenic tendon grafts can be used successfully in place of autologous tenden grafts in treatment of tendon defect of the hand.

Animals↗
PubMed1995

Integration of glucoamylase gene from Aspergillus niger into Saccharomyces cerevisiae genome and its stable expression.

Starch digestible delta-integrants were constructed by integrative transformation of a linear YIP plasmid carrying Aspergillus niger glucoamylase cDNA under the control of the MF alpha 1 promoter and its prepro signal and the delta sequence of the Ty element from yeast. The integration of glucoamylase cDNA into Saccharomyces cerevisiae was identified by Southern analysis. The secreted glucoamylase activity of integrants in the medium with soluble starch as a carbon source reached 2.5 u/ml. After ten times of successive transfers in a nonselective medium, the activity of secreted glucoamylase of integrant was approximately at its original level.

Aspergillus niger↗
PubMed1994

Optimizing liposome-mediated gene transfer in primary rat septo-hippocampal cell cultures.

Although liposomes have been widely employed to transfect DNA into a variety of cell types, no previous studies have systematically examined conditions producing optimal liposomal-mediated transfection of DNA into central nervous system (CNS) cells. Thus, we used the beta-galactosidase (beta-gal) reporter gene to examine factors influencing the efficiency of liposome-mediated gene transfection in CNS cell cultures. Our results indicate that without increasing the amounts of DNA, increased liposome concentrations within certain limits enhanced transfection efficiency. However, higher liposome levels could produce cell lysis. Without increasing liposome concentrations, increased amounts of DNA did not improve transfection efficiency. Employing the optimal concentration (1 microgram DNA/3 microliters liposomes/well), beta-gal gene expression was sustained for at least two weeks after transfection in primary septo-hippocampal cultures.

Animals↗
PubMed1994

Sustained expression of functional nerve growth factor in primary septo-hippocampal cell cultures by liposome-mediated gene transfer.

We examined liposome-mediated gene transfection of nerve growth factor (NGF) in primary central nervous system cultures. RT-PCR analyses detected increased expression of NGF mRNA one day after liposome-mediated NGF gene transfection. ELISA studies detected large increases in NGF protein in cells and in culture medium after NGF gene transfection. Cells continued to secrete NGF into the medium for at least 2 weeks. NGF bioassays confirmed that the NGF secreted after gene transfection was biologically active.

Animals↗
PubMed1994

Increased expression of c-fos mRNA and AP-1 transcription factors after cortical impact injury in rats.

Levels of c-fos mRNA and AP-1 transcription factors co-expression were measured in a controlled lateral cortical impact model of traumatic brain injury (TBI) in rats. Ipsilateral cerebral cortex and bilateral hippocampal c-fos mRNA increases were revealed by in situ hybridization after lateral cortical impact injury. Based on regional in situ hybridization data, we employed semi-quantitative RT-PCR methods to study the temporal profile of changes in the ipsilateral cortex at the site of injury. We found that TBI produces transient increases of c-fos mRNA expression in the ipsilateral cerebral cortex at 5 min postinjury, which peaks at 1 h postinjury and subsides by 1 day postinjury. Gel shift nuclear protein binding assays showed that AP-1 transcription factor binding was robustly increased in injured cerebral cortex at 1 h, 3 h, 5 h and 1 day after injury. These data indicate that TBI can produce significant increases in c-fos expression and subsequent upregulation of the AP-1 transcription factors. Thus, AP-1 transcription factors modulation of downstream gene expression may be an important component of pathophysiological responses to TBI.

Animals↗
PubMed1994

A targeted chain-termination mutation in the mouse Apc gene results in multiple intestinal tumors.

Germ-line mutations in the human adenomatous polyposis coli (APC) gene result in familial adenomatous polyposis, an autosomal dominant disorder characterized by the early onset of multiple adenomatous polyps in the large bowel with a high likelihood of developing colorectal carcinomas. To understand the role of APC in intestinal tumor formation, we have introduced a chain-termination mutation in the 15th exon of the mouse Apc gene and employed it to modify the endogenous gene by homologous recombination in embryonic stem cells. Mice which are heterozygous for the Apc gene modification progressively develop intestinal tumors in a manner that is similar to that observed in patients with familial adenomatous polyposis and in mice which carry a mutation called multiple intestinal neoplasia (Min). Our results indicate that the Apc gene modification is a critical event in the initiation of intestinal tumor formation and results in an autosomal dominant predisposition toward development of spontaneous colonic and intestinal tumors in mice.

Adenomatous Polyposis Coli↗
PubMed1994

Assisted refolding of recombinant prochymosin with the aid of protein disulphide isomerase.

Protein disulphide isomerase (PDI) was shown to be able to accelerate the refolding of unfolded recombinant prochymosin and to enhance the overall yield of active protein. Unlike previous reports in this study PDI was found to be active at pH values as high as 11. The coincidence of the similar apparent optimum pH values of uncatalysed and PDI-catalysed reactions suggests that conditions favourable to spontaneous refolding of proteins may help PDI to catalyse thiol/disulphide interchange. Under the conditions described here no exogenously added dithiothreitol was required for PDI-catalysed renaturation, implying that the disulphide form of PDI was reduced to its active form by the free thiol groups in prochymosin molecules.

Animals↗