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C Y Lai

Publications and source records attributed to C Y Lai.

At least 37 records · Page 2Linked to original sources
PubMed1999

The fas and fas ligand pathways in liver allograft tolerance.

The Fas and Fas ligand (Fas/FasL) pathways may play a central role in cytotoxicity or immunoregulation in liver transplantation. Here, in an attempt to examine the role of Fas/FasL on drug-free tolerance, we measured mRNA levels of Fas/FasL in livers by reverse transcriptase-polymerase chain reaction (RT-PCR), and also protein levels of Fas/FasL in livers by immunohistochemistry and in serum by dot blot assay. PVG recipients bearing DA livers showed serious rejection between post-operative (POD) days 7 and 14, but this rejection was naturally overcome without any immunosuppression. Fas gene and protein products were expressed on almost every cell in livers taken from naive rats, and at any time point in both syngeneic and allogeneic orthotopic liver transplantation (OLT) rats. In contrast, FasL mRNA in DA livers was detectable at POD 2, peaked at POD 14, and declined at POD 63 in allogeneic OLT (DA-PVG). Although the FasL gene was detectable in isografts at POD 14, its expression was much lower than in allografts. The time course and localization of FasL expression indicated that the expression of FasL gradually switched from infiltrating cells to hepatocytes when the rejection was naturally overcome and tolerance was induced in this OLT model. Soluble Fas could constitutively be detected at any time point in the serum of the tolerogenic OLT (DA-PVG) rats and was not diminished during the rejection phase. Soluble FasL peaked at POD 14 in allogeneic OLT, while sFasL was significantly lower in the serum of normal and syngeneic OLT rats. These findings suggest that the Fas and FasL pathways, including soluble forms, may contribute to the control of the immune response in this drug-free tolerance OLT model.

Animals↗
PubMed1999

Modulation of life-span by histone deacetylase genes in Saccharomyces cerevisiae.

The yeast Saccharomyces cerevisiae has a limited life-span, which is measured by the number of divisions that individual cells complete. Among the many changes that occur as yeasts age are alterations in chromatin-dependent transcriptional silencing. We have genetically manipulated histone deacetylases to modify chromatin, and we have examined the effect on yeast longevity. Deletion of the histone deacetylase gene RPD3 extended life-span. Its effects on chromatin functional state were evidenced by enhanced silencing at the three known heterochromatic regions of the genome, the silent mating type (HM), subtelomeric, and rDNA loci, which occurred even in the absence of SIR3. Similarly, the effect of the rpd3Delta on life-span did not depend on an intact Sir silencing complex. In fact, deletion of SIR3 itself had little effect on life-span, although it markedly accelerated the increase in cell generation time that is observed during yeast aging. Deletion of HDA1, another histone deacetylase gene, did not result in life-span extension, unless it was combined with deletion of SIR3. The hda1Delta sir3Delta resulted in an increase in silencing, but only at the rDNA locus. Deletion of RPD3 suppressed the loss of silencing in rDNA in a sir2 mutant; however, the silencing did not reach the level found in the rpd3Delta single mutant, and RPD3 deletion did not overcome the life-span shortening seen in the sir2 mutant. Deletion of both RPD3 and HDA1 caused a decrease in life-span, which resulted from a substantial increase in initial mortality of the population. The expression of both of these genes declines with age, providing one possible explanation for the increase in mortality during the life-span. Our results are consistent with the loss of rDNA silencing leading to aging in yeast. The functions of RPD3 and HDA1 do not overlap entirely. RPD3 exerts its effect on chromatin at additional sites in the genome, raising the possibility that events at loci other than rDNA play a role in the aging process.

Aging↗
PubMed1999

Interorganelle signaling is a determinant of longevity in Saccharomyces cerevisiae.

Replicative capacity, which is the number of times an individual cell divides, is the measure of longevity in the yeast Saccharomyces cerevisiae. In this study, a process that involves signaling from the mitochondrion to the nucleus, called retrograde regulation, is shown to determine yeast longevity, and its induction resulted in postponed senescence. Activation of retrograde regulation, by genetic and environmental means, correlated with increased replicative capacity in four different S. cerevisiae strains. Deletion of a gene required for the retrograde response, RTG2, eliminated the increased replicative capacity. RAS2, a gene previously shown to influence longevity in yeast, interacts with retrograde regulation in setting yeast longevity. The molecular mechanism of aging elucidated here parallels the results of genetic studies of aging in nematodes and fruit flies, as well as the caloric restriction paradigm in mammals, and it underscores the importance of metabolic regulation in aging, suggesting a general applicability.

Antifungal Agents↗
PubMed1998

Heat stress-induced life span extension in yeast.

The yeast Saccharomyces cerevisiae has a limited life span that can be measured by the number of times individual cells divide. Several genetic manipulations have been shown to prolong the yeast life span. However, environmental effects that extend longevity have been largely ignored. We have found that mild, nonlethal heat stress extended yeast life span when it was administered transiently early in life. The increased longevity was due to a reduction in the mortality rate that persisted over many cell divisions (generations) but was not permanent. The genes RAS1 and RAS2 were necessary to observe this effect of heat stress. The RAS2 gene is consistently required for maintenance of life span when heat stress is chronic or in its extension when heat stress is transient or absent altogether. RAS1, on the other hand, appears to have a role in signaling life extension induced by transient, mild heat stress, which is distinct from its life-span-curtailing effect in the absence of stress and its lack of involvement in the response to chronic heat stress. This distinction between the RAS genes may be partially related to their different effects on growth-promoting genes and stress-responsive genes. The ras2 mutation clearly hindered resumption of growth and recovery from stress, while the ras1 mutation did not. The HSP104 gene, which is largely responsible for induced thermotolerance in yeast, was necessary for life extension induced by transient heat stress. An interaction between mitochondrial petite mutations and heat stress was found, suggesting that mitochondria may be necessary for life extension by transient heat stress. The results raise the possibility that the RAS genes and mitochondria may play a role in the epigenetic inheritance of reduced mortality rate afforded by transient, mild heat stress.

Blotting, Northern↗
PubMed1998

Prothymosin alpha modulates the interaction of histone H1 with chromatin.

Prothymosin alpha (ProTalpha) is an abundant acidic nuclear protein that may be involved in cell proliferation. In our search for its cellular partners, we have recently found that ProTalpha binds to linker histone H1. We now provide further evidence for the physiological relevance of this interaction by immunoisolation of a histone H1-ProTalpha complex from NIH 3T3 cell extracts. A detailed analysis of the interaction between the two proteins suggests contacts between the acidic region of ProTalpha and histone H1. In the context of a physiological chromatin reconstitution reaction, the presence of ProTalpha does not affect incorporation of an amount of histone H1 sufficient to increase the nucleosome repeat length by 20 bp, but prevents association of all further H1. Consistent with this finding, a fraction of histone H1 is released when H1-containing chromatin is challenged with ProTalpha. These results imply at least two different interaction modes of H1 with chromatin, which can be distinguished by their sensitivity to ProTalpha. The properties of ProTalpha suggest a role in fine tuning the stoichiometry and/or mode of interaction of H1 with chromatin.

3T3 Cells↗
PubMed1998

Epigenetic stratification: the role of individual change in the biological aging process.

Aging is a complex process. It consists of a diverse assortment of seemingly random manifestations that occur in the individual, the mutual relationship and impact on mortality of which is frequently obscure. We derive a simple equation to model the aging process based on scale invariant and increasing change. The solution to this equation indicates that this change itself, irrespective of its quality, is the cause and not simply the effect of aging. This model establishes loss of homeostasis as a fundamental feature of aging. The model is deterministic, but it supports the stochastic nature of age changes. Paradoxically, this model states that a sufficient augmentation of aging processes results in a lack of aging. Experimental evidence in support of this model is presented that spans the levels of population mortality rates, cellular spatial organization, and gene dysregulation.

Aging↗
PubMed1998

Development of respirable aerosol samplers using porous foams.

Workplace aerosols must be sampled to assess the degree of health hazard caused by the particulate matter. By adjusting the sampling flow rate, most of the samplers can match the 50% cutoff size, but not the slope of the respirable convention defined by the American Conference of Governmental Industrial Hygienists, the International Organization for Standardization, and the European Committee for Standardization (CEN). Combinations of foams (or other porous material) of different nominal sizes (10-100 ppi) and thicknesses (5-35 mm) were employed to overcome this bias. A foam disk 25 mm in diameter was placed in an asbestos sampling cowl. Dioctylphthalate was the liquid test agent. An aerodynamic particle sizer and an Aerosizer were calibrated against a settling chamber and were employed to measure the aerosol number concentrations and size distributions upstream and downstream of the foams. The sampling efficiency data showed that the 50% cutoff size could be met for foams in series, but that the slope remained sharper than the new definition. Foams in parallel showed great flexibility and many of the parallel combinations flattened the slope, closer to that of the new international respirable convention. For instance, when the total flow rate is set at 10.1 L/min the aerosol penetration through foams in parallel (100 ppi, 20 mm thick, diameter 25 mm + 10 ppi, 20 mm thick, diameter 13 mm) nearly matched the new international standard for respirable fraction. This sampler can be further miniaturized for smaller sampling flow rates to fit the capacity of personal sampling pumps.

Aerosols↗
PubMed1998

A methodological improvement and system validation to obtain precise behavioral parameters for schedule-induced polydipsia.

A Schedule-Induced Polydipsia (SIP) animal behaviors monitor system was devised. The system included a software package to acquire data and to format the data storage of the animal behavior in the experiment was designed. Data analysis software will also extract the necessary information from recorded data. The SIP experimental apparatus consists of a number of subsystems. They are operant chambers, event counters, signal acquisition and storage system. The operant chamber is equipped with hopper, pellet and lick sensor and locomotion detector. The data acquisition and storage subsystem are custom designed that run on IBM-PC. The discrete time markers for pellet drop, bar pressing and licking water were recorded at 200 Hz. The image of rat locomotion was recorded at 10 Hz. A test of four different stages of animal to verify the accuracy of the system was reported in this article. The food-deprived rats that were exposed to the intermittent food schedule (1 per minute) exhibit an excess drinking behavior. The animal behaviors that were monitored during the scheduled events are adjunctive, facultative and terminal behavior. The volume of water intake was also recorded for reference. The real time data is stored chronologically into two types of data file. Therefore, a special data analysis procedure is designed to extract the results for off-line statistic analysis. The extracted parameters for animal behaviors analyzing including drinking efficiency, inter-lick intervals, number of drinking bursts, size of burst, temporal distribution of licking, temporal distribution of bar pressing and locomotion. The system can be employed in many different SIP studies such as investigating the effect of acute and chronic influence of amphetamine.

Animals↗
PubMed1996

The tryptophan biosynthetic pathway of aphid endosymbionts (Buchnera): genetics and evolution of plasmid-associated anthranilate synthase (trpEG) within the aphididae.

The bacterial endosymbionts (Buchnera) from the aphids Rhopalosiphum padi, R. maidis, Schizaphis graminum, and Acyrthosiphon pisum contain the genes for anthranilate synthase (trpEG) on plasmids made up of one or more 3.6-kb units. Anthranilate synthase is the first as well as the rate-limiting enzyme in the tryptophan biosynthetic pathway. The amplification of trpEG on plasmids may result in an increase of enzyme protein and overproduction of this essential amino acid, which is required by the aphid host. The nucleotide sequence of trpEG from endosymbionts of different species of aphids is highly conserved, as is an approximately 500-bp upstream DNA segment which has the characteristics of an origin of replication. Phylogenetic analyses were performed using trpE and trpG from the endosymbionts of these four aphids as well as from the endosymbiont of Schlechtendalia chinensis, in which trpEG occurs on the chromosome. The resulting phylogeny was congruent with trees derived from sequences of two chromosome-located bacterial genes (part of trpB and 16S ribosomal DNA). In turn, trees obtained from plasmid-borne and bacterial chromosome-borne sequences were congruent with the tree resulting from phylogenetic analysis of three aphid mitochondrial regions (portions of the small and large ribosomal DNA subunits, as well as cytochrome oxidase II). Congruence of trees based on genes from host mitochondria and from bacteria adds to previous support for exclusively vertical transmission of the endosymbionts within aphid lineages. Congruence with trees based on plasmid-borne genes supports the origin of the plasmid-borne trpEG from the chromosomal genes of the same lineage and the absence of subsequent plasmid exchange among endosymbionts of different species of aphids.

Amino Acid Sequence↗
PubMed1996

The endosymbiont (Buchnera sp.) of the aphid Diuraphis noxia contains plasmids consisting of trpEG and tandem repeats of trpEG pseudogenes.

Most aphids are dependent for their survival on prokaryotic endosymbionts assigned to the genus Buchnera. Among the functions of Buchnera species is the synthesis of tryptophan, which is required by the aphid host. In Buchnera species from the aphid Diuraphis noxia, the genes for anthranilate synthase (trpEG) were found on a plasmid which consisted of seven tandem repeats of a 3.2-kb unit and one 2.6-kb unit which differed in containing a 0.6-kb deletion. One of the 3.2-kb units contained open reading frames corresponding to trpEG; the remaining units contained trpEG pseudogenes (psi). The nucleotide sequence upstream of trpE contained a region that has characteristics of an origin of replication (ori). Relative to trpB (a chromosomal gene), there were about two copies of the trpEG-containing plasmid. Comparisons of the nucleotide sequences of the 3.2-kb units containing trpEG and psi trpEG indicated that most changes occurred in a 700-nucleotide segment that included the region upstream of trpE and the portion of this gene coding for the N terminus. The consequence of these changes was the silencing of trpEG by inactivation of the putative promoter region and premature termination of the TrpE peptide. In contrast, the nucleotide sequence of the segment corresponding to ori was conserved in the units containing trpEG and psi trpEG. We offer a number of speculations on the evolutionary pressure in this lineage which resulted in the silencing of most of trpEG while still retaining the regions resembling ori.

Animals↗
PubMed1995

Genetics of the tryptophan biosynthetic pathway of the prokaryotic endosymbiont (Buchnera) of the aphid Schlechtendalia chinensis.

Two DNA fragments (3941 and 7152 base pairs) from the procaryotic endosymbiont (Buchnera) of the aphid Schlechtendalia chinensis were cloned and sequenced. The smaller fragment contained trpEG and the larger fragment contained trpDC(F)BA, genes coding for enzymes of the tryptophan biosynthetic pathway which convert chorismate to tryptophan. Both of these gene clusters were present as one copy on the endosymbiont chromosome and probably constitute two transcription units. The deduced amino acid sequences of the proteins was 51-61% identical to the corresponding proteins were previously studied in Buchnera of the aphid Schizaphis graminum. In this endosymbiont, trpEG is amplified and located on a plasmid, whereas, in the endosymbiont of S. chinensis, as in other eubacteria, trpEG occurs as a single copy on the bacterial chromosome. Implications of these findings for the evolution of this mutualistic association are discussed.

Amino Acid Sequence↗
PubMed1995

Genetics, physiology, and evolutionary relationships of the genus Buchnera: intracellular symbionts of aphids.

Evolutionary studies suggest that 200-250 million years ago an aphid ancestor was infected with a free-living eubacterium. The latter became established within aphid cells. Host and endosymbiont (genus Buchnera) became interdependent and unable to survive without each other. The growth of Buchnera became integrated with that of the aphids, which acquired the endosymbionts from their mothers before birth. Speciation of host lineages was paralleled by divergence of associated endosymbiont lineages, resulting in parallel evolution of Buchnera and aphids. Present day Buchnera retains many of the properties of its free-living ancestor, containing genes for proteins involved in DNA replication, transcription, and translation, as well as chaperonins and proteins involved in secretion, energy-yielding metabolism, and amino acid biosynthesis. Some of these processes are also observed in isolated endosymbiont cells. Genetic and physiological studies indicate that Buchnera can synthesize methionine, cysteine, and tryptophan and supply these amino acids to the aphid host. In the case of some fast-growing species of aphids, the overproduction of tryptophan by Buchnera involves plasmid-amplification of the gene coding for anthranilate synthase, the first enzyme of the tryptophan biosynthetic pathway. These recent studies provide a beginning in our understanding of Buchnera and its role in the endosymbiosis with aphids.

Animals↗
PubMed1994

Amplification of trpEG: adaptation of Buchnera aphidicola to an endosymbiotic association with aphids.

Survival of aphids is dependent on an association with a prokaryotic endosymbiont (Buchnera aphidicola) found in specialized cells within the aphid body cavity. Recent nutritional and physiological studies have indicated that one of the functions of the endosymbionts is the synthesis of tryptophan [Douglas, A. E. & Prosser, W. A. (1992) J. Insect Physiol. 38, 565-568]. B. aphidicola resembles in many of its properties free-living prokaryotes. An adaptation to an endosymbiosis involving the overproduction of tryptophan would necessitate alterations that modify the effect of regulatory systems that in free-living organisms function to reduce enzyme activity under conditions of excess tryptophan. We have cloned and sequenced the genes for B. aphidicola trpEG encoding anthranilate synthase, the first enzyme of the tryptophan biosynthetic pathway, which in free-living bacteria is feedback-inhibited by tryptophan. Amino acid sequence comparisons indicate that the B. aphidicola enzyme has all of the key residues involved in allosteric feedback inhibition. Evidence is presented indicating that trpEG is present as four tandem repeats on a circular plasmid. Relative to B. aphidicola trpDC(F)BA (the chromosomal genes coding for the remaining enzymes of the tryptophan biosynthetic pathway) trpEG is amplified 14- to 15-fold. These findings suggest that the effect of inhibition by accumulated tryptophan may be overcome by overproduction of anthranilate synthase. Our results demonstrate the acquisition of a new property (gene amplification) as an adaptation to an endosymbiotic association in which B. aphidicola overproduces tryptophan for the aphid host.

Amino Acid Sequence↗
PubMed1993

Passively transferred antibodies directed against conserved regions of SIV envelope protect macaques from SIV infection.

Inactivated plasma collected from either SIV-infected or peptide-vaccinated macaques was transferred into 17 naive rhesus monkeys. Two additional macaques received normal plasma and served as controls. Following transfer all 19 monkeys were inoculated with SIV. While the controls became infected and were virus-isolation-positive, 3 of 6 recipients of SIV peptide vaccine plasma and 9 of 11 recipients of SIV-infected monkey plasma were protected. None of the 12 protected animals became virus-isolation-positive or seroconverted within 100 days of follow-up. One, however was SIV-PCR-positive. All 12 protected animals were rechallenged 100 days after the initial inoculation; 8 became infected and yielded virus as expected, but 4 remained uninfected. One of the latter was the SIV-PCR-positive monkey mentioned above, suggesting that cryptic SIV infection may be of significance in immunological protection. The results demonstrate that envelope anti-peptide antibodies have similar protective potential in vivo as antibodies directed to the whole virus. In vitro neutralization competition assays performed with sera from vaccinated macaques in the presence of the free peptides suggest that of the four conserved envelope peptides of the vaccine, the two originating from gp41 rather than the two from gp120 are responsible for inducing the neutralizing anti-syncytial activity.

Amino Acid Sequence↗
PubMed1992

Sequence analysis of a DNA fragment from Buchnera aphidicola (an endosymbiont of aphids) containing genes homologous to dnaG, rpoD, cysE, and secB.

The aphid, Schizaphis graminum, contains a prokaryotic, obligately intracellular endosymbiont, Buchnera aphidicola, which is necessary for the survival of the host. A recent study of Bu. aphidicola 16S rRNA has indicated that it is a member of the gamma-3 subdivision of the eubacterial class, Proteobacteria, which includes Escherichia coli. In order to further characterize the endosymbiont and establish its similarity to free-living eubacteria and/or organelles, we have cloned and sequenced a 4534-bp DNA fragment containing dnaG-rpoD-cysE-secB. The deduced amino acid (aa) sequence identity to the homologous E. coli proteins ranged from 47 to 80%. The close proximity of the pair, dnaG-rpoD, to the pair, cysE-secB, on the Bu. aphidicola DNA, differed from E. coli, in which these two pairs of genes are 14 min apart on the bacterial chromosome. The results of past physiological studies of the endosymbiont were consistent with the presence and function of DNA primase (DnaG), sigma factor (RpoD) and components of the secretory system (SecB). Comparison of the deduced aa sequence of Bu. aphidicola CysE (serine acetyltransferase, a key allosterically regulated enzyme in cysteine biosynthesis) with the E. coli wild-type enzyme and a mutant defective in feedback inhibition suggested that the endosymbiont CysE may not be regulated. By analogy with E. coli, the lack of feedback inhibition may lead to overproduction of cysteine by the endosymbiont. The results of this and previous investigations indicate that Bu. aphidicola has many of the properties of free-living bacteria and not of organelles.

Amino Acid Sequence↗
PubMed1992

Inhibitory effect of geniposide on aflatoxin B1-induced DNA repair synthesis in primary cultured rat hepatocytes.

We have previously demonstrated that geniposide (GP) inhibits the aflatoxin B1 (AFB1) induced-hepatotoxicity and hepatic DNA binding in rats. To address the mechanism of action, the effects of GP on AFB1-induced DNA repair synthesis and AFB1 biotransformation in cultured rat hepatocytes were investigated. By evaluation of unscheduled DNA synthesis (UDS), GP reduced AFB1-induced DNA repair synthesis in a dose-dependent manner in hepatocyte cultures. GP elevates the metabolism of AFB1 and decreases the formation of AFM1. The enzyme activities of glutathione S-transferase (GST) and GSH-peroxidase (GSH-Px) in AFB1-treated hepatocyte cultures are enhanced in the presence of GP. GP reduces AFB1-induced DNA repair synthesis through an increased AFB1 detoxication metabolism. It provides one possible mechanism for the chemopreventive activity of GP.

Aflatoxin B1↗