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H T Nguyen

Publications and source records attributed to H T Nguyen.

At least 181 records · Page 10Linked to original sources
PubMed1986

Gene regulation and evolution in the chorion locus of Bombyx mori. Structural and developmental characterization of four eggshell genes and their flanking DNA regions.

We report on the detailed structural and developmental characterization of four chorion genes and a truncated pseudogene located within a 9.5 X 10(3) base chromosomal segment. These genes belong to the A and B multigene families and, like previously characterized moth chorion genes, are arranged in tightly linked pairs, which are divergently transcribed (A/B.L11 and A/B.L12). On the basis of their high degree of sequence divergence, the A genes define two distinct subfamilies, while the more homologous B genes represent different copies of the same gene type. The A.L11 and B.L11 introns are much longer, in each case because of a single inserted DNA segment that is missing from A.L12 or B.L12. The 2.1 X 10(3) base insertion in A.L11 is the first retrovirus-like transposable element characterized in Bombyx mori. The very short 5' flanking sequences of A/B.L11 and A/B.L12 (277 and 276 base-pairs) are distinct as shown by hybridization but both recur in additional chorion gene pairs, forming two respective classes that are expressed during distinctly different developmental periods. The divergently transcribed genes of each pair, which border the same 5' flanking sequence, are expressed co-ordinately, during the same developmental period. Detailed comparisons of the 5' flanking regions, and of the corresponding region of the Drosophila s15-1 chorion gene, revealed numerous, very short sequence elements that are shared. One such element, T-C-A-C-G-T, is also associated with all five sequenced Drosophila chorion genes. Some elements are repeated in a dyad symmetrical pattern, i.e. are associated with each of the two genes in a pair, while others, including T-C-A-C-G-T, occur only once per 5' flanking region, and, if functionally important, would presumably act bi-directionally on both genes of the pair.

Animals↗
PubMed1986

Remote-site stimulation of influenza antibodies in monkeys following intestinal stimulation.

Antibodies in nasal secretions and saliva were stimulated in 10 monkeys (Macacus rhesus) which had been immunized orally with a killed influenza vaccine. Prior to immunization, monkeys had no detectable antibody to influenza virus hemagglutinin or neuraminidase in sera or secretions. Oral immunization (6 times within 12 days, total of 0.6 mg hemagglutinin (HA) and 240 neuraminidase units) using intraesophageal intubation induced secretory antibodies to both antigens, but no serum antibody. Six and 8 monkeys reacted with HA-antibodies in nasal secretions and saliva, respectively, whereas neuraminidase antibodies occurred in nasal secretions of all 10 and in the saliva of 9 animals. The results support the concept of a common mucosal immune system in monkeys.

Administration, Oral↗
PubMed1985

A xanthomatous lesion resembling balloon cell melanoma of the iris and ciliary body of a dog.

A slow-growing xanthomatous tumour which diffusely infiltrated the iris and ciliary body of a dog was composed of large, pale, vacuolated cells which contained scattered fine pigment granules. Electron microscopy revealed coalescing vacuoles, lamellar membranous structures, and small groups of melanosomes in the cytoplasm, suggesting melanocytic origin. The lesion resembled balloon cell melanoma of the ciliary body of man. The behaviour of the tumour was benign. This is a clinical and pathological entity which has not been reported previously in the dog.

Animals↗
PubMed1985

Intricate combinatorial patterns of exon splicing generate multiple regulated troponin T isoforms from a single gene.

Mechanisms of alternative RNA splicing, important in the generation of protein diversity, are common but incompletely understood. Among the contractile proteins, troponin T exists in several isoforms, shown to be derived in part from a novel pattern of differential RNA splicing in the 3' region of the rat skeletal fast troponin T gene. In fact, this gene has a previously unsuspected capacity to encode multiple isoforms. The isolation of four distinct but related cDNAs from this gene, which share discontinuous subsegments of sequence identity in their 5' regions, and the determination of the genomic sequence, demonstrate that small exons with characteristic split codon structure are differentially spliced in intricate combinatorial patterns to generate a minimum of 10, and potentially 64, distinct troponin T mRNAs, encoding different isoforms, in a developmentally regulated and tissue-specific manner. At least two of these mRNAs are spliced from structurally identical primary transcripts, necessitating control by trans-acting factors.

Amino Acid Sequence↗
PubMed1985

Treatment of experimental lens capsular tears with intense focused ultrasound.

High-intensity focused ultrasound was employed to seal lens capsular tears in a rabbit model. Ultrasound therapy was applied either contiguously, thereby completely covering the tear, or in a discrete exposure pattern around the tear. Both methods prevented the formation of a generalised cataract. This was in contrast to results observed in a group of control (untreated) animals which all developed generalised lens opacities. Each control animal also developed a local lens opacity at the site of the capsular tear, as did half the animals treated with the discrete pattern. No animal treated with contiguous exposures developed any local or generalised traumatic-type cataract other than the small lens opacity immediately produced by the treatment. These treatment cataracts would not constitute a significant impediment to vision so long as they did not fall on the visual axis.

Animals↗
PubMed1985

Animal studies of toxic shock syndrome.

Toxic shock syndrome (TSS) was first described in 1978 and since that year over 2990 cases have been reported to the Communicable Disease Center. The estimated case-fatality rate is 5.6%. The disease is characterized by fever, hypotension, rash, desquamation, and involvement of at least three other organ systems. Approximately 85% of the cases are menstrually related and tampon use has been identified as a risk factor. The remaining 15% of the cases occur in both sexes and are not specifically related to age or geographic location. In all cases where sought there is evidence for infection by Staphylococcus aureus. Nearly all S. aureus isolates are phage type 52/29 and elaborate a unique exotoxin (toxic shock toxin). This review explores both the successful and unsuccessful attempts to induce toxic shock or a TSS-like syndrome in animals other than man. The review identifies the baboon as an animal model of TSS and discusses the clinical and pathologic sequellae, in this species, after exposure to purified toxic shock toxin.

Animals↗
PubMed1984

A novel mechanism of alternative RNA splicing for the developmentally regulated generation of troponin T isoforms from a single gene.

Troponin T (TnT) is a major regulatory protein of the striated muscle that exhibits developmental and tissue-specific structural heterogeneity. The molecular basis for this heterogeneity was studied at the level of TnT structural gene organization and RNA expression. Two tissue-specific and developmentally regulated TnT mRNAs, alpha and beta, are derived from a single fast skeletal muscle TnT gene. Although otherwise structurally identical from amino acid 70 to the end of the 3' untranslated region, the alpha and beta TnT mRNAs differ by a small internal oligonucleotide coding for amino acids 229 to 242. These isoform-specific oligopeptides, both spanning the same internal portion of the TnT protein, are encoded by two distinct and adjacent miniexons in the TnT gene. Alternative and mutually exclusive splicing of these two miniexons results in the incorporation of either exon into the mature TnT mRNA and argues persuasively against a processive scanning model of RNA splice site selection.

Animals↗
PubMed1983

Transcriptional and cell cycle-mediated regulation of myosin heavy chain gene expression during muscle cell differentiation.

The molecular mechanisms regulating the induction of myosin heavy chain (MHC) gene expression during muscle cell differentiation were studied using a MHC cDNA recombinant plasmid. During in vitro L6E9 cell myogenesis, cytoplasmic MHC mRNA content/cell nucleus increases a minimum of 500-fold during the first 6 days of differentiation. Two independent parameters regulating MHC mRNA accumulation were directly measured. (i) Intrinsic (chemical) MHC mRNA stability (t1/2 = 55-60 h) is the same in both myotubes and when first detected in myoblasts. This suggests that the intrinsic stability of the MHC mRNA molecule does not change during myogenesis. (ii) The rate of MHC gene transcription and MHC mRNA synthesis increases approximately 100-fold during myogenesis but is insufficient to account for the entire MHC mRNA accumulation. An additional independent parameter was found to profoundly affect MHC mRNA accumulation. Withdrawal from the cell cycle, as occurs during terminal myogenic differentiation, increases the final accumulation of stable mRNAs, such as MHC, by increasing mRNA effective stability. During L6E9 myogenesis, the transition from mitotically active myoblasts (doubling time = 16 h) to postmitotic myotubes results in a 4-5-fold increase in the effective stability of cytoplasmic MHC mRNA. This cell cycle-mediated effect, combined with the induction of MHC mRNA synthesis, completely accounts for MHC mRNA accumulation. A parallel effect occurs in the total cytoplasmic poly(A)+ mRNA population. The rates of synthesis of each of the two major stability components (t1/2 = 5 and 50 h, respectively) are equally increased 2-3-fold during myogenesis. However, the composition of the cytoplasmic mRNA population changes due to the preferential accumulation of stable mRNAs. We conclude that both transcriptional and cell cycle-mediated regulation of MHC gene expression is necessary, but either alone is not sufficient to produce the differentiated muscle cell phenotype.

Animals↗
PubMed1983

Characterization of sarcomeric myosin heavy chain genes.

Myosin heavy chain is encoded by a large multigene family. Using pMHC-25, a recombinant cDNA clone isolated from the rat myogenic cell line L6E9, four members of this family in the rat have been isolated and shown to be tissue-specific and developmentally regulated. The coding regions of these genes share regions of homology interspaced with regions of non-homology. Detailed analysis of one embryonic and one adult myosin heavy chain gene shows that the coding sequences are interrupted by numerous intervening sequences whose number, size, and distribution do not appear to be conserved in the same organism or between species.

Animals↗
PubMed1983

Reversibility of muscle differentiation in the absence of commitment: analysis of a myogenic cell line temperature-sensitive for commitment.

The interrelationship between commitment (irreversible withdrawal from the cell cycle) and muscle-specific gene expression was analyzed with the myogenic cell line ts 3b-2, which is temperature sensitive for commitment and cell fusion. The rates of synthesis and levels of accumulation of muscle-specific mRNAs and proteins in the ts 3b-2 cells at permissive and nonpermissive temperatures are comparable, indicating that neither commitment nor cell fusion is required for induction of muscle-specific gene expression. In the absence of commitment, the cells are reversibly withdrawn from the cell cycle during gene induction, and expression of the muscle-specific genes is deinduced upon the switch to growth-stimulating conditions. The deinduction reflects coordinate and preferential cessation of muscle-specific mRNA synthesis, coupled with destabilization of the muscle-specific mRNAs in the cytoplasm, without effect on constitutively expressed housekeeping protein genes. The phenotype of the ts 3b-2 cells demonstrates that commitment and muscle-specific gene expression are both required, but alone are insufficient, to produce the terminally differentiated muscle phenotype.

Actins↗
PubMed1983

Inhibition of muscle differentiation by trypanosoma cruzi.

L6E9 rat myoblasts were infected in tissue culture with the myotropic Brazil strain of Trypanosoma cruzi. The effect of parasite infection on the ability of myoblasts to differentiate into myotubes was studied. Both morphological and biochemical differentiation were found to be profoundly affected by parasitic infection in a dose-related fashion. Evidence is presented to suggest that infected myoblasts can no longer differentiate. Differentiation, once underway, seemed unaffected by the parasitic infection; biochemical markers of differentiation remained intact.

Actins↗
PubMed1983

Indirect immunoperoxidase test for the diagnosis of paratuberculosis.

An indirect immunoperoxidase procedure for the diagnosis of paratuberculosis was described. Formalin-fixed ileocecal tissue containing large numbers of Mycobacterium paratuberculosis organisms was used as the source of antigen. Goat anti-bovine immunoglobulin G labeled with peroxidase was used as the conjugate in the test system. The method is relatively simple to do and may prove to be valuable as a routine screening test.

Animals↗
PubMed1983

Effects of large doses of phenylbutazone administration to horses.

The effects of large doses of phenylbutazone were evaluated in clinically normal horses. The drug was given to 4 groups of 2 horses each at the rate of 30 mg/kg of body weight, orally, or 30, 15, or 8 mg/kg IV daily for up to 2 weeks. All horses became anorectic and depressed after 2 to 4 phenylbutazone treatments, and the horses given 15 or 30 mg/kg died on or between days 4 and 7 of treatment. A decrease in total blood neutrophil count occurred in all horses, and was associated with toxic left shift in horses given the 2 larger dosage schedules. The horses also had progressive increases in serum urea nitrogen, creatinine, and phosphorus concentrations, accompanied by decreasing serum calcium concentrations. There was a progressive decrease in total serum protein in all 8 horses. Gastrointestinal ulcerations, renal papillary necrosis, and vascular thromboses were the predominant postmortem findings.

Animals↗
PubMed1982

Sarcomeric myosin heavy chain is coded by a highly conserved multigene family.

pMHC25, a recombinant plasmid containing myosin heavy chain (MHC) cDNA sequences from differentiated myotubes of the L6E9 rat cell line, has been shown to hybridize to all sarcomeric MHC mRNAs so far tested but not to nonsarcomeric MHC mRNAs. In addition, pMHC25 hybridizes to multiple restriction endonuclease-digested fragments of rat genomic DNA corresponding to different MHC genomic sequences. Thus, the MHC gene represented by pMHC25 is a member of a sarcomeric MHC multigene family that has regions of sequence homology shared among its members. This sarcomeric MHC multigene family has been estimated to be composed of a minimum of seven genes, some of which are polymorphic in the rat. We have also determined that pMHC25 hybridizes to MHC gene sequences in genomic DNA of all species that have striated muscle, ranging from nematodes to man. Sarcomeric MHC genes, therefore, have been horizontally and vertically conserved in evolution. Additionally, we have used the pMHC25 plasmid to demonstrate that MHC genes do not undergo rearrangement or amplification during muscle cell differentiation.

Animals↗
PubMed1982

Scanning electron microscopic study of lead effects on cerebral astrocytes in primary culture.

The effects of lead acetate on the cell surface of primary cultured astrocytes from dissociated neonatal rat cerebrums were studied using scanning electron microscopy. Astrocytes, grown for two weeks in a modified Eagle's minimal essential medium containing 20% calf serum, were exposed to lead (1, 10, 30, 50, or 100 micrograms Pb/ml) for four days. Astrocytes grown in lead-free medium showed membrane folds (ruffles) and microvilli on the surfaces of perikarya. Vesicular structures or blebs (gliosomes) were scattered on the surfaces of perikarya and branched cell processes. Cultures exposed to 1 microgram Pb/ml were indistinguishable from controls. After exposure to 10 and 30 micrograms Pb/ml, microvilli disappeared, membrane folds were less extensive, and the number of surface blebs increased. Astrocytes exposed to 50 micrograms Pb/ml showed no surface membrane folds or microvilli while the blebs increased sufficiently to cover the surface of the perikarya. Cells treated with the highest lead concentration (100 micrograms/ml) were shrunken and perikarya again were covered with blebs. Transmission electron microscopy of the cells exposed to 10-100 micrograms Pb/ml showed membrane bound vacuoles and areas of cytoplasmic clearing, some of which may correspond to the surface blebs seen by SEM. These studies suggest that the changes in the cell surface resulting from lead exposure represent a toxic effect of lead on primary cultured astrocytes.

Animals↗
PubMed1981

Circular dichroism and magnetic circular dichroism of reduced molybdenum-iron protein of Azotobacter vinelandii nitrogenase.

Studies of the circular dichroism (CD) and magnetic circular dichroism (MCD) of the dithionite-reduced molybdenum-iron protein of Azotobacter vinelandii nitrogenase (Av1) are reported. CD and MCD are measurable at room temperature across a wide spectral range, from the near-UV to the near-IR. The visible-near-UV CD is insignificantly affected by moderate variations in pH, temperature, ionic strength, and buffer, providing evidence against conformational change in the range studied. Mg2+ and ATP also cause no observable change in the visible-near-UV CD. Both CD and MCD in the visible-near-UV are unaffected by 30% inactivation by O2. However, the CD and MCD spectra of uncrystallized Av1 differ very significantly from those of crystallized Av1; in particular, the MCD spectrum is very sensitive to the presence of heme impurities. The identicality in both CD and MCD spectra of the reduced molybdenum-iron proteins from Azotobacter vinelandii and Klebsiella pneumoniae shows that these proteins contain metal clusters, identical in number, structure, and protein environment. While the absorption, CD, and MCD spectra of reduced Av1 are typical in many respects of simpler iron-sulfur proteins and are most similar to the [Fe4S4(SR)4]3- clusters found in reduced bacterial ferredoxins, significant differences exist. It is concluded, therefore, that the clusters present are not identical with those previously characterized, a conclusion earlier arrived at from electron paramagnetic resonance, Mössbauer, and EXAFS spectroscopies.

Azotobacter↗