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T Xu

Publications and source records attributed to T Xu.

At least 145 records · Page 8Linked to original sources
PubMed1992

Cholesterol pools in rat adrenal mitochondria: use of cholesterol oxidase to infer a complex pool structure.

ACTH stimulates the side-chain cleavage of cholesterol in the adrenal cortex in a cycloheximide-inhibitable manner. Its mechanism involves mobilizing cholesterol to a "steroidogenic pool" where the sterol can be metabolized to pregnenolone. This pool has been proposed to be in the inner mitochondrial membrane where cytochrome P-450scc resides, and regulation may involve transport of cholesterol from the outer to the inner membrane. To investigate the structure of the mitochondrial cholesterol pools, cholesterol oxidase has been used as a membrane-impermeant probe which should have selective access to outer membrane cholesterol. At 37 C, almost all the cholesterol in mitochondria from ether-stressed rats was metabolized by cholesterol oxidase. Depletion of an intermembrane space but not a matrix marker enzyme indicated partial disruption of the outer membrane. However, at 16 C, mitochondria remained largely intact, and cholesterol oxidase identified a unique pool of cholesterol, which was about two-thirds of the total. In experiments using mitochondria from ether-stressed rats, the size of the 16 C cholesterol oxidase accessible and inaccessible pools was compared with that of the steroidogenic pool. The steroidogenic pool was enhanced by pretreatment of some animals with aminoglutethimide (a P-450scc inhibitor) or eliminated with cycloheximide, both of which increased the total mitochondrial cholesterol. This approach reveals that the steroidogenic pool is not equivalent to the cholesterol oxidase-inaccessible pool. Rather, it overlaps both the cholesterol oxidase accessible and inaccessible pools. These results are not consistent with a simple two pool model, but can be explained by assuming a minimum of three cholesterol pools.

Adrenal Cortex↗
PubMed1992

The involvement of the Notch locus in Drosophila oogenesis.

The Notch gene in Drosophila encodes a transmembrane protein with homology to EGF that, in a variety of tissues, appears to mediate cell interactions necessary for cell fate choices. Here we demonstrate that oogenesis and spermatogenesis depend on Notch. We examine the phenotypes of the temperature-sensitive Notch allele, Nts1, and, using a monoclonal antibody, determine the cellular and subcellular distribution of Notch protein during oogenesis. We show that Nts1 is associated with a missense mutation in the extracellular, EGF homologous region of Notch and that at non-permissive temperatures oogenesis is blocked and the subcellular distribution of the protein is altered. In wild-type ovaries, Notch protein is found on the apical surface of somatically derived follicle cells, while in the germline-derived cells the protein is not polarized. These findings are discussed in view of the hypothesis that Notch acts as a multifunctional receptor to mediate developmentally important cell interactions.

Animals↗
PubMed1992

[Ultrastructural examination and stereological study of bone marrow megakaryocytes in children with idiopathic thrombocytopenic purpura].

The ultrastructure and surface architecture of megakaryocytes (MK) were examined in 19 children with idiopathic thrombocytopenic purpura (ITP), the stereological parameters of alpha granules were computed. Transmission electron microscopy revealed vacuolization of cytoplasma of MKs, decrease in the number of alpha granules and degeneration of mitochondria. The granular MKs of chronic ITP appeared to be focal distribution of demarcation membrane system (DMS) in two cases with formation of large membrane complex. Staining with tannic acid indicated vesicular, tubular and cisternal dilation of DMA. Rough endoplasmic reticulum and Golgi complex were much more abundant than in normal MKs. In 5 cases of ITP, we found emperipolesis of hematopoietic cells within MKs. Under scanning electron microscopy many MKs showed complex surface processes including crowded blebs, villi and giant irregular projections. Occasionally perforations on the surface membrane could be seen. Stereological analysis showed that the Nv, Vv, and Sv of alpha granules of both acute and chronic ITP were markedly decreased as compared with normal control (P < 0.001), and the Nv of acute ITP was notably less than that of chronic ITP (P < 0.05). However the S/V, M.DIAM. and M. VOL. were no significant difference among normal control, acute and chronic ITP (P > 0.05).

Bone Marrow↗
PubMed1991

Anticandidal activity of major human salivary histatins.

We have previously shown that histatins 1, 3, and 5 are homologous, histidine-rich proteins present in human parotid and submandibular secretions which contain 38, 32, and 24 amino acids, respectively. Interest in these proteins stems from the fact that histatins exhibit candidacidal and candidastatic activities. The goal of the present investigation was a detailed functional characterization of these anticandidal activities of histatins at the levels of killing of blastoconidia, killing of germinated cells, and inhibition of germination by using three bioassays. Candidacidal activities were evaluated at several ionic strengths, in the presence of different mono- and divalent ions, and at multiple pH values. In addition, the susceptibility of Candida albicans in different growth phases to histatins was investigated. While all three major human histatins demonstrated candidacidal activities, they differed in their abilities to kill blastoconidia and germinated cells, with histatin 5 being the most active, histatin 3 showing moderate activity, and histatin 1 exhibiting the lowest level of activity. For the inhibition of germination, however, histatin 3 exhibited more activity than either histatin 1 or histatin 5. The candidacidal activity of histatins was inversely proportional to both the ionic strength and the divalent cation concentration in the medium. Stepwise reduction of the pH of the assay medium enhanced the candidacidal activities of histatins 1 and 3, while the activity of histatin 5 was pH independent over the range of pHs 4 to 8. C. albicans in log-phase growth was more susceptible to histatins 1 and 3 than cells in stationary phase. Cells in either growth phase were still more vulnerable to histatin 5 than to histatins 1 and 3. The results obtained establish the functional relationship of the major histatins with respect to both their fungicidal and fungistatic activities and provide insights into their activities under ionic and pH conditions likely to be encountered in vivo in the oral cavity. Moreover, the data point towards possible mechanisms responsible for the anticandidal activities of histatins.

Amino Acid Sequence↗
PubMed1991

[Relationship between central beta-endorphins and serotonin systems in mechanism of hypoxic ventilatory regulation].

Experiments were performed on anesthetized bilaterally chemodenervated rabbits. After giving hypoxic gas mixture (10% O2 in N2) to animals to cause ventilatory inhibition, lateral ventricle applications of beta-endorphins (beta-EP) antagonist naloxone (Nlx) and agonist ohmefentanyl (OMF) respectively reduced and enhanced hypoxia-induced ventilatory inhibition. Meanwhile the level of central serotonin (5-HT) was obviously increased more than that before the drug administration. Injection of exogenous 5-HT into rabbit lateral ventricle induced central beta-EP content to decrease markedly while minute ventilation (VE) was returned to control at the same time. The results suggest that beta-EP system in CNS is the basic and direct element in the regulatory mechanism of hypoxic ventilatory inhibition, and central 5-HT system only acts as a neuromodulator in modulating the activity of beta-EP system to indirectly affect ventilatory response to hypoxia.

Animals↗
PubMed1991

[The study on calcium ion concentration specificity in meridian and acupoint in rabbit].

Ion selected "Acupuncture electrode" was introduced for detection of calcium ion concentration in meridians and acupoints in rabbit. It was demonstrated that the calcium ion concentration was significant higher than that in the location of non-meridian and non-acupoint. This is the first and important finding of physicochemical characteristics of meridians.

Acupuncture Points↗
PubMed1990

Molecular interactions between the protein products of the neurogenic loci Notch and Delta, two EGF-homologous genes in Drosophila.

Genetic analyses have raised the possibility of interactions between the gene products of the neurogenic loci Notch and Delta, each of which encodes a transmembrane protein with EGF homology. To examine the possibility of intermolecular association between the products of these two genes, we studied the effects of their expression on aggregation in Drosophila S2 cells. We find that Notch-expressing cells form mixed aggregates specifically with cells that express Delta and that this process is calcium dependent. In addition, we show that Notch and Delta can associate within the membrane of a single cell, and further, that they form detergent-soluble intermolecular complexes. Our analyses suggest that Notch and Delta proteins interact at the cell surface via their extracellular domains.

Animals↗
PubMed1990

deltex, a locus interacting with the neurogenic genes, Notch, Delta and mastermind in Drosophila melanogaster.

The Notch locus of Drosophila melanogaster, which codes for a transmembrane protein sharing homology with the mammalian epidermal growth factor, is one of a small number of zygotically acting genes, the so called neurogenic loci, which are necessary for the correct segregation of neural from epidermal lineages during embryogenesis. In an attempt to identify genes whose products may interact with that of Notch, we designed a genetic screen aimed at identifying suppressors of certain Notch mutations which are known to affect the extracellular epidermal growth factor homologous domain of Notch. Mutations in two neurogenic loci were identified as suppressors: Delta, whose product was recently shown to interact with Notch and mastermind. In addition, a third, X-linked gene was shown capable of acting as a suppressor. We show that this gene is the deltex locus, characterize the phenotype of deltex mutations, and demonstrate both a maternal and zygotic action of the locus. All deltex alleles behave as recessive viables affecting wing, ocellar and eye morphology. There are allele specific interactions between deltex and various Notch alleles; for example, deltex mutants with a reduced dosage of wild-type Notch die as pupae. deltex also interacts with Delta and mastermind in a fashion that is formally analogous to its interaction with Notch. These results emphasize the special relationship between Notch, Delta and mastermind suggested by previous work and indicate that deltex is likely to play an important role in the same genetic circuitry within which these three neurogenic loci operate.

Alleles↗
PubMed1990

The Notch locus and the genetic circuitry involved in early Drosophila neurogenesis.

The genetic and molecular analysis of the Notch locus, which codes for a transmembrane protein sharing homology with the mammalian epidermal growth factor, suggests that the Notch protein is involved in a cell interaction mechanism essential for the differentiation of the embryonic nervous system of Drosophila. Taking advantage of the negative complementation between two Notch mutations that affect the extracellular domain of the protein, we have tried to dissect the genetic circuitry in which Notch is integrated by searching for genes whose products may interact with the Notch protein. This genetic screen has led to the identification of a surprisingly restricted set of interacting loci, including Delta and mastermind. Like Notch, both of these genes belong to a group of loci, the neurogenic loci, which have been previously identified by virtue of their similar mutant phenotype affecting early neurogenesis. We extend these studies by systematically exploring interactions between specific mutations in the Notch molecule and the other neurogenic genes. Furthermore, we show that the molecular lesions of two Notch alleles (nd and nd2), which interact dramatically with mastermind mutations, as well as with a mutation affecting the transducin homologous product of the neurogenic locus Enhancer of split, involve changes in the intracellular domain of the protein.

Alleles↗
PubMed1990

Structural relationship between human salivary histatins.

Histatins are a group of electrophoretically distinct histidine-rich polypeptides with microbicidal activity found in human parotid and submandibular gland secretions. Recently, we have shown that histatins 1, 3, and 5 are homologous proteins that consist of 38, 32, and 24 amino acid residues, respectively, and that these polypeptides kill the pathogenic yeast, Candida albicans. We now describe the isolation and structural characterization of histatins 2, 4, 6, and 7-12, the remaining members of this group of polypeptides. Histatin 2 was found to be identical to the carboxyl terminal 26 residues of histatin 1; histatin 4 was found to be identical to the carboxyl terminal 20 residues of histatin 3; and histatin 6 was found to be identical to histatin 5, but contained an additional carboxyl terminal arginine residue. The amino acid sequences of histatins 7-12 formally correspond to residues 12-24, 13-24, 12-25, 13-25, 5-11, and 5-12, respectively, of histatin 3, but could also arise proteolytically from histatin 5 or 6. These results establish, for the first time, the complete structural relationships between all members of this group of microbicidal proteins in human parotid saliva. The relationship of histatins to one another is discussed in the context of their genetic origin, biosynthesis and secretion into the oral cavity, and potential as reagents in anti-candidal studies.

Amino Acid Sequence↗
PubMed1990

Primary structure and anticandidal activity of the major histatin from parotid secretion of the subhuman primate, Macaca fascicularis.

A major macaque histatin (M-histatin 1) from the parotid secretion of the subhuman primate, Macaca fascicularis, was isolated by gel filtration on Bio-Gel P-2 and purified to homogeneity by reversed-phase high-performance liquid chromatography on a TSK-ODS C18 column. The complete amino acid sequence of M-histatin 1, determined by automated Edman degradation, is: (formula; see text) M-histatin 1 contains 38 amino acid residues, a phosphoserine at residue 2, has a molecular weight of 4881.8, a calculated pI of 8.5, and histidine forms 26.3% of the mass. The hydropathicity plot of M-histatin 1 predicts that the molecule is entirely hydrophilic, and Chou-Fasman secondary prediction indicates that the polypeptide is devoid of alpha-helix and beta-sheet conformation in aqueous solutions but contains a series of beta turns. M-histatin 1 includes a six-amino-acid insert (residue 10-15) not present in human histatins and, with the introduction of gaps to maximize homology, it displays 89% and 91% sequence similarity with human histatins 1 and 3, respectively. M-histatin 1 exhibited fungicidal and fungistatic effects against the dimorphic pathogen, Candida albicans, in three separate bioassays. Its anticandidal effects were comparable with or greater than those of human histatins 1, 3, and 5. M-histatins 2, 3, and 4 were not sequenced directly because insufficient materials were available, but the amino acid composition of M-histatin 3 was nearly identical to that of the N-terminal 20 amino acid residues of M-histatin 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1990

Perforating branches of the basilar bifurcation.

The perforating branches of the upper basilar artery and of the first (P1) segment of the posterior cerebral artery were studied in 50 fixed brains obtained from human cadavers. No vertical branches arose from the basilar bifurcation. The upper basilar artery gave rise to horizontal branches, which were studied with reference to their angle of origin. Perforating arteries arising from P1 segments were found in all specimens. Rare branches were found to come from the inferior and anterior surfaces of P1 segments. The anatomical patterns of these branches are discussed in the light of previous reports. Preoperative knowledge of some anatomical aspects (the position of the basilar apex, the angle between the right P1 and left P1 segments, and relationships to the dorsum sellae and the mammillary bodies) can help in the selection of a neurosurgical approach and may improve the operative results in the surgical treatment of basilar apex aneurysms.

Basilar Artery↗
PubMed1990

Influence of morphine microinjected into head of caudate nucleus on electric activities of nociceptive neurons in parafascicular nucleus of rat thalamus.

Morphine (8 micrograms/microliter) was injected into the head of the caudate nucleus (CN). The pain-discharges of the pain-excitation neurons (PEN) in the parafascicular nucleus (Pf) were inhibited, ie, decreasing in frequency of pain-discharges and lengthening in latent period of pain-discharges. The inhibitory effect of the pain-inhibition neurons (PIN) in the Pf induced by noxious peripheral stimulation were relieved, ie, increasing the firing rate and shortening the inhibitory duration. The opiate receptor antagonist naloxone (0.75 mg/kg, ip) blocked the above effects of morphine. These results suggest that the intracaudate opioid peptide system play an important role in the modulation of pain information in the Pf of thalamus.

Animals↗
PubMed1990

[The influences of morphine microinjected into preoptic area on electric activities of pain response neurons in parafascicular nucleus of thalamus in rat].

We have observed the influences of opioid-like substances in preoptic area (POA) on the electric activities of pain response neurons in parafascicular nucleus of thalamus (Pf). The results were as follows: 1. Morphine 10 micrograms/microliters or 1 micrograms/microliters microinjected into POA could remarkably inhibit the pain discharges of most (20/26, 19/23 respectively) pain excitatory neurons (PEN) in Pf. The frequency of evoked discharges was decreased nd the duration was shortened. After injecting 10 micrograms/microliters morphine, three neurons showed inhibitory responses to noxious stimuli. 2. Morphine of the two doses could shorten the complete inhibitory period of pain inhibitory neurons (PIN, 23/33). These results suggest that the opioid-like substances in POA might have an inhibitory effects on pain response neurons in Pf.

Animals↗
PubMed1989

[Midline peripheral T-cell lymphoma--an immunohistochemical and electron microscopy study].

Twenty-six cases of nasal/nasopharyngeal midline peripheral T-cell lymphomas were studied clinically and pathologically with immunohistochemical markers and electronmicroscopy. A clearer understanding of the nature of midline malignant reticulosis has obtained. Immunohistochemical markers confirmed that except 5 small specimens which failed to show the monoclonal growth, 18 cases had peripheral T-cell lymphomas, 15 had TH, 3 Ts and 2 B-Cell lambda light chain and 1 HC. Morphological observations showed that 24 cases out of 26 exhibited middle and small polymorphic T-cells. This tumor had distinctive clinical features and was characterized by midfacial progressive necrosis, slow growth, local invasion and rarely metastasis, often with prominent granulomatous and vascular proliferation. Therefore, a discrimination of this disease from midline malignant reticulosis and midfacial destructive lesions is absolutely necessary.

Adult↗
PubMed1988

Histatins, a novel family of histidine-rich proteins in human parotid secretion. Isolation, characterization, primary structure, and fungistatic effects on Candida albicans.

Histatins 1, 3, and 5 from human parotid secretion were isolated by gel filtration on Bio-Gel P-2 and reverse phase high performance liquid chromatography. The complete amino acid sequences of histatins determined by automated Edman degradation of the proteins, Staphylococcus aureus V8 protease, and tryptic peptides, are as follows: (Sequence: see text). Histatins 1, 3, and 5 contain 38, 32, and 24 amino acid residues, have molecular weights of 4929, 4063, and 3037, respectively, and contain 7 residues of histidine. Histatin 1 contains 1 mol of phosphate/mol of protein; histatins 3 and 5 lack phosphate. With the exception of Glu (residue 4) and Arg (residue 11) in histatin 1, the first 22 amino acid residues of all three histatins are identical, and the carboxyl-terminal 7 residues of histatins 1 and 3 are also identical. The sequence, -Glu-Phe-Pro-Phe-Tyr-Gly-Asp-Tyr-Gly- (residues 23-29), in histatin 1 is absent in histatin 3; and the sequence, -Gly-Tyr-Arg- (residues 23-25), in histatin 3 is absent in histatin 1. The complete sequence of histatin 5 is contained within the amino terminal 24 residues of histatin 3. The structural data suggest that histatins 1 and 3 are derived from different structural genes, whereas histatin 5 is a proteolytic product of histatin 3. All three histatins exhibit the ability to kill the pathogenic yeast, Candida albicans.

Amino Acid Sequence↗