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Biomedical subjects

X Yu

Publications and source records attributed to X Yu.

At least 55 records · Page 3Linked to original sources
PubMed2001

Domain structure and dynamics in the helical filaments formed by RecA and Rad51 on DNA.

Both the bacterial RecA protein and the eukaryotic Rad51 protein form helical nucleoprotein filaments on DNA that catalyze strand transfer between two homologous DNA molecules. However, only the ATP-binding cores of these proteins have been conserved, and this same core is also found within helicases and the F1-ATPase. The C-terminal domain of the RecA protein forms lobes within the helical RecA filament. However, the Rad51 proteins do not have the C-terminal domain found in RecA, but have an N-terminal extension that is absent in the RecA protein. Both the RecA C-terminal domain and the Rad51 N-terminal domain bind DNA. We have used electron microscopy to show that the lobes of the yeast and human Rad51 filaments appear to be formed by N-terminal domains. These lobes are conformationally flexible in both RecA and Rad51. Within RecA filaments, the change between the "active" and "inactive" states appears to mainly involve a large movement of the C-terminal lobe. The N-terminal domain of Rad51 and the C-terminal domain of RecA may have arisen from convergent evolution to play similar roles in the filaments.

DNA↗
PubMed2001

The human erythropoietin receptor gene rescues erythropoiesis and developmental defects in the erythropoietin receptor null mouse.

Erythropoietin and its receptor are required for definitive erythropoiesis and maturation of erythroid progenitor cells. Mice lacking the erythropoietin receptor exhibit severe anemia and die at about embryonic day 13.5. This phenotype can be rescued by the human erythropoietin receptor transgene. Animals expressing only the human erythropoietin receptor survived through adulthood with normal hematologic parameters and appeared to respond appropriately to induced anemic stress. In addition to restoration of erythropoiesis during development, the cardiac defect associated with embryos lacking the erythropoietin receptor was corrected and the increased apoptosis in fetal liver, heart, and brain in the erythropoietin receptor null phenotype was markedly reduced. These studies indicate that no species barrier exists between mouse and human erythropoietin receptor and that the human erythropoietin receptor transgene is able to provide specific expression in hematopoietic and other selected tissues to rescue erythropoiesis and other organ defects observed in the erythropoietin receptor null mouse.

Anemia↗
PubMed2001

Expression of a micro-protein.

The smallest known open reading frame encodes the ribosomal protein L41, which in yeast is composed of only 24 amino acids, 17 of which are arginine or lysine. Because of the unique problems that might attend the translation of such a short open reading frame, we have investigated the properties and the translation of the mRNAs encoding L41. In Saccharomyces cerevisiae L41 is encoded by two linked genes, RPL41A and RPL41B. These genes give rise to mRNAs that have short 5' leaders of 18 and 22 nucleotides and rather long 3' leaders of 203 and 210 nucleotides not including their poly(A) tails. The mRNAs are translated exclusively on monosomes, suggesting that ribosomes do not remain attached to the mRNA after termination of translation. Calculations based on the abundance of ribosomes and of L41 mRNA indicate that the entire translation event, from initiation through termination, must occur in approximately 2 s. Termination of translation after only 25 codons does not subject the mRNAs encoding L41 to nonsense-mediated decay. Surprisingly, despite the L41 ribosomal protein being conserved from the archaea through the mammalia, S. cerevisiae can grow relatively normally after deletion of both RPL41A and RPL41B.

3' Untranslated Regions↗
PubMed2001

Involvement of Bcl-2 family genes and Fas signaling system in primary and secondary male germ cell apoptosis induced by 2-bromopropane in rat.

Epidemiological surveys and animal experimental studies suggest that exposure to 2-bromopropane (2-BP) could result in reproductive and hematopoietic disorders. The objectives of this study were to investigate the role of apoptosis in 2-BP-induced testicular toxicity and whether this process involves Bcl-2 family genes and the Fas signaling system. Rats were injected percutaneously with 1350 mg/kg 2-BP for 1 to 5 days and then were euthanized at 6 or 12 h after one dose, 6 h after two, three, or five doses, and 2 or 9 days after the final treatment. Light and electron microscopic analyses, TUNEL staining of DNA fragments, agarose gel electrophoresis of low-molecular-weight DNA, and Western blotting analysis of Bcl-2 family proteins and Fas receptor and ligand were conducted. Two-day treatment resulted in selective degeneration of spermatogonia with marked nuclear chromatin condensation. DNA ladder formation on the agarose gel further validated the findings of TUNEL-stained apoptotic cells. The percentage of apoptotic-positive tubules and apoptotic cell index increased time dependently. 2-BP treatment resulted in two distinct morphological changes: an immediate effect on spermatogonia and secondary apoptosis of spermatocytes 9 days after treatment. Downregulation of Bcl-2 after the first or second injection of 2-BP and upregulation of Bax after the first treatment contributed to the initiation of primary apoptosis of spermatogonia. Expression of FasL was inhibited while expression of Fas increased after the 2-BP treatment and remained at levels about two times of the control. However, it increased about sixfold of the control by day 9 after final injection, which contributed to the induction of secondary apoptosis of spermatocytes. Our results indicate that 2-BP resulted in apoptotic death of testicular germ cells and that this process involves the Bcl-2 family genes and the Fas signaling system.

Animals↗
PubMed2001

Advances in transplantation tolerance.

Immunosuppressive drugs developed in the past two decades have improved the short-term survival of organ allografts, but tolerance has not been achieved and almost all transplant recipients continue to require drugs throughout life. Graft rejection arises from the cognate interaction of T cells with antigen-presenting cells, the recognition of alloantigen through the T-cell receptor, and the delivery of accessory stimulation signals. Once activated by the specific antigen, replicating T cells die if they are re-exposed to the same antigen. Since depletion of antigen-activated T cells is one critical mechanism of transplantation tolerance, drugs such as ciclosporin that interfere with activation-induced T-cell death could inhibit tolerance, whereas drugs such as mycophenolate mofetil, that induce the death of activated T cells, could facilitate tolerance. Other tolerance mechanisms depend on inactivation rather than elimination of allograft reactive T cells. When antigen recognition occurs without costimulation through the CD28 and CD154 accessory receptors, or in absence of cell division, T cells become unresponsive. Thus, inhibitors of CD28 and CD154, and inhibition of T-cell division by rapamycin promotes transplantation tolerance.

CD28 Antigens↗
PubMed2001

Crystallization and preliminary X-ray crystallographic studies of wild-type human ornithine transcarbamylase and two naturally occurring mutants at position 277.

Wild-type human ornithine transcarbamylase (OTCase) and two mutants (R277Q and R277W) that cause 'late-onset' hyperammonemia were crystallized and a preliminary structure determination was carried out. The unliganded wild-type enzyme crystallizes in the cubic space group I23, with unit-cell parameters a = b = c = 203.4 A. R277Q crystallizes in two crystal forms under the same crystallization conditions. One crystal form is isomorphous to that of unliganded wild-type crystals, with unit-cell parameters a = b = c = 202.2 A. The second form also belongs to a cubic space group, P4(3)32, but has unit-cell parameters a = b = c = 139.8 A. R277W crystals are isomorphous to the second crystal form of R277Q, with unit-cell parameters a = b = c = 138.7 A. None of these crystal forms is isomorphous to other crystal forms of OTCase that have been studied. The structures in both crystal forms have been solved using molecular replacement. In the first crystal form there are two monomers in the asymmetric unit, corresponding to a solvent content of 75%. Because of its high molecular and crystal symmetry and the presence of non-crystallographic symmetry, this structure could not be solved with AMoRe or X-PLOR, but was solved successfully with COMO. There is only one monomer in the asymmetric unit in the second crystal form, corresponding to a solvent content of 62%. This structure was successfully solved with AMoRe.

Crystallization↗
PubMed2001

Study on the degeneracy of antisense peptides using affinity chromatography.

The degeneracy of antisense peptides was studied by high-performance affinity chromatography. A model sense peptide (AAAA) and its antisense peptides (CGGG, GGGG, RGGG, SGGG) were designed and synthesized according to the degeneracy of genetic codes. An affinity column with AAAA as the ligand was prepared. The affinity chromatographic behaviors of antisense peptides on the column were evaluated. The results indicated that model antisense peptides have clear retention on the immobilized AAAA affinity column. RGGG showed the strongest affinity interaction. Similar result was obtained from another experiment that Arg-substituted antisense peptide of fusion peptide (1-11) of influenza virus A was also shown the highest affinity binding to immobilized fusion peptide.

Amino Acid Sequence↗
PubMed2001

Human ornithine transcarbamylase: crystallographic insights into substrate recognition and conformational changes.

Two crystal structures of human ornithine transcarbamylase (OTCase) complexed with the substrate carbamoyl phosphate (CP) have been solved. One structure, whose crystals were prepared by substituting N-phosphonacetyl-L-ornithine (PALO) liganded crystals with CP, has been refined at 2.4 A (1 A=0.1 nm) resolution to a crystallographic R factor of 18.4%. The second structure, whose crystals were prepared by co-crystallization with CP, has been refined at 2.6 A resolution to a crystallographic R factor of 20.2%. These structures provide important new insights into substrate recognition and ligand-induced conformational changes. Comparison of these structures with the structures of OTCase complexed with the bisubstrate analogue PALO or CP and L-norvaline reveals that binding of the first substrate, CP, induces a global conformational change involving relative domain movement, whereas the binding of the second substrate brings the flexible SMG loop, which is equivalent to the 240s loop in aspartate transcarbamylase, into the active site. The model reveals structural features that define the substrate specificity of the enzyme and that regulate the order of binding and release of products.

Amino Acid Sequence↗
PubMed2001

Lipid-based microtubular drug delivery vehicles.

Lipid microtubules that self-assemble from a diacetylenic lipid are suitable structures for the sustained release of bioactive agents. Microtubules were loaded with agents under aqueous conditions and embedded in an agarose hydrogel for localization at areas of interest. Protein release from our microtubule-hydrogel delivery system was characterized in vitro, and in vivo biocompatibility was examined. The influences of protein molecular weight and initial loading concentration on release profile were evaluated by releasing test proteins myoglobin, albumin, and thyroglobulin. Protein molecular weight inversely affected the release rate, and loading with a higher protein concentration increased the mass but not the percent of initially loaded protein released daily. Preservation of protein activity was demonstrated by the ability of a neurotrophic factor released from the delivery system to induce neurite extension in PC12 cells. Bovine aortic smooth muscle cells co-cultured with the microtubule-hydrogel system showed no evidence of cytotoxicity and proliferated in the presence of the microtubules. Subcutaneous implantation of microtubules in rodents revealed no significant inflammatory response after 10 days. Our microtubule-hydrogel system is useful for applications where sustained release without contact between agent and organic solvents is desired.

Animals↗
PubMed2001

A primitive sarcopterygian fish with an eyestalk.

The discovery of two Early Devonian osteichthyan (bony fish) fossils has challenged established ideas about the origin of osteichthyans and their divergence into actinopterygians (teleosts and their relatives) and sarcopterygians (tetrapods, coelacanths, lungfishes and related groups). Psarolepis from China and an unnamed braincase from Australia combine derived sarcopterygian and actinopterygian characters with primitive features previously restricted to non-osteichthyans, suggesting that early osteichthyan evolution may have involved substantial parallellism between sarcopterygians and actinopterygians. But interpretation of these fossils has been hampered by poor phylogenetic resolution. Here we describe a basal sarcopterygian fish, Achoania gen, et sp. nov., that fills the morphological gap between Psarolepis and higher sarcoptergyians. We also report the presence of eyestalk attachments in both Achoania and Psarolepis, showing that this supposedly non-osteichthyan feature occurs in basal sarcopterygians as well as the actinoptergyian-like Australian braincase.

Animals↗
PubMed2001

[Urodynamic characteristics of patients with tethered cord syndrome and its clinical significance].

OBJECTIVE: To evaluate the urodynamic characteristics of children with tethered cord syndrome (TCS) and its clinical significance. METHODS: We conducted urodynamic studies in 94 cases of TCS who underwent microsurgical release within one week preoperatively and 3 to 6 months postoperatively. RESULTS: 80 out of 94 (85.1%) children with TCS presented with lower urinary tract symptoms. Neuropathic injuries were found both in patients in group A (with lower urinary tract symptoms) and in 11 out of 14 patient in group B (without lower urinary tract symptoms). The maximum urethral closing pressure (MUCP) and maximum detrusor pressure (MDP) were significantly lower in group alpha (without upper urinary tract injury), which were 45 cm H(2)O +/- 18 cm H(2)O and 27 cm H(2)O +/- 15 cm H(2)O respectively, than in group beta (with upper urinary tract injury), which were 69 cm H(2)O +/- 24 cm H(2)O and 44 cm H(2)O +/- 17 cm H(2)O respectively, while bladder compliance (BC) in group alpha (5.6 cm H(2)O +/- 0.9 ml/cm H(2)O) was significantly higher than in group beta (2.5 ml/cm H(2)O +/- 1.2 ml/cm H(2)O). MUCP, MDP and BC were improved in group I (primary TCS) after cord untethering, 32 cm H(2)O +/- 14 cm H(2)O, 21 cm H(2)O +/- 12 cm H(2)O, 9.5 ml/cm H(2)O +/- 1.3 ml/cm H(2)O postoperatively and 63 cm H(2)O +/- 245 cm H(2)O, 37 cm H(2)O +/- 156 cm H(2)O, 5.1 ml/cm H(2)O +/- 0.8 ml/cm H(2)O preoperatively respectively, while in group II remained unchangeable. CONCLUSION: Urodynamic studies are effective methods to identify neuropathic characteristics of lower urinary tract symptom in children with TCS and to find neuropathic injury during subclinical period. According to urodynamic studies, increase of MUCP and DP and decrease of BC are high risk factors of vesicoureteral reflux and upper urinary tract injury. Microsurgical release can improve bladder function in primary TCS, while do no good to bladder function in secondary TCS.

Adolescent↗
PubMed2001

p53-dependent radiation-induced crypt intestinal epithelial cells apoptosis is mediated in part through TNF-TNFR1 system.

Radiation induces apoptosis of crypt intestinal epithelial cells (IEC) through a pathway that is largely dependent on p53. However, exactly how p53 mediates IEC apoptosis is unclear. Studies in vitro suggest that one mechanism by which p53 mediates apoptosis is through its ability to transactivate members of the TNF receptor family of 'Death Receptors'. Here, we examined the role of one of its member, TNF receptor type 1 (TNFR1), in an in vivo model of p53-dependent radiation-induced IEC apoptosis. We demonstrate that mice genetically engineered to be deficient in TNF receptor type 1 (TNFR1(-/-)) and mice injected with TNFR1-fusion chimeric protein (TNFR1-Fc; a competitive inhibitor of TNFR1) were partially protected (30-40%) from p53-dependent radiation-induced IEC apoptosis. However, we found no evidence to support the possibility p53 transcriptionally regulates the expression of TNFR1 nor increases the susceptibility of IEC to TNF-mediated apoptosis. Interestingly, we found that injection of TNF readily induced IEC apoptosis and that radiation induced a p53-dependent increase in the intestinal level of TNF. Furthermore, injection of a neutralizing anti-TNF mAb reduced p53-dependent radiation-induced IEC apoptosis by approximately 60%. Overall, these results suggest that p53-dependent radiation-induced IEC apoptosis is mediated in part through ability of p53 to regulate TNF, which subsequently induces IEC apoptosis through TNFR1.

Animals↗
PubMed2001

[Combination treatment for craniopharyngiomas with stereotactic intracavitary irradiation and gamma knife surgery].

OBJECTIVE: To evaluate the effectiveness of the combination treatment for craniopharygiomas with stereotactic intracavitary irradiation and gamma knife surgery. METHODS: Combination treatment of stereotactic instillation of radioisotopes and gamma knife surgery was performed in 46 patients with craniopharyngioma between October 1996 and June 1999. There were 24 men and 22 women, with age ranging from 3 to 60 years (average 38.6 years). There were 13 solid tumors and 33 mixed solid and cystic tumors. Twenty-eight patients had undergone prior caraniotomies with total or partial resection of tumors, with or without followed external beam radiation therapy. Gamma knife surgery was done in solid tumors and the combination treatment was done in mixed tumors: the cyst being treated with stereotactic intracavitary radiation and the solid part with Gamma knife. RESULTS: Thirty-eight patients (10 solid and 28 mixed) were followed up from 6 months to two years (averaged 16 months). The tumor control rate (disappeared, decreased and unchanged) was 90% in solid tumor, 85.7% in mixed tumors, and 92.1% in solid segment and the total control rate was 89.5%. CONCLUSION: The combination treatment is a simple, safe and effective method for craniopharyngiomas, especially for the recurrent mixed solid and cystic tumors. Gamma knife surgery plays an important role in the treatment of solid component of the craniopharyngiomas.

Adolescent↗
PubMed2001

Anti-CD69 autoantibodies cross-react with low density lipoprotein receptor-related protein 2 in systemic autoimmune diseases.

We investigated whether autoantibodies to CD69, one of the earliest markers of lymphocyte activation, exist in the sera of patients with systemic autoimmune disease. Serum samples were obtained from patients with rheumatoid arthritis (RA), systemic lupus erythematosus, and Behcet's disease, and were tested for the presence of anti-CD69 autoantibodies by ELISA and Western blotting using rCD69 fusion proteins. IgG-type autoantibodies to CD69 were detected in the sera of 38.3% of the RA patients, 14.5% of the systemic lupus erythematosus patients, and 4.0% of the patients with Behcet's disease. Among those with RA, the anti-CD69 autoantibody-positive patients had a higher serum level of rheumatoid factors and a more accelerated erythrocyte sedimentation rate than the anti-CD69 autoantibody-negative patients. Further, the predominant epitope on the CD69 molecule to which most of the anti-CD69 autoantibody-positive serum samples exclusively reacted, was mapped at the C terminus of CD69. Of interest, this epitope is homologous to a stretch of amino acids in the protein sequence of low-density lipoprotein receptor-related protein 2 (LRP2), which is a receptor for multiple ligands including beta-very low density lipoprotein and is also an autoantigen responsible for Heymann nephritis in rats. The anti-CD69 autoantibody cross-reacted to LRP2 through the homologous amino acid sequence. To our knowledge, this is the first evidence of the existence of anti-CD69 autoantibodies. This autoantibody may modulate the function of CD69- and LRP2-expressing cells.

Adult↗
PubMed2001

DNA-mediated protection against classical swine fever virus.

Four eukaryotic expression plasmids containing the entire E2 gene sequence of classical swine fever virus (CSFV) were constructed: (a) pcDST, with 5' signal and 3' transmembrane sequences; (b) pcDSW, with 5' signal sequence only; (c) pcDWT, with transmembrane sequences only; and (d) pcDWW, containing the E2 gene alone. All four plasmids were readily transfected into BHK-21 cells, with pcDST and pcDSW resulting in secretion of E2 antigen. The latter two plasmids were also shown to induce a humoral immune response against CSFV in mice when administered intramuscularly, but no immune responses were detected with either pcDWT or pcDWW. The antibody level elicited by pcDSW was higher than that induced by pcDST. When pcDSW was used to immunize rabbits and pigs, both species were shown to be protected from challenge with virulent CSFV (hog cholera lapinized virus for rabbits and Shimen strain for pigs).

Animals↗
PubMed2001

Neurotoxicity of 2-bromopropane and 1-bromopropane, alternative solvents for chlorofluorocarbons.

To clarify the neurotoxicity of 2-bromopropane (2-BP) in comparison with 1-bromopropane (1-BP), 36 Wistar strain male rats were divided into 4 groups of 9 and exposed daily to 100-ppm 2-BP, 1000-ppm 2-BP, 1000-ppm 1-BP, or fresh air for 8 h a day. Exposure to 1000 ppm of 1-BP was discontinued after 5 or 7 weeks' exposure because of the unexpected appearance of incomplete hindlimb paralysis followed by serious emaciation. The other groups were sacrificed at the end of 12 weeks' exposure. Exposure to 1000 ppm of 2-BP resulted in significant decreases in body weight and motor nerve conduction velocity (MCV) and elongation in distal latency (DL). A ball-like enlargement of myelin sheaths was observed. Significant reductions in the number of erythrocytes, platelets, and leukocytes, testicular germ cell loss, and seminiferous atrophy were also observed in this group, but not in 100-ppm 2-BP group. Exposure to 1000 ppm of 1-BP for 5 or 7 weeks caused a significant decrease in body weight and MCV and elongation in DL. Linearly arranged ovoid- or bubble-like debris of the axons and myelin sheaths in the teased tibial nerves and axonal swelling in gracilis nucleus were found in this group. No significant changes in hematological indices or histopathological findings of the testis were found in this group. In conclusion, 2-BP is neurotoxic to the peripheral nerves in addition to its toxic effects on the reproductive and hematopoietic systems at 1000 ppm. No noticeable changes were found in the rats exposed to 100 ppm of 2-BP. 1-BP is a potent neurotoxicant at 1000 ppm for 5 or 7 weeks, while testicular and hematopoietic toxicity was not found.

Animals↗
PubMed2001

Electron microscopic studies of the translin octameric ring.

Translin is thought to participate in a variety of cellular activities including chromosomal translocations, translational regulation of mRNA expression, and mRNA transport. It forms an octameric ring structure capable of sequence-specific binding of both DNA and RNA substrates. We have used electron microscopy and single-particle image analysis to generate a three-dimensional reconstruction of the Translin ring. The subunits appear to have two distinct domains that assemble to form an open channel with diameter of approximately 30 A at one end and approximately 50 A at the opposite end. In the presence of either DNA or RNA containing consensus binding sequences, the largest opening into the central cavity is filled with density. Strikingly, although Translin shows significant sequence homology to only one other protein, Translin-associated factor X, the quaternary organization and the dimerization of subunits in the ring are very similar to those observed for hexameric ring helicases. This suggests that many of the structures in DNA and RNA metabolism may have similar quaternary organization.

Algorithms↗