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Biomedical subjects

L Bi

Publications and source records attributed to L Bi.

15 recordsLinked to original sources
PubMed2000

Nucleotide excision repair/TFIIH helicases RAD3 and SSL2 inhibit short-sequence recombination and Ty1 retrotransposition by similar mechanisms.

Eukaryotic genomes contain potentially unstable sequences whose rearrangement threatens genome structure and function. Here we show that certain mutant alleles of the nucleotide excision repair (NER)/TFIIH helicase genes RAD3 and SSL2 (RAD25) confer synthetic lethality and destabilize the Saccharomyces cerevisiae genome by increasing both short-sequence recombination and Ty1 retrotransposition. The rad3-G595R and ssl2-rtt mutations do not markedly alter Ty1 RNA or protein levels or target site specificity. However, these mutations cause an increase in the physical stability of broken DNA molecules and unincorporated Ty1 cDNA, which leads to higher levels of short-sequence recombination and Ty1 retrotransposition. Our results link components of the core NER/TFIIH complex with genome stability, homologous recombination, and host defense against Ty1 retrotransposition via a mechanism that involves DNA degradation.

Adenosine Triphosphatases↗
PubMed1999

Proliferative defect and embryonic lethality in mice homozygous for a deletion in the p110alpha subunit of phosphoinositide 3-kinase.

Phosphatidylinositol 3,4,5-trisphosphate is a phospholipid signaling molecule involved in many cellular functions including growth factor receptor signaling, cytoskeletal organization, chemotaxis, apoptosis, and protein trafficking. Phosphorylation at the 3 position of the inositol ring is catalyzed by many different 3-kinases (classified as types IA, IB, II, and III), but the physiological roles played by each of the different 3-kinase isozymes during embryonic development and in homeostasis in animals is incompletely understood. Mammalian type IA kinase isozymes are heterodimers that are active at 37 degrees C when the catalytic 110-kDa subunit interacts through an amino-terminal binding domain with a regulatory 85- or 55-kDa subunit. Using gene targeting in embryonic stem cells, we deleted this binding domain in the gene encoding the alpha isoform of the 110-kDa catalytic subunit (Pik3ca) of the alpha isozyme of the type IA kinases, leading to loss of expression of the p110 catalytic subunit. We show that Pik3cadel/del embryos are developmentally delayed at embryonic day (E) 9.5 and die between E9.5 and E10.5. E9. 5 Pik3cadel/del embryos have a profound proliferative defect but no increase in apoptosis. A proliferative defect is supported by the observation that fibroblasts from Pik3cadel/del embryos fail to replicate in Dulbecco's modified Eagle's medium and fetal calf serum, even with supplemental growth factors.

Animals↗
PubMed1999

Inhibitor antibody development and T cell response to human factor VIII in murine hemophilia A.

In order to understand better the mechanism of inhibitor formation in hemophilia A patients, we have characterized the immune response to human factor VIII in a murine model of hemophilia A. Mice with severe factor VIII deficiency caused by targeted gene disruptions in exons 16 and 17 were injected intravenously with human factor VIII. Anti-factor VIII was absent or was detected at only very low levels in hemophilic mice of both strains after a single injection of 0.2 microg factor VIII, but it was present in most mice after a second exposure. Subsequent exposures led to high titer anti-factor VIII antibodies in both ELISA and inhibitor assays. A human factor VIII-specific T cell proliferative response was detected with spleen cells obtained three days after a single injection with human factor VIII, before mice had detectable anti-factor VIII antibodies. Subsequent exposures to factor VIII were followed by an increased T cell proliferative response. These studies indicate that murine hemophilia A is a good model for the study of the immune response to human factor VIII, especially the role of the T cell in the early steps in inhibitor antibody formation.

Animals↗
PubMed1998

[The clinical study on labor pain relief using two kinds of segmental block anesthesia].

OBJECTIVE: To study the pain relief effectiveness of combined subarachnoid peridural segmental block and simple peridural anesthesia, and their influences on the mothers and the infants. METHODS: 100 pregnants women were administered combined subarachnoid and peridural segmental block during labor and delivery (study group). 40 pregnant women received simple peridural anesthesia (control group). The degree of labour pain, side effects, labor course, the mode of delivery and the incidences of postpartum hemorrhage, fetal distress and neonatal asphyxia were observed in two groups respectively. RESULTS: The pain relief effect in the study group was much better than that of the control group (P < 0.01). There were no significant differences of the mean time of labor course and the mode of delivery between the two groups (P > 0.05). The incidences of postpartum hemorrhage, fetal distress and neonatal asphyxia were similar (P > 0.05). CONCLUSION: The analgesic delivery of combined subarachnoid and peridural segmental block is safe and effective, which has no influences on the labour course and the mothers and infants. Its pain relief effectiveness is more positive and satisfactory than that of simple peridural anesthesia. We suggest that it should be performed in the medical units under optimal conditions.

Adjuvants, Anesthesia↗
PubMed1998

[Effect of trichosanthin of cell cycle and apoptosis of murine melanoma cells].

OBJECTIVE: To study the inhibitory effect of purified trichosanthin component on the proliferation of malignant melanoma. METHODS: The effect of purified trichosanthin component on the DNA synthesis, cell cycle and cell apoptosis of murine melanoma cells were detected by flowcytometry when cultured in vitro. RESULTS: The significant G0/G1 phase arrest was revealed by the increase of cells in G0/G1 phase and decrease of cells in S phase. The obvious apoptosis of melanoma cells was induced by purified trichosanthin component. G0/G1 phase arrest was highly correlated with apoptosis (r = 0.8705). CONCLUSIONS: The purified trichosanthin component can markedly inhibit melanoma cells by the suppression of DNA synthesis in S phase and cell mitosis as well as induction of cell apoptosis.

Animals↗
PubMed1998

[High-level expression of human immunodeficiency virus type 1 gp120 protein in E. coli].

In order to improve protein expression and to produce good and cheap diagnostic antigen, the gene fragment (560bp) in N-terminal of gp120 of HIV-1 LAV strain was amplified by PCR. After digested by EcoR I and Sal I, the fragment was cloned into a high-level expression vector pET28a. The recombinant plasmid pET/120 transfecting BL21 (DE3) produced the protein with high-level expression in the host cell BL21(DE3), which was further proved having good antigenicity and high specificity by indirect ELISA and Western-blot assay. The protein expressed was about 50% of the total bacterial protein by SDS-PAGE electrophoresis test. It was highly expressed in the prokaryotic expression system.

Cloning, Molecular↗
PubMed1996

Further characterization of factor VIII-deficient mice created by gene targeting: RNA and protein studies.

Previously we created two strains of factor VIII-deficient mice by insertion of a neo gene into (1) the 3' end of exon 16 and (2) exon 17 of the factor VIII gene. Affected mice of both strains have no plasma factor VIII activity, yet are healthy with no spontaneous bleeding. Factor VIII-deficient females bred with affected males survive pregnancy and delivery. We used reverse transcriptase-polymerase chain reaction of liver RNA to characterize factor VIII mRNA processing. Factor VIII mRNA of the exon 16 knockout strain contains neo sequences plus 17 bp of intron 16 due to use of a cryptic donor site in intron 16. All factor VIII mRNA of the exon 17 knockout strain lacks exon 17 and neo sequences. In skipping exon 17, the intron 16 donor site or a cryptic donor site 46 bp 3' to the intron 16 donor site are used. Thus, factor VIII deficiency in exon 16 knockout mice is due to truncated protein, while in exon 17 knockout mice it is due to either truncated or partially deleted protein. After immunizing exon 16 knockout mice with human recombinant factor VIII, two monoclonal antibodies were obtained that recognize < 100 pg of mouse factor VIII light chain. Assay of cryoprecipitate from the plasma of affected mice failed to show factor VIII light chain.

Animals↗
PubMed1995

Targeted disruption of the mouse factor VIII gene produces a model of haemophilia A.

Haemophilia A is a classic X-linked disease which affects 1 in 5-10,000 males in all populations and is caused by defects in coagulation factor VIII. Roughly 60% of patients have severe disease with factor VIII activity < 1% of normal; they have frequent spontaneous bleeding into joints, soft tissues, muscles and internal organs. These patients usually require regular injections of plasma-derived or recombinant human factor VIII. Because this is expensive and can potentially lead to life-threatening complications, other forms of therapy, including gene therapy, have been proposed. Natural canine models of factor VIII and factor IX deficiency have been available for many years, and gene therapy attempts on these dogs have met with partial success. However, a small animal model of the disease is desirable for studies of factor VIII function and gene therapy. Using gene targeting, we have made a mouse with severe factor VIII deficiency.

Animals↗
PubMed1993

Spectrum of mutations in CRM-positive and CRM-reduced hemophilia A.

Hemophilia A is due to the functional deficiency of factor VII (FVIII, gene locus F8C). Although half the patients have no detectable FVIII protein in their plasma, the more rare patients (approximately 5%) have normal levels of a dysfunctional FVIII and are termed cross-reacting material (CRM)-positive. More commonly (approximately 45%), patients have plasma FVIII protein reduced to an extent roughly comparable to the level of FVIII activity and are designated CRM-reduced. We used denaturing gradient gel electrophoresis to screen for mutations within the F8C gene of 11 patients (6 CRM-positive, 5 CRM-reduced) and identified 9 different mutations in 9 patients after analyses of all 26 exons, the promoter region, and the polyadenylation site. Six mutations have not been described previously. Five were missense (Ser289Leu, Ser558Phe, Val634Ala, Val634-Met, Asn1441Lys), and the sixth was a 3-bp deletion (delta Phe652). A review of the literature and the assay of FVIII antigen in 5 hemophilia A patients with previously identified missense mutations from this laboratory yielded a total of 20 other unique CRM-reduced and CRM-positive mutations. Almost all CRM-positive/reduced mutations (24/26) were missense, and many (12/26) occurred at CpG dinucleotides. We examined 19 missense mutations for evolutionary conservation using the portions of the porcine and murine F8C sequences that are known, and 18/19 amino acid residues altered by mutation in these patients were conserved. Almost 50% of mutations (11/26) clustered in the A2 domain, suggesting that this region is critical for the function of FVIII.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗