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Biomedical subjects

C Li

Publications and source records attributed to C Li.

At least 19 recordsLinked to original sources
PubMed2006

The wheat and barley vernalization gene VRN3 is an orthologue of FT.

Winter wheat and barley varieties require an extended exposure to low temperatures to accelerate flowering (vernalization), whereas spring varieties do not have this requirement. In this study, we show that in these species, the vernalization gene VRN3 is linked completely to a gene similar to Arabidopsis FLOWERING LOCUS T (FT). FT induction in the leaves results in a transmissible signal that promotes flowering. Transcript levels of the barley and wheat orthologues, designated as HvFT and TaFT, respectively, are significantly higher in plants homozygous for the dominant Vrn3 alleles (early flowering) than in plants homozygous for the recessive vrn3 alleles (late flowering). In wheat, the dominant Vrn3 allele is associated with the insertion of a retroelement in the TaFT promoter, whereas in barley, mutations in the HvFT first intron differentiate plants with dominant and recessive VRN3 alleles. Winter wheat plants transformed with the TaFT allele carrying the promoter retroelement insertion flowered significantly earlier than nontransgenic plants, supporting the identity between TaFT and VRN-B3. Statistical analyses of flowering times confirmed the presence of significant interactions between vernalization and FT allelic classes in both wheat and barley (P < 0.0001). These interactions were supported further by the observed up-regulation of HvFT transcript levels by vernalization in barley winter plants (P = 0.002). These results confirmed that the wheat and barley FT genes are responsible for natural allelic variation in vernalization requirement, providing additional sources of adaptive diversity to these economically important crops.

Adaptation, Physiological↗
PubMed2006

Torsion of the central pair microtubules in eukaryotic flagella due to bending-driven lateral buckling.

Inspired by recent interest in torsion of the central pair microtubules in eukaryotic flagella, a novel thin-walled elastic beam model is suggested to study critical condition under which uniform bending of a flagellum will cause lateral/torsional buckling of the central pair. The model is directed to the central pair itself and the role of all surrounding cross-linkings inside the flagellum is modeled as an equivalent surrounding elastic medium. The model predicts that bending-driven torsion of the central pair does occur when the radius of curvature of the bent flagellum reduces to a moderate critical value typically of tens of microns. In particular, this critical value is almost independent of the flagellum length, and more sensitive to the parameters defining the surrounding elastic medium than the shear modulus of microtubules. The predicted wavelengths of the torsional buckling mode are insensitive to the flagellum length and comparable to some known related experimental data. These results indicate that torsion of the central pair microtubules in flagella is inevitable as a result of bending-driven lateral buckling. This offers an entirely new insight into the ongoing research on the mechanism of the central pair torsion.

Animals↗
PubMed2006

Identification of molecular markers and signaling pathway in endometrial cancer in Hong Kong Chinese women by genome-wide gene expression profiling.

Endometrial cancer is the third most common gynecologic malignancy and the ninth most common malignancy for females overall in Hong Kong. Approximately 80% or more of these cancers are endometrioid endometrial adenocarcinomas. The aim of this study was to reveal genes contributing to the development of endometrioid endometrial cancer, which may impact diagnosis, prognosis and treatment of the disease. Whole-genome gene expression analysis was completed for a set of 55 microdissected sporadic endometrioid endometrial adenocarcinomas and 29 microdissected normal endometrium specimens using the Affymetrix Human U133 Plus 2.0 oligonucleotide microarray. Selected genes of interest were validated by quantitative real-time-polymerase chain reaction (qRT-PCR). Pathway analysis was performed to reveal gene interactions involved in endometrial tumorigenesis. Unsupervised hierarchical clustering displayed a distinct separation between the endometrioid adenocarcinomas and normal endometrium samples. Supervised analysis identified 117 highly differentially regulated genes (>or=4.0-fold change), which distinguished the endometrial cancer specimens from normal endometrium. Twelve novel genes including DKK4, ZIC1, KIF1A, SAA2, LOC16378, ALPP2, CCL20, CXCL5, BST2, OLFM1, KLRC1 and MBC45780 were deregulated in the endometrial cancer, and further validated in an independent set of 56 cancer and 29 normal samples using qRT-PCR. In addition, 10 genes were differentially regulated in late-stage cancer, as compared to early-stage disease, and may be involved in tumor progression. Pathway analysis of the expression data from this tumor revealed an interconnected network consisting of 21 aberrantly regulated genes involved in angiogenesis, cell proliferation and chromosomal instability. The results of this study highlight the molecular features of endometrioid endometrial cancer and provide insight into the events underlying the development and progression of endometrioid endometrial cancer.

Endometrial Neoplasms↗
PubMed2006

Genetic diversity of Picea asperata populations based on RAPDs.

The genetic diversity of ten natural populations of Picea asperata Mast. were studied using RAPD markers. A total of 160 reproducible fragments were produced from the ten primers used. The mean number of fragments detected per individual was 114.7. Altogether 120 fragments were polymorphic among the ten populations, none of them were found to be population-specific. Nei's expected heterozygosity (H (e)) ranged from 0.233 to 0.269, and the average was 0.247. The analysis of molecular variance revealed that the coefficient of gene differentiation among populations, based on F (ST) and the unbiased estimate PhiST, equaled 0.224 and 0.290, respectively. Such high values indicate that there is significant differentiation among populations, which could result from several factors, including restricted gene flow between populations (Nm = 0.866). Founder events may be another factor attributing to the high level of genetic differentiation. In addition, it was discovered that the geographic distribution is not correlated with the genetic distances among the populations of P. asperata.

Genetic Markers↗
PubMed2006

Modeling growth factor activity during proinflammatory stress: methodological considerations in assessing cytokine modulation of IGF binding proteins released by cultured bovine kidney epithelial cells.

The present research was conducted to model potential mechanisms through which IGFBPs might be affected by a key proinflammatory response initiating cytokine tumor necrosis factor (TNF-)-alpha. Madin-Darby bovine kidney epithelial (MDBK) cells, known to release IGFBPs in response to several stimuli, were grown under several conditions and challenged with forskolin (F) or recombinant TNF-alpha for 24h. Forskolin increased IGFBP-3 gene expression and media content of BP-3 protein. TNF-alpha increased basal and augmented F-mediated IGFBP-3 gene expression. However, TNF-alpha effects on the measurable media content of IGFBPs were influenced by culture conditions; in the absence of added protease inhibitors (PIs) or sufficient media albumin concentration (high BSA, 1mg/ml), the effect of TNF-alpha was to decrease (P<0.02) measurable IGFBPs. In the presence of PI and high BSA, media IGFBP-3 levels were shown to be increased by TNF-alpha consistent with the gene expression data. Changes in media IGFBP-3 protease activity were examined further to explain the observed effects of TNF-alpha on production and destruction of IGFBPs in media. When recombinant human IGFBP-3 (500 ng/ml) was added to PI-free, low BSA 100 microg/ml) media from TNF-treated MDBK cells, less than 10% of the BP-3 was recognizable by Western blot in 30 min; conversely, inclusion of High BSA and PI in media resulted in attenuation of the protease effect on the IGFBPs. The data suggest that the MDBK model of cellular response to proinflammatory stimulus is affected by culture conditions and that TNF-alpha affects media content of IGFBPs through effects on IGFBP gene expression coupled with degradation of IGFBPs via enhanced proteolytic enzyme release.

Animals↗
PubMed2006

Mutation analysis of the FRAS1 gene demonstrates new mutations in a propositus with Fraser syndrome.

Fraser syndrome (OMIM 219000) is a rare, autosomal recessive condition with classical features of cryptophthalmos, syndactyly, ambiguous genitalia, laryngeal, and genitourinary malformations, oral clefting and mental retardation. Mutations causing loss of function of the FRAS1 gene have been demonstrated in five patients with Fraser syndrome. However, no phenotype-genotype correlation was established and there was evidence for genetic heterogeneity. Fraser syndrome is rare and the FRAS1 gene has 75 exons, complicating mutation screening in affected patients. We have screened two patients who fulfilled the diagnostic criteria for Fraser syndrome and three patients with related phenotypes (two patients with Manitoba oculotrichoanal syndrome and one patient with unilateral cryptophthalmos and labial fusion) for mutations in FRAS1 to increase the molecular genetic data in patients with Fraser syndrome and related conditions. We report two new mutations in a patient with Fraser syndrome, a frameshift mutation and a deletion of two amino acids that we consider pathogenic as both alter the NG2-like domain of the protein. Although we are still unable to clarify a phenotype-genotype relationship in Fraser syndrome, our data add to the list of mutations associated with this syndrome.

Adolescent↗
PubMed2006

Length-dependence of flexural rigidity as a result of anisotropic elastic properties of microtubules.

Unexplained length-dependence of flexural rigidity and Young's modulus of microtubules is studied using an orthotropic elastic shell model. It is showed that vibration frequencies and buckling load predicted by the accurate orthotropic shell model are much lower than that given by the approximate isotropic beam model for shorter microtubules, although the two models give almost identical results for sufficiently long microtubules. It is this inaccuracy of the isotropic beam model used by all previous researchers that leads to reported lower flexural rigidity and Young's modulus for shorter microtubules. In particular, much lower shear modulus and circumferential Young's modulus, which only weaken flexural rigidity of shorter microtubules, are responsible for the observed length-dependence of the flexural rigidity. These results confirm that longitudinal Young's modulus of microtubules is length-independent, and the observed length-dependence of the flexural rigidity and Young's modulus is a result of strongly anisotropic elastic properties of microtubules which have a length-dependent weakening effect on flexural rigidity of shorter microtubules.

Anisotropy↗
PubMed2006

Enhanced stress tolerance in transgenic pine expressing the pepper CaPF1 gene is associated with the polyamine biosynthesis.

ERF/AP2 transcription factors play an important role in plant stress tolerance. However, little is known about the functional significance of ERF/AP2 genes in pine, compared to the model plant species Arabidopsis. Capsicum annuum pathogen and freezing tolerance-related protein 1 (CaPF1) is an ERF/AP2 transcription factor. We show here that overexpression of CaPF1 resulted in a dramatic increase in tolerance to drought, freezing, and salt stress in a gymnosperm species, eastern white pine (Pinus strobus L.). Measurement of polyamines demonstrated that the levels of putrescine (Put), spermidine (Spd), and spermine (Spm) did not increase but remain constant in CaPF1-overexpressed eastern white pine, whereas the levels decreased in the controls, probably increasing the ability of transgenic callus cultures and plants to stress tolerance. These results demonstrated that enhanced stress tolerance in transgenic pine expressing the pepper CaPF1 gene is associated with the polyamine biosynthesis and this pepper transcription factor may be used to engineer pine species for multiple stress tolerance.

Adaptation, Physiological↗
PubMed2006

Structure of magainin and alamethicin in model membranes studied by x-ray reflectivity.

We have investigated the structure of lipid bilayers containing varied molar ratios of different lipids and the antimicrobial peptides magainin and alamethicin. For this structural study, we have used x-ray reflectivity on highly aligned solid-supported multilamellar lipid membranes. The reflectivity curves have been analyzed by semi-kinematical reflectivity theory modeling the bilayer density profile rho(z). Model simulations of the reflectivity curves cover a large range of vertical momentum transfer q(z), and yield excellent agreement between data and theory. The structural changes observed as a function of the molar peptide/lipid concentration P/L are discussed in a comparative way.

Alamethicin↗
PubMed2006

Laser-guided assembly of heterotypic three-dimensional living cell microarrays.

We have assembled three-dimensional heterotypic networks of living cells in hydrogel without loss of viability using arrays of time-multiplexed, holographic optical traps. The hierarchical control of the cell positions is achieved with, to our knowledge, unprecedented submicron precision, resulting in arrays with an intercell separation <400 nm. In particular, we have assembled networks of Swiss 3T3 fibroblasts surrounded by a ring of bacteria. We have also demonstrated the ability to manipulate hundreds of Pseudomonas aeruginosa simultaneously into two- and three-dimensional arrays with a time-averaged power <2 mW per trap. This is the first time to our knowledge that living cell arrays of such complexity have been synthesized, and it represents a milestone in synthetic biology and tissue engineering.

Biological Assay↗
PubMed2006

Fetal fornix transection and gestation length in sheep.

Experiments in several species indicate that the hippocampus influences hypothalamo-pituitary-adrenal (HPA) axis function. In fetal sheep, simultaneous ACTH and cortisol rises over the last 30 days of gestation peak at term and are necessary for birth. We hypothesized that if the fetal hippocampal formation is functional in late gestation, loss of hippocampal input to the HPA axis following fetal fornix transection would change gestation length in comparison to controls. At 118-121 days of gestation (dG), stereotaxic technique was used in fetal sheep to sham transect (SHAM; n = 8) or transect (FXTX; n = 6) the dorsal fornix at the level of the hippocampal commissure. No differences were found between SHAM and FXTX fetuses in daily hormone profiles over the last week of gestation or in gestation length (148.0 +/- 1.2 vs. 149.0 +/- 0.4 dG, respectively). We conclude that the fetal hippocampus is immature in late gestation and we speculate that an immature hippocampus is necessary for the loss of negative feedback control that gives rise to the long term, simultaneous increases in ACTH and cortisol that are indispensable for labor and delivery at term in sheep.

Acetylcholinesterase↗
PubMed2006

Sex differences in the relationships between BMI, WHR and incidence of cardiovascular disease: a population-based cohort study.

OBJECTIVE: Body mass index (BMI) is associated with increased incidence of cardiovascular disease (CVD). However, the risk could be very different for individuals with the same body mass. The present study explored whether regional fat distribution, as measured by waist-hip ratio (WHR), could modify the impact of BMI on the risk of CVD in men and women. DESIGN: Prospective population-based study. SUBJECTS: A total of 10 369 men and 16 638 women, 45-73 years old, from general population in Malmö, Sweden. MEASUREMENTS: All subjects were followed over 7 years for the incidences of first-ever cardiac event (CE) and ischemic stroke in relation to BMI category (<25.0, 25.0-29.9, > or =30.0) and WHR. RESULTS: The prevalence of overweight and obesity was 39.4 and 13.0%, respectively. During follow-up, 1280 subjects suffered a CVD event (750 CE, 530 ischemic stroke). The risk of CVD in women increased with increasing levels of WHR, irrespective of BMI category. In men, WHR (per 1 s.d. increase) was associated with increased incidence of CVD in those with normal weight (relative risk (RR)=1.24; 95% CI: 1.13-1.37) after adjustments for confounding factors. However, WHR was not related to CVD in overweight men (RR=1.06; 95%CI: 0.94-1.20) or obese men (RR=1.04; 95%CI: 0.87-1.24). A significant interaction was observed between sex and WHR on the CVD risk. CONCLUSION: The effect of WHR on incidence of CVD is modified by the overall body weight and by gender. WHR adds prognostic information on the cardiovascular risk in women at all levels of BMI, and in men with normal weight.

Aged↗
PubMed2006

Co-transplantation of bone marrow stromal cells transduced with IL-7 gene enhances immune reconstitution after allogeneic bone marrow transplantation in mice.

Allogeneic bone marrow transplantation (allo-BMT) is followed by a period of profound immune deficiency, which results in significant susceptibility to infections and limits the extensive application of this approach in clinic. Here, we transduced human interleukin-7 (IL-7) gene into donor-derived bone marrow stromal cells (MSCs) using adenovirus vector, and transplanted this gene-engineered MSCs (MSC-IL-7) into lethally irradiated C57BL/6 mice to investigate their effects on immune reconstitution following allo-BMT. Recipient mice receiving MSC-IL-7 cells plus T-cell-depleted bone marrow cells of BALB/c mice showed a significant increase in thymopoiesis and homeostatic expansion of peripheral T lymphocytes. Furthermore, injection of MSC-IL-7 cells following allo-BMT protected the host from the lethality caused by acute graft-versus-host disease (GVHD) and prevented the occurrence of GVHD induced by transplanted T cells. Thus, the use of MSC-IL-7 cells may be therapeutically useful for enhancing immune reconstitution without aggravating GVHD in allo-BMT mice.

Adenoviridae↗
PubMed2006

Critical interactions between TGF-beta signaling/ELF, and E-cadherin/beta-catenin mediated tumor suppression.

Inactivation of the transforming growth factor-beta (TGF-beta) pathway occurs often in malignancies of the gastrointestinal (GI) system. However, only a fraction of sporadic GI tumors exhibit inactivating mutations in early stages of cancer formation, suggesting that other mechanisms play a critical role in the inactivation of this pathway. Here, we show a wide range of GI tumors, including those of the stomach, liver and colon in elf+/- and elf+/- / Smad4+/- mutant mice. We found that embryonic liver fodrin (ELF), a beta-Spectrin originally identified in endodermal stem/progenitor cells committed to foregut lineage, possesses potent antioncogenic activity and is frequently inactivated in GI cancers. Specifically, E-cadherin accumulation at cell-cell contacts and E-cadherin-beta-catenin-dependent epithelial cell-cell adhesion is disrupted in elf+/- / Smad4+/- mutant gastric epithelial cells, and could be rescued by ectopic expression of full-length elf, but not Smad3 or Smad4. Subcellular fractionation revealed that E-cadherin is expressed mainly at the cell membrane after TGF-beta stimulation. In contrast, elf+/- / Smad4+/- mutant tissues showed abnormal distribution of E-cadherin that could be rescued by overexpression of ELF but not Smad3 or Smad4. Our results identify a group of common lethal malignancies in which inactivation of TGF-beta signaling, which is essential for tumor suppression, is disrupted by inactivation of the ELF adaptor protein.

Animals↗
PubMed2006

Phosphorylation of neurofibromin by PKC is a possible molecular switch in EGF receptor signaling in neural cells.

Children with neurofibromatosis (NF1) typically develop central nervous system (CNS) abnormalities, including aberrant proliferation of astrocytes and formation of benign astrocytomas. The NF1 gene encodes neurofibromin, a Ras-GAP, highly expressed in developing neural cells; the mechanism of regulation of neurofibromin as a Ras-GAP, remains however unknown. We now show that, in response to EGF, neurofibromin is in vivo phosphorylated on serine residues by PKC-alpha, in human, rat, and avian CNS cells and cell lines. EGF-induced PKC phosphorylation was prominent in the cysteine/serine-rich domain (CSRD) of neurofibromin, which lies in the N-terminus and upstream of the Ras-GAP domain (GRD), and this modification significantly increased the association of neurofibromin with actin in co-immunoprecipitations. In addition, we show that Ras activation in response to EGF was significantly lowered when C62B cells overexpressed a construct encoding both CSRD + GRD. Moreover, when PKC-alpha was downregulated, the Ras-GAP activity of CSRD + GRD was significantly diminished, whereas overexpressed GRD alone acted as a weaker GAP and in a PKC-independent manner. Most importantly, functional Ras inhibition and EGF signaling shifts were established at the single cell level in C6-derived cell lines stably overexpressing CSRD + GRD, when transient co-overexpression of Ras and PKC-depletion prior to stimulation with EGF-induced mitosis. Taken together, these data provide the first evidence of a functional, allosteric regulation of GRD by CSRD, which requires neurofibromin phosphorylation by PKC and association with the actin cytoskeleton. Our data may suggest a novel mechanism for regulating biological responses to EGF and provide a new aspect for the understanding of the aberrant proliferation seen in the CNS of children with NF1.

Animals↗
PubMed2006

pKa of the mRNA cap-specific 2'-O-methyltransferase catalytic lysine by HSQC NMR detection of a two-carbon probe.

We have characterized the side chain pKa for a single lysine analogue within a 316-residue protein containing 21 lysines and 1678 carbon atoms at natural isotope abundance. To do this, the single reactive cysteine of a K175C mutant of VP39 (the mRNA cap-specific 2'-O-methyltransferase from vaccinia virus) was modified to S-(beta-aminoethyl)cysteine (gamma-thialysine) using freshly prepared (13C)aziridine at room temperature. Modification was accompanied by the rescue of catalytic function at high specific activity. After the fastidious removal of the noncovalently protein-bound aziridine self-polymer using a novel chelating dialysis procedure, signals were monitored by HSQC NMR. Appropriately pH-shifting HSQC NMR peaks were identified in the (13C)aziridine-modified enzyme, corresponding to detection of the two covalently attached (13C)thioethylamino atoms. The identification was strengthened by comparison with the positions and pH shifts of spectral peaks for tripeptide controls, a small molecule aziridine self-polymer mimetic, and a cysteine-minus control enzyme. pH titration of the modified protein indicated an apparent pKa of 8.5, consistent with a perturbed pKa for the catalytic lysine and a model in which the surrounding charged groups direct the lysine epsilon-amino pKa via both local electrostatic environment and orbital directionality.

Amino Acid Sequence↗
PubMed2006

Immune responses to AAV in a phase I study for Canavan disease.

BACKGROUND: Canavan disease is a rare leukodystrophy with no current treatment. rAAV-ASPA has been developed for gene delivery to the central nervous system (CNS) for Canavan disease. This study represents the first use of a viral vector in an attempt to ameliorate a neurodegenerative disorder. METHODS: Subjects received intracranial infusions via six cranial burr holes. Adeno-associated virus, serotype 2 (AAV2), mediated intraparenchymal delivery of the human aspartoacylase cDNA at a maximum dose of 1 x 10(12) vector genomes per subject. The immune response and safety profiles were monitored in the follow-up of ten subjects. RESULTS: Following rAAV2 administration, we found no evidence of AAV2 neutralizing antibody titers in serum for the majority of subjects tested (7/10). In a subset (3/10) of subjects, low to moderately high levels of AAV2 neutralizing antibody with respect to baseline were detected. In all subjects, there were minimal systemic signs of inflammation or immune stimulation. In subjects with catheter access to the brain lateral ventricle, cerebrospinal fluid was examined and there was a complete absence of neutralizing antibody titers with no overt signs of brain inflammation. CONCLUSIONS: rAAV2 vector administration to the human CNS appears well tolerated. The low levels of immune response to AAV2 detected in 3/10 subjects in this study suggest at this dose and with intraparenchymal administration this approach is relatively safe. Long-term monitoring of subjects and expansion to phase II/III will be necessary in order to make definitive statements on safety and efficacy.

Amidohydrolases↗