Numerical simulation of dendrite growth during solidification

A comprehensive probabilistic model for simulating dendrite morphology and investigating dendritic growth kinetics during solidification has been developed, based on a modified Cellular Automaton (mCA) for microscopic modeling of nucleation, growth of crystals and solute diffusion. The mCA model numerically calculated solute redistribution both in the solid and liquid phases, the curvature of dendrite tips and the growth anisotropy. This modeling takes account of thermal, curvature and solute diffusion effects. Therefore, it can simulate microstructure formation both on the scale of the dendrite tip length. This model was then applied for simulating dendritic solidification of an Al-7%Si alloy. Both directional and equiaxed dendritic growth has been performed to investigate the growth anisotropy and cooling rate on dendrite morphology. Furthermore, the competitive growth and selection of dendritic crystals have also investigated.

DNA binding-independent transcriptional activation of the vascular endothelial growth factor gene (VEGF) by the Myb oncoprotein

Myb is a key transcription factor that can regulate proliferation, differentiation, and apoptosis, predominantly in the haemopoietic system. Abnormal expression of Myb is associated with a number of cancers, both haemopoietic and non-haemopoietic. In order to better understand the role of Myb in normal and tumorigenic processes, we undertook a cDNA array screen to identify genes that are regulated by this factor. In this way, we identified the gene encoding vascular endothelial growth factor (VEGF) as being potentially regulated by the Myb oncoprotein in myeloid cells. To determine whether this was a direct effect on VEGF gene transcription, we examined the activity of the murine VEGF promoter in the presence of either wild-type (WT) or mutant forms of Myb. It was found that WT Myb was able to activate the VEGF promoter and that a minimal promoter region of 120 bp was sufficient to confer Myb responsiveness. Surprisingly, activation of the VEGF promoter was independent of DNA binding by Myb. This was shown by the use of DNA binding-defective Myb mutants and by mutagenesis of a potential Myb-binding site in the minimal promoter. Mutation of Sp1 sites within this region abolished Myb-mediated regulation of a reporter construct, suggesting that Myb DNA binding-independent activation of VEGF expression occurs via these Sp1 binding elements. Regulation of VEGF production by Myb has implications for the potential role of Myb in myeloid leukaemias and in solid tumours where VEGF may be functioning as an autocrine growth factor. (c) 2006 Elsevier Inc. All rights reserved.

Super-CHO - A cell line capable of autocrine growth under fully defined protein-free conditions

Chinese Hamster Ovary (CHO) cells are widely used for the large scale production of recombinant biopharmaceuticals. Growth of the CHO-K1 cell line has been demonstrated in serum-free medium containing insulin, transferrin and selenium. In an attempt to get autocrine growth in protein-free medium, DNA coding for insulin and transferrin production was transfected into CHO-K1 cells. Transferrin was expressed well, with clones secreting approximately 1000 ng/10(6)cells/24h. Insulin was poorly expressed, with rates peaking at 5 ng/10(6)cells/24h. Characterisation of the secreted insulin indicated that the CHO cells were incompletely processing the insulin molecule. Site-directed mutagenesis was used to introduce a furin (prohormone converting enzyme) recognition sequence into the insulin molecule, allowing the production of active insulin. However, the levels were still too low to support autocrine growth. Further investigations revealed insulin degrading activity (presumably due to the presence of insulin degrading enzymes) in the cytoplasm of CHO cells. To overcome these problems insulin-like growth factor I (instead of insulin) was transfected into the cells. IGF-1 was completely processed and expressed at rates greater than 500 ng/10(6)cells/24h. In this paper we report autonomous growth of the transfected CHO-K1 cell line expressing transferrin and IGF-1 in protein-free medium without the addition of exogenous growth factors. Growth rates and final cell densities of these cells were identical to that of the parent cell line CHO-K1 growing in insulin, transferrin, and selenium supplemented serum-free media.

Identification and characterization of a G protein-coupled receptor homolog encoded by murine cytomegalovirus

This report describes the identification of a murine cytomegalovirus (MCMV) G protein-coupled receptor (GCR) homolog. This open reading frame (M33) is most closely related to, and collinear with, human cytomegalovirus UL33, and homologs are also present in human herpesvirus 6 and 7 (U12 for both viruses). Conserved counterparts in the sequenced alpha- or gammaherpesviruses have not been identified to date, suggesting that these genes encode proteins which are important for the biological characteristics of betaherpesviruses. We have detected transcripts for both UL33 and M33 as early as 3 or 4 h postinfection, and these reappear at late times. In addition, we have identified N-terminal splicing for both the UL33 and M33 RNA transcripts. For both open reading frames, splicing results in the introduction of amino acids which are highly conserved among known GCRs. To characterise the function of the M33 in the natural host, two independent MCMV recombinant viruses were prepared, each of which possesses an M33 open reading frame which has been disrupted with the beta-galactosidase gene. While the recombinant M33 null viruses showed no phenotypic differences in replication from wild-type MCMV in primary mouse embryo fibroblasts in vitro, they showed severely restricted growth in the salivary glands of infected mice. These data suggest that M33 plays an important role in vivo, in particular in the dissemination to or replication in the salivary gland, and provide the first evidence for the function of a viral GCR homolog in vivo.

Role of galectin-1 in the olfactory nervous system

The olfactory nervous system is responsible for the detection of odors. Primary sensory olfactory neurons are located in a neuroepithelial sheet lining the nasal cavity. The axons from these neurons converge on to discrete loci or glomeruli in the olfactory bulb. Each glomerulus consists of the termination of thousands of primary axons on the dendrites of second-order olfactory neurons. What are the molecular mechanisms which guide growing olfactory axons to select sites in the olfactory bulb? We have shown that subpopulations of these axons differentially express cell surface carbohydrates and that these different subpopulations target and terminate in particular regions of the olfactory bulb. Interestingly, the olfactory neurons and glial components in the olfactory pathway between the nose and brain express galectin-1. By using in vitro assays of neurite outgrowth we found that both galectin-1 and it's ligands were capable of specifically stimulating neurite elongation. Examination of the olfactory system in galectin-1 null mutants revealed that a subpopulation of axons failed to navigate to their target site in the olfactory bulb. This is the first phenotypic effect observed in galectin-1 null mutants and indicates that galectin-1 has a role in the growth and/or guidance of a subpopulation of axons in the olfactory system during development.

Chinese hamster ovary cells produce sufficient recombinant insulin-like growth factor I to support growth in serum-free medium - Serum-free growth of IGF-I producing CHO cells

Insulin-like growth factor I has similar mitogenic effects to insulin, a growth factor required by most cells in culture, and it can replace insulin in serum-free formulations for some cells. Chinese Hamster Ovary cells grow well in serum-free medium with insulin and transferrin as the only exogenous growth factors. An alternative approach to addition of exogenous growth factors to serum-free medium is transfection of host cells with growth factor-encoding genes, permitting autocrine growth. Taking this approach, we constructed an IGF-I heterologous gene driven by the cytomegalovirus promoter, introduced it into Chinese Hamster Ovary cells and examined the growth characteristics of Insulin-like growth factor I-expressing clonal cells in the absence of the exogenous factor. The transfected cells secreted up to 500 ng/10(6) cells/day of mature Insulin-like growth factor I into the conditioned medium and as a result they grew autonomously in serum-free medium containing transferrin as the only added growth factor. This growth-stimulating effect, observed under both small and large scale culture conditions, was maximal since no further improvement was observed in the presence of exogenous insulin.

Prepartum supplementation effects on growth and fertility in Bos indicus-cross cows

Three experiments were conducted in the dry tropics of north Australia using Bos indicus-cross cows. Cows in mid-late pregnancy were either unsupplemented during the late dry season or offered ad libitum (2 kg/day) molasses with 7.4% urea (w/w) (M8U) or cottonseed meal (1 kg/day) for up to 54 days commencing 2 months before the start of the calving season. Supplementation reduced weight loss in experiments 1 and 2 (P

Functional growth hormone (GH) receptors and GH are expressed by preimplantation mouse embryos: A role for GN in early embryogenesis?

The results of this study challenge the widely held view that growth hormone (GH) acts only during the postnatal period. RNA phenotyping shows transcripts for the GH receptor and GH-binding protein in mouse preimplantation embryos of all stages from fertilized eggs (day 1) to blastocysts (day 4). An antibody specific to the cytoplasmic region of the GH receptor revealed receptor protein expression, first in two-cell embryos, the stage of activation of the embryonic genome (day 2), and in all subsequent stages, In cleavage-stage embryos this immunoreactivity was localized mainly to the nucleus, but clear evidence of membrane labeling was apparent in blastocysts. GH receptor immunoreactivity was also observed in cumulus cells associated with unfertilized oocytes but not in the unfertilized oocytes. The blastocyst receptor was demonstrated to be functional, exhibiting the classic bell-shaped dose-response curves for GH stimulation of both 3-O-methyl glucose transport and protein synthesis. Maximal stimulation of 40-50% was seen for both responses at less than 1 ng/ml recombinant GH, suggesting a role for maternal GK. However mRNA transcripts for GH were also detected from the morula stage (day 3) by using reverse transcription-PCR, and GH immunoreactivity was seen in blastocysts. These observations raise the possibility of a paracrine/autocrine GH loop regulating embryonic development in its earliest stages.

Growth hormone-binding protein in normal and pathologic gestation: Correlations with maternal diabetes and fetal growth

To date, measurements of GH-binding protein (GHBP) during human pregnancy have been carried out using;assays susceptible to interference by the elevated levels of human placental GH typical of late gestation. We recruited a large cohort of pregnant women (n = 140) for serial measurements of GHBP and used the ligand immunofunctional assay for GHBP. For normal gravidas, GHBP levels fell throughout gestation. Mean levels were 1.07 nmol/L (SE = 0.18) in the first trimester, 0.90 nmol/L (SE = 0.08) at 18-20 weeks, 0.73 nmol/L (SE = 0.05) at 28-30 weeks, and 0.62 nmol/L (SE = 0.06) at 36-38 weeks. GHBP levels in the first trimester correlated significantly with maternal body mass index (r = 0.58; P < 0.01). GHBP levels in pregnancies complicated by noninsulin-dependent diabetes mellitus (NIDDM) were substantially elevated at all gestational ages. The mean value in the first quarter (2.29 nmol/L) was more than double the normal mean (P < 0.01). In contrast, patients with insulin-dependent diabetes mellitus (IDDM) showed reduced GHBP concentrations at 36-38 weeks. The correlation between body mass index and GHBP is consistent with a metabolic role for GHBP during pregnancy, as is the dramatic elevation in GHBP observed in cases of NIDDM. At 36 weeks gestation, GHBP was significantly elevated (P < 0.01) in those women whose neonates had low birth weight (

Presence of novel N-CAM glycoforms in the rat olfactory system

The functional activity of the neural cell adhesion molecule N-CAM can be modulated by posttranslational modifications such as glycosylation. For instance, the long polysialic acid side chains of N-CAM alter the adhesion properties of the protein backbone. In the present study, we identified two novel carbohydrates present on N-CAM, NOC-3 and NOC-4. Both carbohydrates were detected on N-CAM glycoforms expressed by subpopulations of primary sensory olfactory neurons in the rat olfactory system. Based on the expression of NOC-3 and NOC-4 and the olfactory marker protein (OMP), four independent subpopulations of primary sensory olfactory neurons were characterized. These neurons expressed: both NOC-3 and NOC-4 but not OMP; both NOC-4 and OMP but not NOC-3; NOC-3, NOC-4, and OMP together; and OMP alone. The NOC-3- and NOC-4-expressing neurons were widely dispersed in the olfactory neuroepithelium lining the nasal cavity. The axons of NOC-4 expressing neurons innervated all glomeruli in the olfactory bulb, whereas the NOC-3 expressing axons terminated in a discrete subset of glomeruli scattered throughout the whole olfactory bulb. We propose that both NOC-3 and NOC-4 are part of a chemical code of olfactory neurons which is used in establishing the topography of connections between the olfactory neuroepithelium and the olfactory bulb. (C) 1997 John Wiley & Sons, Inc.

Effect of specific leaf nitrogen on radiation use efficiency and growth of sunflower

Specific leaf nitrogen (SLN, g/m(2)) is known to affect radiation use efficiency (RUE, g/MJ) in different crops, However, this association and importance have not been well established over a range of different nitrogen regimes for held-grown sunflower (Helianthus annuus L.). An experiment was conducted to investigate different combinations and rates of applied nitrogen on SLN, RUE, and growth of sunflower, A fully irrigated crop was sown on an alluvial-prairie soil (Fluventic Haplustoll) and treated with five combinations of applied nitrogen, Greater nitrogen increased biomass, grain number, and yield, but did not affect harvest index energy-corrected for oil (0.4) or canopy extinction coefficient (0.88), Decreases in biomass accumulation under low nitrogen treatments were associated,vith reductions in leaf area index (LAI) and light interception, When SLN and RUE were examined together, both were less in the anthesis to physiological maturity period, but relatively stable between bud visible and anthesis, However, the effects of canopy SLN on RUE were confounded by high SLN in the top of the canopy and the crop maintaining SLN by reducing LAI, Measurements of leaf CO2 assimilation and theoretical analyses of RUE supported that RUE was related to SLN, The major effect of nitrogen on early growth of sunflower was mediated by leaf area and the distribution of SLN in the canopy rather than direct effects of canopy SLN on RUE alone. Greater responses of RUE to SLN are more evident later in growth, and may be related to the demand of nitrogen by the grain.