Different structure of polytene chromosomes ofPhaseolus coccineus suspensors during early embryogenesis

Summary The pattern of DNA and RNA puffs in pair VII of polytene chromosomes has been investigated in the suspensor ofPhaseolus coccineus during early embryo development. The pattern of³H-TdR and³H-U incorporation has been also detected. Collected data indicate that: 1. both heterochromatic regions, p₁₁ and q_(111+112), of chromosome pair VII, organize large DNA puffs; 2. DNA puffs of both regions are specific of different embryo differentiation steps; 3. a seasonal influence on the DNA puffing seems also to be present, as demonstrated by the comparison of the results collected in two different crops; 4. the incorporation experiment by³H-TdR evidences that not all DNA puffs show clustered labeling; 5. the RNA puffing of the two regions seems also to be specific of determined embryo stages.     

The protein encoded by a growth arrest-specific gene (gas6) is a new member of the vitamin K-dependent proteins related to protein S, a negative coregulator in the blood coagulation cascade.

A set of growth arrest-specific genes (gas) whose expression is negatively regulated after serum induction has previously been described (C. Schneider, R. M. King, and L. Philipson, Cell 54:787-793, 1988). The detailed analysis of one of them, gas6, is reported here, gas6 mRNA (2.6 kb) is abundantly expressed in serum-starved (48 h in 0.5% fetal calf serum) NIH 3T3 cells but decreases dramatically after fetal calf serum or basic fibroblast growth factor stimulation. The human homolog of gas6 was also cloned and sequenced, revealing a high degree of homology and a similar pattern of expression in IMR90 human fibroblasts. Computer analysis of the protein encoded by murine and human gas6 cDNAs showed significant homology (43 and 44% amino acid identity, respectively) to human protein S, a negative coregulator in the blood coagulation pathway. By using an anti-human Gas6 monospecific affinity-purified antibody, we show that the biosynthetic level of human Gas6 fully reflects mRNA expression in IMR90 human fibroblasts. This finding thus defines a new member of vitamin K-dependent proteins that is expressed in many human and mouse tissues and may be involved in the regulation of a protease cascade relevant in growth regulation.     

Thermodynamics of the high-affinity interaction of TCF4 with beta-catenin

The formation of a complex between beta-catenin and members of the TCF/LEF family of high-mobility group proteins is a key regulatory event in the wnt-signaling pathway, essential for embryonal development as well as the growth of normal and malignant colon epithelium. We have characterized the binding of TCF4 to human beta-catenin by steady-state intrinsic fluorescence quenching experiments, surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). Binding studies in solution and in heterogeneous phase showed that TCF4 binds reversibly to beta-catenin with an affinity (KB) of 3(+/-1) 10(8) M(-1). Site-directed mutagenesis, together with calorimetric measurements, revealed that residue D16 in TCF4 plays a crucial role in high-affinity binding. Mutation of this residue to alanine resulted in a decrease of KB by two orders of magnitude as well as a significant reduction in binding enthalpy. Binding of TCF4 to beta-catenin gave rise to a large negative enthalpy change at 25 degrees C (-29.7 kcal/mol). Binding enthalpies were strongly temperature dependent, which resulted in the determination of a large heat capacity change upon binding of -1.5 kcal/(mol K). The molecular events that take place upon complex formation are discussed using the measured thermodynamic data together with the crystal structure of the beta-catenin arm repeat region/TCF complex.     

Hematopoietic growth factors in autologous transplantation

Hematopoietic growth factors (HGFs) sustain the survival, proliferation and differentiation of hematopoietic stem cells and some functions of mature blood cells. In man several HGFs have been characterised and cloned so far, and this has allowed investigators to confer the rationale for the clinical application of these molecules in hematology and oncology. In particular G-CSF and GM-CSF are currently utilised to abrogate the hematological toxicity of chemotherapy for standard and dose-intensified therapy, neutropenia following bone marrow and peripheral blood stem cell transplantation. Moreover there has recently been great interest in the ex vivo expansion of hematopoietic stem and progenitor cells for a variety of applications, such as in vitro tumor cell purging or for reducing the volume of blood processed by the leukapheresis. Several combinations of HGFs have been described to sustain the ex vivo survival and proliferation of these cells disclosing new opportunities in the field of stem cells transplants.     

Comparative analysis of rice MADS-box genes expressed during flower development

MADS-box genes involved in flower development have been isolated and studied in a wide variety of plant species. However, most of these studies are related to dicot species like Antirrhinum majus, Arabidopsis thaliana and Petunia hybrida. Although the floral structures of typical monocot and dicot flowers differ substantially, previous studies indicate that MADS-box genes controlling floral organ identity in dicots can also be identified in monocot plants like rice and maize. To extend this study further to obtain a more global picture of monocot and dicot MADS-box gene evolution, we performed a phylogenetic study using MADS-box genes from A. thaliana and Oryza sativa. Furthermore, we investigated whether the identified orthologues of Arabidopsis and rice have a conserved expression profile that could indicate conservation of function.     

Mycobacterium tuberculosis epitope-specific interferon-g production in healthy Brazilians reactive and non-reactive to tuberculin skin test

The interferon (IFN)-γ response to peptides can be a useful diagnostic marker of Mycobacterium tuberculosis (MTB) latent infection. We identified promiscuous and potentially protective CD4⁺ T-cell epitopes from the most conserved regions of MTB antigenic proteins by scanning the MTB antigenic proteins GroEL2, phosphate-binding protein 1 precursor and 19 kDa antigen with the TEPITOPE algorithm. Seven peptide sequences predicted to bind to multiple human leukocyte antigen (HLA)-DR molecules were synthesised and tested with IFN-γ enzyme-linked immunospot (ELISPOT) assays using peripheral blood mononuclear cells (PBMCs) from 16 Mantoux tuberculin skin test (TST)-positive and 16 TST-negative healthy donors. Eighty-eight percent of TST-positive donors responded to at least one of the peptides, compared to 25% of TST-negative donors. Each individual peptide induced IFN-γ production by PBMCs from at least 31% of the TST-positive donors. The magnitude of the response against all peptides was 182 ± 230 x 10⁶ IFN-γ spot forming cells (SFC) among TST-positive donors and 36 ± 62 x 10⁶ SFC among TST-negative donors (p = 0.007). The response to GroEL2 (463-477) was only observed in the TST-positive group. This combination of novel MTB CD4 T-cell epitopes should be tested in a larger cohort of individuals with latent tuberculosis (TB) to evaluate its potential to diagnose latent TB and it may be included in ELISPOT-based IFN-γ assays to identify individuals with this condition.     

M-07e human leukemic factor-dependent cell line provides a rapid and sensitive bioassay for the human cytokines GM-CSF and IL-3

We have isolated a subline of the M-07 human megakaryoblastic leukemia cell line, designated M-07e, that requires either interleukin-3 (IL-3) or granulocyte macrophage colony-stimulating factor (GM-CSF) for growth, even in the presence of fetal calf serum. This cell line will not grow long term in any other cytokine although it responds slightly to IL-2, IL-4, IL-6, IL-9, and interferon-gamma. We have used the M-07e subline to develop a quantitative bioassay for the measurement of levels of either GM-CSF or IL-3. This assay is as sensitive to either factor as the human bone marrow colony assay (CFU-GM) or the chronic myelogeneous leukemic (CML) blast cell proliferation assay for these factors and is much more convenient and reliable than either. With this assay, as little as 25-50 pg/ml of either IL-3 or GM-CSF can be detected, a level that should render the assay useful for analysis of these molecules in samples from patients undergoing colony-stimulating factor therapy and from conditioned media from natural sources of the factors. In these cases, neutralizing antisera to each cytokine are required to demonstrate the specificity of the assay. This assay, in combination with quantitative immunoassays, should greatly facilitate the analysis of the roles of IL-3 and GM-CSF in regulating hematopoiesis both in patients and in natural sources of the cytokines.