A codon window in mRNA downstream of the initiation codon where NGG codons give strongly reduced gene expression in Escherichia coli

The influences on gene expression by codons at positions +2, +3, +5 and +7 downstream of the initiation codon have been compared. Most of the +2 codons that are known to give low gene expression are associated with a higher expression if placed at the later positions. The NGG codons AGG, CGG, UGG and GGG, but not GGN or GNG (where N is non-G), are unique since they are associated with a very low gene expression also if located at positions +2, +3 and +5. All codons, including NGG, give a normal gene expression if placed at positions +7. The negative effect by the NGG codons is true for both the lacZ and 3A′ model genes. The low expression is suggested to originate at the translational level, although it is not the result of mRNA secondary structure or a lowered intracellular mRNA pool.     

Formation and hydrolysis of triacylglycerol and sterols epoxides: role of unsaturated triacylglycerol peroxyl radicals

Epoxidation of unsaturated pure triacylglycerols (TAGs), cholesterol, and phytosterols was investigated using air and 18O2 oxidation experiments. Oxidized lipids were analyzed using both triple quadrupole mass spectrometry (MS), ion-trap MS in the direct infusion mode, and triple quadrupole MS in tandem with a liquid chromatograph (LC-MS/MS). Pure 1,2-distearoyl-3-oleoyl-glycerol (SSO) samples were heated in sealed vials under air or 18O2 atmosphere at 160 degrees C for 1 h. LC-MS/MS analysis of 18O-labeled oxidized TAGs revealed that hydroperoxides and epoxide TAGs are formed mainly during this first step. Then, oxidized TAGs were incubated under an inert atmosphere, separately with 1,2-dipalmitoyl-3-oleoyl-glycerol (PPO) at 160 degrees C for 90 min, and with cholesterol and stigmasterol at 100 degrees C for 10 min. Subsequent LC-MS/MS analysis revealed the occurrence of epoxidation products of PPO, cholesterol, and sitosterol. Therefore, we showed the epoxidation of unsaturated lipids proceeds readily in contact with hydroperoxide TAGs, in the absence of molecular oxygen. Dual oxidation experiments using both air and 18O2 allowed investigation of oxygen atom transfer during epoxidation of lipids. Moreover, the experimental oxidation design presented can be used to study fragmentation pathways, as illustrated for 5,6-epoxycholesterol (CE) on both triple quadrupole and ion-trap MS. We report for the first time the occurrence of 5,6;22,23-diepoxystigmasterol (StDE) and 5,6;22,23-diepoxybrassicasterol (BDE) in autoxidized vegetable oils. Additionally, acid-catalyzed hydrolysis of epoxidized lipids, with emphasis on phytosterol polyol formation, was investigated using a model gastric medium. For confirmation, almost all identified products were synthesized and characterized by MS.     

Differential requirements for Smad4 in TGFbeta-dependent patterning of the early mouse embryo

Genetic and biochemical data have identified Smad4 as a key intracellular effector of the transforming growth factor beta (TGFbeta superfamily of secreted ligands. In mouse, Smad4-null embryos do not gastrulate, a phenotype consistent with loss of other TGFbeta-related signaling components. Chimeric analysis reveals a primary requirement for Smad4 in the extra-embryonic lineages; however, within the embryo proper, characterization of the specific roles of Smad4 during gastrulation and lineage specification remains limited. We have employed a Smad4 conditional allele to specifically inactivate the Smad4 gene in the early mouse epiblast. Loss of Smad4 in this tissue results in a profound failure to pattern derivatives of the anterior primitive streak, such as prechordal plate, node, notochord and definitive endoderm. In contrast to these focal defects, many well-characterized TGFbeta- and Bmp-regulated processes involved in mesoderm formation and patterning are surprisingly unaffected. Mutant embryos form abundant extra-embryonic mesoderm, including allantois, a rudimentary heart and middle primitive streak derivatives such as somites and lateral plate mesoderm. Thus, loss of Smad4 in the epiblast results not in global developmental abnormalities but instead in restricted patterning defects. These results suggest that Smad4 potentiates a subset of TGFbeta-related signals during early embryonic development, but is dispensable for others.     

The Lim homeobox gene Lhx2 is required for olfactory sensory neuron identity

Progenitor cells in the mouse olfactory epithelium generate over a thousand subpopulations of neurons, each expressing a unique odorant receptor (OR) gene. This event is under the control of spatial cues, since neurons in different epithelial regions are restricted to express region-specific subsets of OR genes. We show that progenitors and neurons express the LIM-homeobox gene Lhx2 and that neurons in Lhx2-null mutant embryos do not diversify into subpopulations expressing different OR genes and other region-restricted genes such as Nqo1 and Ncam2. Lhx2-/- embryos have, however, a normal distribution of Mash1-positive and neurogenin 1-positive neuronal progenitors that leave the cell cycle, acquire pan-neuronal traits and form axon bundles. Increased cell death in combination with increased expression of the early differentiation marker Neurod1, as well as reduced expression of late differentiation markers (Galphaolf and Omp), suggests that neuronal differentiation in the absence of Lhx2 is primarily inhibited at, or immediate prior to, onset of OR expression. Aberrant regional expression of early and late differentiation markers, taken together with unaltered region-restricted expression of the Msx1 homeobox gene in the progenitor cell layer of Lhx2-/- embryos, shows that Lhx2 function is not required for all aspects of regional specification of progenitors and neurons. Thus, these results indicate that a cell-autonomous function of Lhx2 is required for differentiation of progenitors into a heterogeneous population of individually and regionally specified mature olfactory sensory neurons.     

TGFbeta superfamily signals are required for morphogenesis of the kidney mesenchyme progenitor population

The TGFbeta superfamily plays diverse and essential roles in kidney development. Gdf11 and Bmp4 are essential for outgrowth and positioning of the ureteric bud, the inducer of metanephric mesenchyme. During nephrogenesis, Bmp7 is required for renewal of the mesenchyme progenitor population. Additionally, in vitro studies demonstrate inhibitory effects of BMPs and TGFbetas on collecting duct branching and growth. Here, we explore the predicted models of TGFbeta superfamily function by cell-specific inactivation of Smad4, a key mediator of TGFbeta signaling. Using a HoxB7cre transgene expressed in ureteric bud and collecting duct, we find that development of the collecting duct is Smad4 independent. By contrast, removal of Smad4 in nephrogenic mesenchyme using the Bmp7(cre/+) allele leads to disorganization of the nephrogenic mesenchyme and impairment of mesenchyme induction. Smad4-deficient metanephric mesenchyme does not display defects in inducibility in LiCl or spinal cord induction assays. However, in situ hybridization and lineage analysis of Smad4 null mesenchyme cells at E11.5 show that the nephrogenic mesenchyme does not aggregate tightly around the ureteric bud tips, but remains loosely associated, embedded within a population of cells expressing markers of both nephrogenic mesenchyme and peripheral stroma. We conclude that the failure of recruitment of nephrogenic mesenchyme leaves a primitive population of mesenchyme at the periphery of the kidney. This population is gradually depleted, and by E16.5 the periphery is composed of cells of stromal phenotype. This study uncovers a novel role for TGFbeta superfamily signaling in the recruitment and/or organization of the nephrogenic mesenchyme at early time-points of kidney development. Additionally, we present conclusive genetic lineage mapping of the collecting duct and nephrogenic mesenchyme.     

Stanniocalcin in terminally differentiated mammalian cells

Stanniocalcin (STC) is a glycoprotein hormone originally found in teleost fish, where it regulates the calcium/phosphate homeostasis, and protects the fish against toxic hypercalcemia. STC was considered an exclusive fish protein, until the cloning of cDNA for human (in 1995) and murine (in 1996) STC. We originally reported a high constitutive content of STC in mammalian brain neurons, and found that the expression of STC occurred concomitantly with terminal differentiation of neural cells. Since then, we have investigated the expression of STC in relation to terminal cell differentiation also in mammalian hematopoietic tissue, and fat tissues. In this review we summarize our findings on STC expression during postmitotic differentiation in three different cell systems; in neural cells, in megakaryocytes and in adipocytes. We also present findings, suggesting that STC plays a role for maintaining the integrity of terminally differentiated mammalian cells.     

Intercellular metabolic compartmentation in the brain: past, present and future

The first indication of 'metabolic compartmentation' in brain was the demonstration that glutamine after intracisternal [14C]glutamate administration is formed from a compartment of the glutamate pool that comprises at most one-fifth of the total glutamate content in the brain. This pool, which was designated 'the small compartment,' is now known to be made up predominantly or exclusively of astrocytes, which accumulate glutamate avidly and express glutamine synthetase activity, whereas this enzyme is absent from neurons, which eventually were established to constitute 'the large compartment.' During the following decades, the metabolic compartment concept was refined, aided by emerging studies of energy metabolism and glutamate uptake in cellularly homogenous preparations and by the histochemical observations that the two key enzymes glutamine synthetase and pyruvate carboxylase are active in astrocytes but absent in neurons. It is, however, only during the last few years that nuclear magnetic resonance (NMR) spectroscopy, assisted by previously obtained knowledge of metabolic pathways, has allowed accurate determination in the human brain in situ of actual metabolic fluxes through the neuronal tricarboxylic acid (TCA) cycle, the glial, presumably mainly astrocytic, TCA cycle, pyruvate carboxylation, and the 'glutamate-glutamine cycle,' connecting neuronal and astrocytic metabolism. Astrocytes account for 20% of oxidative metabolism of glucose in the human brain cortex and accumulate the bulk of neuronally released transmitter glutamate, part of which is rapidly converted to glutamine and returned to neurons in the glutamate-glutamine cycle. However, one-third of released transmitter glutamate is replaced by de novo synthesis of glutamate from glucose in astrocytes, suggesting that at steady state a corresponding amount of glutamate is oxidatively degraded. Net degradation of glutamate may not always equal its net production from glucose and enhanced glutamatergic activity, occurring during different types of cerebral stimulation, including the establishment of memory, may be associated with increased de novo synthesis of glutamate. This process may contribute to a larger increase in glucose utilization rate than in rate of oxygen consumption during brain activation. The energy yield in astrocytes from glutamate formation is strongly dependent upon the fate of the generated glutamate.     

Frequency analysis of atrial fibrillation from the surface electrocardiogram

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. Neither the natural history of AF nor its response to therapy are sufficiently predictable by clinical and echocardiographic parameters. Atrial fibrillatory frequency (or rate) can reliably be assessed from the surface electrocardiogram (ECG) using digital signal processing (filtering, subtraction of averaged QRST complexes, and power spectral analysis) and shows large inter-individual variability. This measurement correlates well with intraatrial cycle length, a parameter which appears to have primary importance in AF domestication and response to therapy. AF with a low fibrillatory rate is more likely to terminate spontaneously, and responds better to antiarrhythmic drugs or cardioversion while high rate AF is more often persistent and refractory to therapy. In conclusion, frequency analysis of AF seems to be useful for non-invasive assessment of electrical remodeling in AF and may subsequently be helpful for guiding AF therapy.     

Characterization of low-glycosylated forms of soluble human urokinase receptor expressed in Drosophila Schneider 2 cells after deletion of glycosylation-sites

The urokinase-type plasminogen activator receptor (uPAR) is a glycolipid-anchored membrane protein that is thought to play an active role during cancer cell invasion and metastasis. We have expressed a truncated soluble form of human uPAR using its native signal peptide in stably transfected Drosophila Schneider 2 (S2) cells. This recombinant product, denoted suPAR (residues 1–283), is secreted in high quantities in serum-free medium and can be isolated in very high purity. Characterization by SDS–PAGE and mass spectrometry reveals that suPAR produced in this system carries a uniform glycosylation composed of biantennary carbohydrates. In contrast, suPAR produced in stably transfected Chinese hamster ovary (CHO) cells carries predominantly complex-type glycosylation and exhibits in addition a site-specific microheterogeneity of the individual N-linked carbohydrates. Measurement of binding kinetics for the interaction with uPA by surface plasmon resonance reveals that S2-produced suPAR exhibits binding properties similar to those of suPAR produced by CHO cells. By site-directed mutagenesis we have furthermore removed the five potential N-linked glycosylation-sites either individually or in various combinations and studied the effect thereof on secretion and ligand-binding. Only suPAR completely deprived of N-linked glycosylation exhibits an impaired level of secretion. All the other mutants showed comparable secretion levels and retained the ligand-binding properties of suPAR-wt. In conclusion, stable expression of suPAR in Drosophila S2 cells offers a convenient and attractive method for the large scale production of homogeneous preparations of several uPAR mutants, which may be required for future attempts to solve the three-dimensional structure of uPAR by X-ray crystallography.     

Bcl-2 expression in metastatic malignant melanoma. Importance for the therapeutic efficacy of biochemotherapy

For the majority of patients with metastatic malignant melanoma the prognosis is poor. Immunotherapy and biochemotherapy have shown promise with a subset of durable responses, but there is still a great need for a better understanding of the mechanisms of action during treatment to optimize future treatment schedules. In the present study Bcl-2 expression was studied in biopsies from ten patients with metastatic malignant melanoma (five with regional disease and five with systemic disease) treated with biochemotherapy (cisplatinum 30 mg/m2 days 1-3, DTIC 250 mg/m2 days 1-3 i.v. and Interferon-alpha2b 10 MIU s.c. 3 days a week, on a 28-day cycle). The expression of Bcl-2 by the tumour cells was separately recorded in areas of histopathological regressive changes and in areas of unaffected tumour growth. Comparisons were made with biopsies from 14 untreated patients. In 10 of 10 treated patients a high expression of Bcl-2 by the tumour cells was found in areas of unaffected tumour growth. In contrast, only in 5 of 13 untreated patients was a high expression of Bcl-2 by the tumour cells found in these areas ( P=0.008). A significant difference was also found in the expression of Bcl-2 by the tumour cells between areas of unaffected tumour growth and areas of histopathological regressive changes ( P=0.03). The significantly higher expression of Bcl-2 by the tumour cells in areas of unaffected tumour growth in treated patients compared to untreated patients indicates that clones with a high expression of Bcl-2 may be present after therapy, preventing apoptosis and eventually in many patients resulting in progressive disease. Supporting this concept, a difference was also found between the expression of Bcl-2 in areas of unaffected tumour growth, i.e. in areas of treatment failure, and the expression in areas of histopathological regressive changes. Thus immunohistochemical analysis of tumour biopsies shortly after therapy seems to be a good surrogate endpoint that allows a detailed analysis of Bcl-2 expression. The high expression of Bcl-2 shown in unaffected tumour areas after therapy suggests the need for additional treatment, e.g. Bcl-2 antisense therapy.