The use of transgenic mice in the investigation of transmissible spongiform encephalopathies

The prion, the transmissible agent that causes spongiform encephalopathies such as scrapie, bovine spongiform encephalopathy and Creutzfeldt-Jakob disease, is believed to be devoid of nucleic acid and to be identical to PrPSc (prion protein: scrapie form), a modified form of the normal host protein PrPC (prion protein: cellular form) which is encoded by the single copy gene Prnp. The 'protein only' hypothesis proposes that PrPSc, when introduced into a normal host, causes the conversion of PrPC into PrPSc; it therefore predicts that an animal devoid of PrPC should be resistant to prion diseases. The authors generated homozygous Prnp(o/o) ('PrP knockout') mice and showed that, after inoculation with prions, these mice remained free from scrapie for at least two years while wild-type controls all died within six months. There was no propagation of prions in the Prnp(o/o) animals. Surprisingly, heterozygous Prnp(o/+) mice, which express PrPC at about half the normal level, also showed enhanced resistance to scrapie despite high levels of infectious agent and PrPSc in the brain at an early stage. After introduction of murine PrP transgenes, Prnp(o/o) mice became highly susceptible to mouse--but not to hamster--prions, while the insertion of Syrian hamster PrP transgenes rendered the mice susceptible to hamster prions but much less susceptible to mouse prions. These complementation experiments enabled the application of reverse genetics. The authors prepared animals transgenic for genes encoding PrP with amino terminal deletions of various lengths and found that PrP that lacks 48 amino proximal amino acids (which comprise four of the five octa repeats of PrP) is still biologically active.

Oxygen-dependent regulation of the expression of the catalase gene katA of Lactobacillus sakei LTH677

The catalase gene katA of Lactobacillus sakei LTH677 was cloned and expressed in Escherichia coli UM2, Lactobacillus casei LK1, and Lactobacillus curvatus LTH1432. The last host is a catalase-deficient plasmid-cured derivative of a starter organism used in meat fermentation. The regulation of katA expression was found to be the same in L. sakei LTH677 and the recombinant strains. The addition of H2O2 to anaerobic cultures, as well as a switch to aerobic conditions, resulted in a strong increase in KatA activity. The expression was investigated in more detail with L. sakei LTH677 and L. curvatus LTH4002. The recombinant strain LTH4002 did not accumulate H2O2 under glucose-limited aerobic conditions and remained viable in the stationary phase. Under inductive conditions, the katA-specific mRNA and the apoenzyme were synthesized de novo. Deletion derivatives of the katA promoter were produced, and the regulatory response was investigated by fusion to the beta-glucuronidase reporter gene gusA and expression in L. sakei LTH677. The fact that gene expression was subject to induction was confirmed at the level of transcription and protein synthesis. A small putative regulatory sequence of at least 25 bp was identified located upstream of the -35 site. Competition experiments performed with L. sakei LTH677 harboring the fusion constructs consisting of the katA promoter and gusA revealed that an activator protein is involved in the transcriptional induction of katA.

Inotropic response of stunned hypertrophied myocardium: responsiveness of hypertrophied and normal postischemic isolated rat hearts to calcium and dopamine stimulation

OBJECTIVE

Severely hypertrophied myocardium was described to have a reduced tolerance towards ischemia. For non-hypertrophied hearts inconclusive findings on the Ca(2+)-responsiveness are reported. Information sensitivity to reversible ischemia and on postischemic Ca(2+)-responsiveness of hearts with clinically common moderate hypertrophy is lacking. Thus, the responsiveness of hypertrophied and normal postischemic myocardium to positive inotropic stimulation should be investigated in the present study.

METHODS AND RESULTS

Hearts from spontaneously hypertensive rats (SHR, 4 months old) with significant LV-hypertrophy (+ 50%) and hearts from normotensive 4 months old Wistar rats were investigated using an isovolumic beating isolated heart model (8 hearts/each of the 8 groups). Functional recovery after 30 min of no-flow ischemia was 78 +/- 1% and 77 +/- 3% of preischemic control data in hypertrophied and non-hypertrophied hearts assessed as developed left ventricular pressure (non-ischemic controls: 95 +/- 2% in hypertrophied and 93 +/- 3% in non-hypertrophied controls). Maximum short-term stimulation with Ca2+ revealed a decreased peak left ventricular pressure of 124 +/- 4% in hypertrophied and 120 +/- 5% in non-hypertrophied postischemic hearts, as compared with non-ischemic controls 138 +/- 3% and 157 +/- 5%, respectively ( p < 0.01). A maximum dose of dopamine stimulated hypertrophied and non-hypertrophied postischemic hearts comparable to Ca2+. Analysing the dose-response curve for Ca(2+)-stimulation, the sensitivity expressed as fraction of the maximum was identical in non-ischemic and postischemic myocardium of hypertrophied and non-hypertrophied ventricles in spite of the reduced peak values.

CONCLUSION

The findings demonstrate that after moderate reversible ischemia the steady-state function is similarly decreased in hypertrophied and non-hypertrophied postischemic myocardium. The maximum response to Ca2+ is significantly reduced in both types of myocardium, while the Ca2+ sensitivity is unchanged. Identical results after maximum dopamine stimulation as after Ca2+ indicate that the releasibility of Ca2+ and the beta-adrenoceptors are not the critical causes for the postischemic dysfunction in hypertrophied or non-hypertrophied myocardium.

[Normal accommodative convergence excess--long-term follow-up of conservative therapy with bifocal eyeglasses]

BACKGROUND

In patients with normaccommodative convergence excess it is possible to reduce or eliminate the excess of accommodative convergence by adding plus lenses. The resulting reduction of near deviation can lead to an improvement in the quality of binocular vision at near, and also to a better compensation of an esophoria at near. The aim of the paper was to study long term results in patients with small angle esotropia and esophoria and accommodative convergence excess treated by bifocals.

METHODS

Clinical data of 91 patients were analysed retrospectively. Among them were 13 patients with esophoria, 32 patients with microesotropia and 46 with microesotropia and a phoric component. An orthoptic status was performed every three months and at every examination it was tried to reduce the added plus lenses. The mean follow up was 5.6 +/- 2.4 years (range: 1.1-13.2).

RESULTS

The mean onset of strabismus was similar in all groups: i.e. 2.5 (+/- 1.7) years. The patients received their first bifocals on average 3.4 (+/- 1.9) years later. In 40 of the 91 patients the near addition could be stopped because of sufficient decrease of accommodative convergence excess during the follow-up period. The convergence excess decreased continuously in all patients with esophoria and microesotropia and the additional plus lenses could be stopped on average after 6.4 (3.5-8.4) years (esophoria) and 5.0 (2.6-8.1) years (microesotropia) respectively. In patients with microesotropia and an additional phoric deviation bifocals were only partly successful to reduce the convergence excess. The basic angle decompensated in more than half of the patients (27 out of 46) and was operated in 14 cases by unilateral resection/recession procedure. After the operation the convergence excess decreased rapidly and the bifocals could be stopped after 4.4 (3.4-7.4) years. In the remaining 19 cases it was possible to reduced the convergence excess with bifocals in 8 patients after about 8.1 (4.1-9.3) years and in some of the remaining 11 cases a Fadenoperation has been suggested.

CONCLUSION

While wearing bifocals the accommodative convergence excess decreased completely in patients with esophoria and microesotropia. In the condition with markedly reduced binocular vision and a large phoric component at far and near, the convergence excess decreased only in some of the patients while wearing bifocals. Conventional strabismus surgery to reduce the basic angle has a positive influence. A Fadenoperation is only necessary in a few cases.

Effect of collection and preprocessing methods on neutrophil elastase plasma concentrations

OBJECTIVES

Elevated plasma levels of the elastase alpha 1-proteinase inhibitor complex (E-alpha 1 PI) have been proposed as a marker of bacterial infection and neutrophil activation. Liberation of elastase from neutrophils after collection of blood may cause falsely elevated results. Collection methods have not been validated for critically ill neonates and children. We evaluated the influence of preanalytical methods on E-alpha 1 PI results including the recommended collection into EDTA tubes.

DESIGN AND METHODS

First, we compared varying acceleration speeds and centrifugation times. Centrifugation at 1550 g for 3 min resulted in reliable preparation of leukocyte free plasma. Second, we evaluated all collection tubes under consideration for absorption of E-alpha 1 PI. Finally, 12 sets of samples from healthy adults and 42 sets obtained from critically ill neonates and children were distributed into the various sampling tubes. Samples were centrifuged within 15 min of collection and analyzed with a new turbidimetric assay adapted to routine laboratory analyzers.

RESULTS

One of the two tubes containing a plasma-cell separation gel absorbed 22.1% of the E-alpha 1 PI content. In the remaining tubes without absorption of E-alpha 1 PI no differences were observed for samples from healthy adult patients. However, in samples from critically ill neonates or children, significantly higher results were obtained for plain Li-heparin tubes (mean = 183 micrograms/L), EDTA tubes (mean = 93 micrograms/L), and citrate tubes (mean = 88.5 micrograms/L) than for the Li-hep tube with cell-plasma separation gel and no absorption of E-alpha 1 PI (mean = 62.4 micrograms/L, p < 0.01).

CONCLUSION

Contrary to healthy adults, E-alpha 1 PI results in plasma samples from critically ill neonates and children depend on the type of collection tube.

Somatic hypermutation in normal and transformed human B cells

In the human, most IgM+IgD+ as well as CD5+ peripheral blood B cells express unmutated V genes and thus can be assigned to a pre-germinal centre (GC) stage of development. The memory B-cell compartment generated in the GC reaction and characterized by cells bearing somatically mutated V-region genes consists not only of class-switched cells, but also of IgM-only B cells and perhaps a subset of IgM+IgD+B cells expressing the CD27 antigen. Comparison of the rearranged V-region genes of human B-cell lymphomas with those of the normal B-cell subsets allows the identification of the progenitor cells of these tumours in terms of their stage of maturation. On this basis, most B-cell non-Hodgkin lymphomas, and in addition Hodgkin and Reed-Sternberg (HRS) cells in Hodgkin's disease (HD), are derived from B cells at a GC or post-GC stage of development. The mutation pattern indicates that the precursors of the tumour clones have been stringently selected for expression of a functional antigen receptor with one notable exception: HRS cells in classical (but not lymphocyte-predominant) HD appear to be derived from "crippled" GC B cells. Sequence analysis of rearranged V genes amplified from single tonsillar GC B cells revealed that the somatic hypermutation process introduces deletions and/or insertions into V-region genes more frequently than indicated by previous investigations. Presumably, this feature of the hypermutation mechanism is often responsible for the generation of heavy chain disease, and also several types of chromosomal translocations of oncogenes into immunoglobulin loci in human B-cell lymphomas.

Exposure to carbon black: a cancer risk?

Lung cancer is one of the most serious health problems in the industrial nations and is therefore of great public and scientific interest. Although inhalative cigarette smoking is without doubt the main cause for the increasing frequency of lung cancer, during recent years there has been more and more public interest in other substances in the environment or at the work place that are assumed to be potentially carcinogenic especially due to experiences with fibrous particles such as asbestos and their effects. Enhanced attention is also directed to inert or nuisance dusts such as carbon black. Evaluation of the possibly increased risk for humans should first be based on exact epidemiology data. In the absence of those data--as in the case of carbon black--experimental data in animals serve as the point of orientation, especially results gained in rats in long-term inhalation studies. Pathologic anatomy investigations of human lungs under similar exposure conditions, however, render results quite different from those obtained in rats and, thus, preclude ready interpretation of animal results to human risk assessment. This is particularly true for the development of lung tumors in rats under overload conditions as well as for certain tumor types not observed in human lung tissues. It is therefore quite understandable that many researchers propose to interpret the changes observed in rat lung tissues after inhalation of carbon black as rat-specific reaction mechanisms that cannot be applied to human tissues, which in the past have led to the wrong conclusions regarding human risk assessment due, among other factors, to incorrect experimental design and inaccurate nomenclature of tumorous lesions in rats.

[Comparison of HLA typing and retyping data in patients with bone marrow transplantation]

Comparing HLA data from 851 patients with serological HLA-A, -B, -DR and/or PCR-SSO HLA-DRB, -DQB reevaluated HLA types produced 107 (12.5%) different results. The high discrepancy of HLA data from patients confirm the demand for a serological HLA-A, -B and a DNA HLA-DRB, -DQB reevaluation before starting an unrelated donor search for bone marrow transplantation. The reliability of serological HLA-DRB, -DQB typing was evaluated as 97.8%, whereas DNA HLA-DRB, -DQB typing was 99.5%.

[Burns from undisclosed acids in a liquid used by temporary workers. A recent problem in occupational medicine caused by a lack of information]

HISTORY

Two temporary labourers, on piece work without sufficient prior instructions, were employed to clean a house facade. During the work, at first limited to 5-10 minutes, they sustained chemical burns from the hydrofluoric and hydrochloric acids contained in the liquid used to clean the stone. Both workers had been left uniformed about the danger or kind of the material being used, because of their short-time employment. They only sought medical help several hours later.

ADMISSION FINDINGS

At the areas of contact with the cleansing liquid (hands, lower arms and thighs, in case 1; additionally at first well circumscribed and very painful areas of erythema, developing within a few hours into blisters, in case 2; also erosions in both).

INVESTIGATIONS

Chemical burns by hydrofluoric acid were only elucidated as the cause 24 hours after exposure. Repeat tests (ECG, blood gas analysis, electrolyte levels) provided no evidence of deep-seated burns at the contact areas or systemic poisoning. Radiology of the hand was normal.

TREATMENT AND COURSE

As there was at first no indicative history, toxic contact dermatitis was suspected and treated topically with Clobetasol-17-propionate. Once the true cause became known treatment consisted of compresses with 10% calcium gluconate solution. All lesions healed completely within 4 and 6 days, respectively.

INTERPRETATION

Temporary workers are often insufficiently instructed, despite clear legal regulations. Such lack of informations increases the risk of harm to workers and makes appropriate treatment more difficult.

Evidence for local 32 symmetry in homotrimeric riboflavin synthase of Escherichia coli

Riboflavin synthase is a trimer of identical 23-kDa subunits. The primary structure is characterized by considerable similarity of the C-terminal and N-terminal parts. Recombinant riboflavin synthase of Escherichia coli and Bacillus subtilis was crystallized by the vapor diffusion method. Crystals of E. coli riboflavin synthase belong to the orthorhombic system, space group P2(1)2(1)2(1), with unit cell dimensions a = 53.2 A, b = 117.6 A, c = 150.9 A, alpha = beta = gamma = 90 degrees. They diffract to better than 3.3 A resolution and have presumably one trimer in the asymmetric unit. The self rotation function indicates local 32 symmetry. Twofold local symmetry is an unexpected result in a trimeric protein. In conjunction with primary structure arguments and mechanistic considerations, we propose that the protein is a pseudohexamer where each of the peptide subunits fold into two topologically similar domains.

Differentiation of phylogenetically related slowly growing mycobacteria based on 16S-23S rRNA gene internal transcribed spacer sequences

Interspecific polymorphisms of the 16S rRNA gene (rDNA) are widely used for species identification of mycobacteria. 16S rDNA sequences, however, do not vary greatly within a species, and they are either indistinguishable in some species, for example, in Mycobacterium kansasii and M. gastri, or highly similar, for example, in M. malmoense and M. szulgai. We determined 16S-23S rDNA internal transcribed spacer (ITS) sequences of 60 strains in the genus Mycobacterium representing 13 species (M. avium, M. conspicuum, M. gastri, M. genavense, M. kansasii, M. malmoense, M. marinum, M. shimoidei, M. simiae, M. szulgai, M. triplex, M. ulcerans, and M. xenopi). An alignment of these sequences together with additional sequences available in the EMBL database (for M. intracellulare, M. phlei, M. smegmatis, and M. tuberculosis) was established according to primary- and secondary-structure similarities. Comparative sequence analysis applying different treeing methods grouped the strains into species-specific clusters with low sequence divergence between strains belonging to the same species (0 to 2%). The ITS-based tree topology only partially correlated to that based on 16S rDNA, but the main branching orders were preserved, notably, the division of fast-growing from slowly growing mycobacteria, separate branching for M. simiae, M. genavense, and M. triplex, and distinct branches for M. xenopi and M. shimoidei. Comparisons of M. gastri with M. kansasii and M. malmoense with M. szulgai revealed ITS sequence similarities of 93 and 88%, respectively. M. marinum and M. ulcerans possessed identical ITS sequences. Our results show that ITS sequencing represents a supplement to 16S rRNA gene sequences for the differentiation of closely related species. Slowly growing mycobacteria show a high sequence variation in the ITS; this variation has the potential to be used for the development of probes as a rapid approach to mycobacterial identification.

Functional MR of frontal lobe activation: comparison with Wada language results

PURPOSE

Our purpose was to determine the utility of functional MR imaging in conjunction with a word-generation paradigm in the assessment of language lateralization.

METHODS

Functional MR imaging and Wada testing for language lateralization was performed in patients with complex partial seizures during the performance of word-generation tasks. A language lateralization quotient was calculated from the number of activated pixels in the right and left hemispheres. A language laterality score was derived from the Wada results as the percentage of correct responses during right internal carotid artery injection minus the percentage of correct responses during left internal carotid injection. A correlation coefficient between the functional MR imaging results and the Wada language laterality scores was calculated.

RESULTS

In 13 patients, hemispheric dominance based on Wada testing was confirmed by functional MR imaging during silent word generation. The Wada laterality scores varied from 100 to -100 and the functional MR imaging scores varied from 100 to -10. The language lateralization scores determined by functional MR imaging correlated significantly with the language lateralization scores derived from Wada testing.

CONCLUSION

Functional MR imaging performed during word generation is an accurate method for lateralizing language function in patients with complex partial epilepsy.

The 1.25 A crystal structure of sepiapterin reductase reveals its binding mode to pterins and brain neurotransmitters

Sepiapterin reductase catalyses the last steps in the biosynthesis of tetrahydrobiopterin, the essential co-factor of aromatic amino acid hydroxylases and nitric oxide synthases. We have determined the crystal structure of mouse sepiapterin reductase by multiple isomorphous replacement at a resolution of 1.25 A in its ternary complex with oxaloacetate and NADP. The homodimeric structure reveals a single-domain alpha/beta-fold with a central four-helix bundle connecting two seven-stranded parallel beta-sheets, each sandwiched between two arrays of three helices. Ternary complexes with the substrate sepiapterin or the product tetrahydrobiopterin were studied. Each subunit contains a specific aspartate anchor (Asp258) for pterin-substrates, which positions the substrate side chain C1'-carbonyl group near Tyr171 OH and NADP C4'N. The catalytic mechanism of SR appears to consist of a NADPH-dependent proton transfer from Tyr171 to the substrate C1' and C2' carbonyl functions accompanied by stereospecific side chain isomerization. Complex structures with the inhibitor N-acetyl serotonin show the indoleamine bound such that both reductase and isomerase activity for pterins is inhibited, but reaction with a variety of carbonyl compounds is possible. The complex structure with N-acetyl serotonin suggests the possibility for a highly specific feedback regulatory mechanism between the formation of indoleamines and pteridines in vivo.

Isoform specificity in the relationship of actin to dendritic spines

Dendritic spines contain high concentrations of actin, but neither the isoforms involved nor the mechanism of accumulation is known. In situ hybridization with specific probes established that beta- and gamma-cytoplasmic actins are selectively expressed at high levels by spine-bearing neurons. Transfecting cultured hippocampal neurons with epitope-tagged actin isoforms showed that cytoplasmic beta- and gamma-cytoplasmic actins are correctly targeted to spines, whereas alpha-cardiac muscle actin, which is normally absent from neurons, formed aggregates in dendrites. The transfected actin cDNAs contained only coding domains, suggesting that spine targeting involves amino acid sequences in the proteins, an interpretation supported by experiments with chimeric cDNAs in which C-terminal actin sequences were found to be determinative in spine targeting. By contrast to actin, microtubule components, including tubulin and MAP2, were restricted to the dendritic shaft domain. The close association of cytoplasmic actins with spines together with their general involvement in cell surface motility further supports the idea that actin motility-based changes in spine shape may contribute to synaptic plasticity.

Anti-carcinoembryonic antigen antibodies versus somatostatin analogs in the detection of metastatic medullary thyroid carcinoma: are carcinoembryonic antigen and somatostatin receptor expression prognostic factors?

BACKGROUND

Surgery is currently the only potentially curative approach in the treatment of medullary thyroid carcinoma (MTC). In many instances however, postsurgically elevated or rising plasma calcitonin and/or carcinoembryonic antigen (CEA) levels indicate persistent metastatic disease, although conventional diagnostic procedures (computed tomography (CT), magnetic resonance imaging (MRI), and invasive venous catheterization) fail to localize the responsible lesions. Recently, anti-CEA antibodies and somatostatin analogs have shown promising results in the staging of MTC. The aim of this study was to compare the sensitivity of both methodologies, especially for the detection of occult MTC, and to assess whether there may be correlations between the scintigraphic behavior and the patients' prognosis.

METHODS

A total of 26 patients with medullary thyroid carcinoma were examined at our institution between 1977 and 1996. Ten of them had known disease, 14 had occult metastatic MTC, and 2 were free of disease at the time of presentation. Fourteen patients were investigated with anti-CEA monoclonal antibodies (MAbs) (receiving a total of 35 injections: clones BW431/26, BW431/31, IMACIS, or F023C5, labeled with 99mTc, (111)In or (131)I), and 8 patients were studied with (111)In-labeled octreotide. Two patients received potentially therapeutic doses of (131)I-labeled anti-CEA antibodies. All patients underwent conventional radiologic evaluation (ultrasonography, CT, and MRI) and/or biopsy within 4 weeks. Additional imaging was performed with 99mTc-(V)-DMSA, (131)I-metaiodobenzylguanidine, 201thallium chloride, 99mTc-methylene diphosphate, and/or 18F-fluorodeoxyglucose-positron emission tomography. Clinical follow-up was obtained.

RESULTS

All patients with established disease had elevated plasma CEA (range, 6.8-345 ng/mL; calcitonin levels between 92 and 11,497 pg/mL), whereas in 9 of 14 occult cases, levels were < or = 5 ng/mL (range, 0.6-829 ng/mL; calcitonin, 72-2920 pg/mL). In patients with known disease, the overall lesion-based sensitivity was 86% for the anti-CEA MAbs, whereas octreotide was unable to target any tumor in patients with rapidly progressing disease or distant metastases (overall sensitivity, 47%). In all patients with occult MTC, anti-CEA MAbs and octreotide were able to localize at least one lesion (patient-based sensitivity, virtually 100%). In patients with postsurgically persistent hypercalcitoninemia, cervical lymph nodes were identified as the most frequent site of metastases, whereas in patients with occult and slowly progressing disease several years after primary surgery, anti-CEA MAbs and octreotide showed bilateral involvement of mediastinal lymph nodes; however, tumor to nontumor ratios were usually higher with octreotide in these cases. With anti-CEA Mabs, the highest tumor to nontumor ratios were observed in clinically aggressive, rapidly progressing disease. The sensitivity of all other diagnostic modalities was, at < or = 50%, significantly lower. Indication for antitumor effects was observed in a patient receiving 65 mCi of (111)I-labeled F(ab')2 fragments of the clone F023C5.

CONCLUSIONS

For the detection of occult MTC, anti-CEA MAbs and octreotide seem to have a sensitivity that is superior to conventional diagnostic modalities, especially also when used in combination. Better detectability with anti-CEA antibodies (which may result in higher CEA expression) seems to be associated with more aggressively growing forms of MTC, whereas somatostatin receptor expression at normal CEA plasma levels and weaker MAb targeting may be associated with a more benign clinical course. This is in accordance with the study of Busnardo et al. (Cancer 1984; 53:278-85), who showed higher CEA serum levels to be associated with a worse prognosis, as well as with the in vitro findings of Reubi et al. (Lab Invest 1991;64:567-73), who demonstrated lower somatostatin receptor expression in less differentiated MTC. Fu

The Saccharomyces cerevisiae CCH1 gene is involved in calcium influx and mating

The yeast Saccharomyces cerevisiae gene CCH1 (ORF YGR217w) shows high homology with animal calcium channel alpha1-subunit genes. Knock-out mutants were constructed of Cch1 and of Mid1 which is known to mediate Ca2+ influx in response to the alpha-mating pheromone. Cch1 is involved in calcium influx and the late stage of the mating process. The cch1 mutant sensitivity against the alpha-mating pheromone can be reduced by the addition of extra calcium. The product of this gene is likely to interact with the MID1 gene product in Ca influx or its control.

Interleukin-6 receptor-interleukin-6 fusion proteins with enhanced interleukin-6 type pleiotropic activities

An sIL-6R/IL-6 chimera, directly fusing the natural forms of soluble IL-6 receptor and IL-6, as found in human body fluids, was produced in transfected human cells. The secreted p85 glycoprotein was active at a concentration of 120 pM to produce growth-arrest and spindleoid differentiation of murine melanoma F10.9 cells, which do not respond to IL-6 alone. This fusion protein was as active as the yeast-produced p56 fusion protein containing a shortened sIL-6R, linked through a flexible peptide chain to IL-6 (Hyper IL-6). The concentration of Hyper IL-6 needed to arrest the growth of F10.9 cells was much lower than that needed of a combination of IL-6 and sIL-6R, added separately. Hyper IL-6 was also more active than IL-6 in stimulating growth of murine plasmacytoma T1165 cells, the half maximal stimulation being obtained at 2 pM Hyper IL-6 versus 23 pM for IL-6. In order to evaluate the effect of the fused sIL-6R/IL-6 proteins on human hematopoietic primitive progenitor cells, they were added to suspension cultures of CD34+ cells from human cord blood in addition to both flt3/flk2 ligand (FL) and stem cell factor (SCF). Fused sIL-6R/IL-6 produced a marked stimulation of cell expansion and a marked increase in the number of colony forming units when subsequently plated in semi-solid medium with IL-3, GM-CSF, SCF and erythropoietin. Ex-vivo maintenance and expansion of early progenitor cells in bone marrow transplantation protocols may be a potential application for the sIL-6R/IL-6 chimeric glycoproteins.

Mating structure and inbreeding and outbreeding depression in the rare plant Gentianella germanica (Gentianaceae)

Isolation and small size of populations as a result of habitat destruction and fragmentation may negatively affect plant fitness through pollinator limitation and increased levels of inbreeding. To increase genetic variation in small populations of rare plants artificial gene flow has been suggested as a management tool. We investigated whether pollinator limitation and inbreeding depression could reduce fitness in Gentianella germanica, an endangered biennial of increasingly fragmented calcareous grasslands in Central Europe. We experimentally excluded pollinators and generated progenies by hand-pollinating flowers with pollen from different distances. G. germanica was highly selfing. Pollinator exclusion strongly reduced seed set, indicating that pollinator limitation could potentially reduce plant fitness. Germination rate as well as number of leaves and rosette size of progeny from 10-m crosses was higher than that of progeny from open pollinations, self-, 1-m, and interpopulation crosses. After 6 mo of growth differences in the number of surviving plants persisted, whereas differences in plant size did not. The results suggest that inbreeding depression may reduce plant performance in G. germanica. Outbreeding depression in the performance of progeny from interpopulation crosses indicates that caution is necessary in using artificial interpopulation gene flow as a management tool.

Functional role of beta2-adrenoceptors in the transplanted human heart

In the transplanted human heart, beta-adrenoceptor subtypes change with time after transplantation: beta1-adrenoceptors tend to decline, whereas beta2-adrenoceptors are upregulated. The aim of this study was to determine whether, in the transplanted human heart, stimulation of beta2-adrenoceptors can induce heart-rate increases. For this purpose, we assessed in eight heart-transplant recipients (mean posttransplant time: 932 days) the effects of infusion of graded doses of isoprenaline (3.5-35 ng/kg/min) 120 min after pretreatment with the beta1-adrenoceptor antagonist bisoprolol (10 mg p.o.; beta1-adrenoceptor occupancy approximately 80%; beta2-adrenoceptor occupancy <5%) on heart rate in the recipient's native (innervated) and transplanted (denervated) sinus nodes. Isoprenaline, acting under these conditions predominantly at beta2-adrenoceptors, increased heart rate both in the recipient's transplanted and native sinus nodes in a dose-dependent manner; at each dose, increases were significantly higher in the transplanted than in the native sinus node. ED20 values (dose to increase heart rate by 20 beats/min) in the transplanted sinus node were 22.2 +/- 1.8 ng/kg/min, and in the native, >35 ng/kg/min (p < 0.01). We conclude that in the transplanted human heart, beta2-adrenoceptor stimulation does evoke increases in heart rate. The enhanced response to isoprenaline in the transplanted sinus node could be caused by the upregulated beta2-adrenoceptors or by the fact that during isoprenaline infusion, vagal activity increases, thus blunting the response in the native (innervated) but not in the transplanted (denervated) sinus node.

A hitherto unknown splice site defect in the protein S gene (PROS1): the mutation results in allelic exclusion and causes type I and type III protein S deficiency

A hitherto unknown splice site mutation, in the splice acceptor of intron B (tctag to tctgg), was identified in a symptomatic patient with type III protein S deficiency. The mutation co-segregated with type I/III protein S deficiency in the patient's family. RNA analysis showed allelic exclusion of the mutant transcript in affected individuals. The apparent type III deficiency in the propositus was not associated with the protein S Heerlen variant.

The active sites of the eukaryotic 20 S proteasome and their involvement in subunit precursor processing

The 26 S proteasome is the central protease involved in ubiquitin-mediated protein degradation and fulfills vital regulatory functions in eukaryotes. The proteolytic core of the complex is the 20 S proteasome, a cylindrical particle with two outer rings each made of 7 different alpha-type subunits and two inner rings made of 7 different beta-type subunits. In the archaebacterial 20 S proteasome ancestor proteolytically active sites reside in the 14 uniform beta-subunits. Their N-terminal threonine residues, released by precursor processing, perform the nucleophilic attack for peptide bond hydrolysis. By directed mutational analysis of 20 S proteasomal beta-type proteins of Saccharomyces cerevisiae, we identified three active site-carrying subunits responsible for different peptidolytic activities as follows: Pre3 for post-glutamyl hydrolyzing, Pup1 for trypsin-like, and Pre2 for chymotrypsin-like activity. Double mutants harboring only trypsin-like or chymotrypsin-like activity were viable. Mutation of two potentially active site threonine residues in the Pre4 subunit excluded its catalytic involvement in any of the three peptidase activities. The generation of different, incompletely processed forms of the Pre4 precursor in active site mutants suggested that maturation of non-active proteasomal beta-type subunits is exerted by active subunits and occurs in the fully assembled particle. This trans-acting proteolytic activity might also account for processing intermediates of the active site mutated Pre2 subunit, which was unable to undergo autocatalytic maturation.