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Biomedical subjects

U Weiss

Publications and source records attributed to U Weiss.

At least 19 recordsLinked to original sources
PubMed1992

Accumulation of somatic mutants in the B cell compartment after primary immunization with a T cell-dependent antigen.

The accumulation of somatic mutants in splenic B lymphocytes early after primary immunization with the hapten (4-hydroxy-3-nitro-phenyl)acetyl (NP) coupled to chicken gamma globulin (CG) was determined. Rearranged V186.2 heavy chain genes were amplified by the polymerase chain reaction from genomic DNA and subjected to nucleotide sequence analysis. Somatic antibody mutants become detectable on day 6 after immunization, and most of the somatic mutations accumulating in the memory compartment are introduced until day 14. At this time strong selection for mutants expressing high binding affinity for NP is apparent. Extrapolation from the mutation frequency increases between day 6 and day 14 to the previously determined mutation frequency at week 6 (Weiss. U. and Rajewsky, K., J. Exp. Med. 1990, 172: 1681) leads to the prediction that the process of mutant generation ceases to operate around day 22 after primary immunization.

Amino Acid Sequence↗
PubMed1992

Widespread occurrence of chromogranins/secretogranins in the matrix of secretory granules of endocrinologically silent pituitary adenomas.

To investigate the constituents of the matrix of endocrine secretory granules, we analyzed endocrinoilogically silent ("non-functioning") human pituitary adenomas for the occurrence of the chromogranins/secretogranins (granins), a protein family normally stored together with many different hormones. When five non-functioning pituitary adenomas were analyzed by immunoblotting using polyclonal and monoclonal antibodies specific for individual members of the granin family, chromogranin A was detected in four cases and chromogranin B and secretogranin II were detected in all cases. The cellular distribution of the granins and of various hormones known to be expressed in the anterior pituitary was studied by immunocytochemistry in fixed, frozen tissue sections from five additional adenomas. Of the eight hormones investigated, only thyroid-stimulating hormone, luteinizing hormone, and follicle-stimulating hormone were detected, occurring in only two of the five adenomas. In contrast, granins were found in all five tumors. Chromogranin B and secretogranin II were detected in each of the adenomas in virtually every cell studied, whereas chromogranin A exhibited such a widespread cell distribution in only three adenomas, being focally present in one and absent from the other tumor. The subcellular localization of the granins and the three glycoprotein hormones was investigated by double immunoelectron microscopy. Chromogranin A and chromogranin B were mainly co-localized in secretory granules, whereas secretogranin II was either co-localized with the other two granins or segregated to different secretory granules. When present, glycoprotein hormones were immunodetected in both the secretory granules containing all three granins and those containing mainly secretogranin II. Our data indicate that in non-functioning pituitary adenomas chromogranin A is differentially expressed from chromogranin B and secretogranin II. Moreover, the granins appear to be the most widespread constituents of endocrine secretory granules known, forming the dense-core matrix irrespective of the presence or absence of hormones.

Adenoma↗
PubMed1991

Intraclonal generation of antibody mutants in germinal centres.

The generation and selection of somatic antibody mutants are key elements of acquired immunity, essential for the affinity maturation of antibody responses dependent on T cells. The mutants are generated through a mechanism that introduces point mutations at high rate into rearranged variable (V) region genes in the course of cell proliferation. Their appearance coincides with the generation of germinal centres, which are characterized by oligoclonal B-cell proliferation and have been suggested to be the microenvironment in which antibody mutants are generated. We report here direct evidence for this hypothesis. Rearranged V-region genes were amplified from the genomic DNA of cells picked from individual germinal centres. The sequence analysis of these genes revealed that most represent cells of distinct B-cell clones which expanded locally, generating somatic antibody mutants at high rate. By contrast, antigen-induced proliferation of B cells at another site, periarteriolar lymphocyte sheath-associated foci, was not associated with somatic hypermutation.

Amino Acid Sequence↗
PubMed1990

The repertoire of somatic antibody mutants accumulating in the memory compartment after primary immunization is restricted through affinity maturation and mirrors that expressed in the secondary response.

The anti-(4-hydroxy-3-nitro-phenyl)acetyl (NP) response is dominated by lambda 1 chain-bearing antibodies expressing the VH gene V186.2 in combination with the D element DFL16.1. lambda 1-positive B cells were isolated from the spleens of mice immunized with NP-chicken gamma globulin 6 wk earlier. Rearranged V186.2 genes were amplified from the genomic DNA of these cells and sequenced. In cases where the rearrangement was typical for secondary anti-NP antibodies, the VHDJH sequences were generally heavily mutated. The frequency and the nature of the nucleotide exchanges mirrored those of secondary response antibodies. V186.2 genes with other rearrangements and V186.2-related genes isolated concomitantly were essentially unmutated. These results demonstrate: (a) that somatic antibody mutants are largely restricted to a small compartment of peripheral B cells, namely, that of memory cells; (b) that the memory compartment is strongly selected for high affinity precursors and largely purged from antigen-binding loss mutants; and (c) that the repertoire of binding specificities expressed in the secondary response is established in its final form before secondary immunization.

Amino Acid Sequence↗
PubMed1990

Requirement for GTP hydrolysis in the formation of secretory vesicles.

The specificity of vesicular transport in a cell is determined by the formation of vesicles with specific contents from a donor compartment and their selective fusion with the appropriate acceptor compartment. Several of the latter fusion steps have been investigated in detail using cell-free systems, and work with these systems as well as genetic evidence has revealed a role for GTP-binding proteins in membrane fusion processes. We have reconstituted the formation of constitutive secretory vesicles and immature secretory granules from the trans Golgi network in a cell-free system. We show here that the budding of both types of post-Golgi vesicles is inhibited by non-hydrolysable analogues of GTP, which suggests a more widespread role for GTP-binding proteins in membrane traffic than previously assumed.

Animals↗
PubMed1989

Structure of elsinochrome A: a perylenequinone metabolite.

trans-1,2-Diacetyl-1,2-dihydro-5,10-dihydroxy-3,7,8,12- tetramethoxybenzo[ghi]perylene-4,11-dione, C30H24O10, Mr = 544.51, orthorhombic, P2(1)2(1)2(1), Z = 4, a = 12.428 (3), b = 13.048 (3), c = 14.933 (3) A, V = 2421.5 (9) A3, Dx = 1.494, Dm (by flotation) = 1.48 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 1.057 cm-1, F(000) = 1136, T = 293 K, R = 0.046 (2065 observed reflections). Elsinochrome A is shown to exist in the solid state as a nonplanar quinone tautomer; the pigment adopts a helical conformation, in analogy with the related cercosporin, but the perylenequinone moiety in elsinochrome A appears to be significantly less skewed.

Benz(a)Anthracenes↗
PubMed1989

Effects of nicks on repair of single-stranded loops in heteroduplex DNA in mammalian cells.

Heteroduplexes that contain single-stranded loops are repaired very efficiently in mammalian cells. The strand that does not contain the loop is used as the template strand for repair nearly twice as often as the looped strand. In this study we tested the influence of nearby nicks on the choice of template strand. We find that strand selection in repair of heteroduplexes with single-stranded loops is influenced by the presence of a nick located 71 or 125 base pairs from the loop, but only to a minor degree. Thus the loop itself is a stronger signal for repair than is a nearby nick. On the other hand, if a break is introduced into the single strand that forms the loop, the looped strand is marked for excision and rarely, if ever, is used as the template for repair.

Animals↗
PubMed1989

An antibody against secretogranin I (chromogranin B) is packaged into secretory granules.

We have investigated the sorting and packaging of secretory proteins into secretory granules by an immunological approach. An mAb against secretogranin I (chromogranin B), a secretory protein costored with various peptide hormones and neuropeptides in secretory granules of many endocrine cells and neurons, was expressed by microinjection of its mRNA into the secretogranin I-producing cell line PC12. An mAb against the G protein of vesicular stomatitis virus--i.e., against an antigen not present in PC12 cells--was expressed as a control. The intracellular localization and the secretion of the antibodies was studied by double-labeling immunofluorescence using the conventional and the confocal microscope, as well as by pulse-chase experiments. The secretogranin I antibody, like the control antibody, was transported along the secretory pathway to the Golgi complex. However, in contrast to the control antibody, which was secreted via the constitutive pathway, the secretogranin I antibody formed an immunocomplex with secretogranin I, was packaged into secretory granules, and was released by regulated exocytosis. Our results show that a constitutive secretory protein, unaltered by genetic engineering, can be diverted to the regulated pathway of secretion by its protein-protein interaction with a regulated secretory protein. The data also provide the basis for immunologically studying the role of luminally exposed protein domains in the biogenesis and function of regulated secretory vesicles.

Ammonium Chloride↗
PubMed1988

Heteroduplex-induced mutagenesis in mammalian cells.

We have shown previously that heteroduplexes containing single-stranded loops are repaired efficiently in monkey cells, but not always correctly: 2% of the repair products acquired mutations within a 350 base-pair target (Weiss, U. and Wilson, J.H., Proc. Natl. Acad. Sci. USA 87:1123-1126, 1987). The structures of the mutant genomes, which are described here, are consistent with an error-prone repair system. The spectrum of mutations includes about 25% point mutations and 75% rearrangements, which consist of deletions, duplications, and substitutions. The mutations are clustered in the vicinity of single-stranded loops in the original heteroduplex. The high frequency of mutation, their clustering, and the positions of rearrangement endpoints suggest that the mutations were generated during repair of the heteroduplexes.

Animals↗
PubMed1987

Repair of single-stranded loops in heteroduplex DNA transfected into mammalian cells.

Repair of heteroduplex DNA, generated between two interacting DNA molecules during homologous recombination, has been implicated as a contributing factor in the process of gene conversion. To assess patterns of heteroduplex repair in mammalian cells, we constructed 13 different heteroduplexes from simian virus 40 wild-type and deletion mutant DNAs. Each heteroduplex contained one or multiple single-stranded loops in the intron of the gene for large tumor antigen, which is not essential during lytic infection. After transfection into cultured monkey cells, cellular repair was evaluated by restriction analysis of the amplified viral progeny from 1123 individual plaques, each representing the clonal expansion of a single repair event. Single-stranded loops were corrected prior to replication with an overall efficiency of 90%. At the position of a loop, one of the two heteroduplex strands served as a template for accurate repair 98% of the time. Repair of single-stranded loops was biased nearly 2 to 1 in favor of the strand without the loop. The efficiency, accuracy, and strand bias of repair were unaffected by loop size within the tested range, which was 25-247 nucleotides. The excision tract associated with repair of single-stranded loops rarely exceeds 200-400 nucleotides in length.

Cell Line↗
PubMed1983

Effects of diltiazem on vulnerability to atrial and ventricular reentrant arrhythmias in the normal and ischemic heart.

In experiments on 20 artificially ventilated anaesthetized dogs, the effects of the new calcium antagonist diltiazem on the stimulation thresholds to repetitive extrasystoles and fibrillation of the atria and the ventricles, respectively, and on ventricular dysrhythmias 6-24 h after acute coronary occlusion were investigated. The electrophysiological studies were performed using different methods of programmed stimulation of the heart. The results show that therapeutic doses of diltiazem provide no protection against stimulus-induced supraventricular reentrant arrhythmias with the AV-node not involved in the reentrant circus, and have no antifibrillatory efficacy in electrically induced ventricular arrhythmias in the non-ischemic heart. In acute myocardial infarction there is no antiarrhythmic effect either. Our results can be explained by the fact that diltiazem is a specific calcium antagonist and that the slow response plays only a minor role in the arrhythmias investigated.

Animals↗
PubMed1981

Preparation and physiological properties of alkyl esters of 2,3-dihydroxypropionic acid.

In order to investigate the physiological behavior of alkyl esters of 2,3-dihydroxypropionic acid two such compounds have been synthesized. One of them, the 1-dodecylester of 2,3-ditetradecyloxypropionic acid was subjected to digestion by pancreatic lipase. The substance remained unaffected. For an in vivo experiment a doubly labelled homolog, the [1'-14C]decyl ester of 2,3-di[1'-3H]hexadecyloxypropionic acid was synthesized. This compound was fed by stomach tube to three groups of male albino rats. The experimental animals were killed after 2,4 and 6 h, those of the control groups after 6 h. Blood, urine, small intestines and livers were examined for radioactivity. From the recovery rates it could be derived that the molecule had been metabolized and absorbed. Obviously, the alkyl chain labelled with 14C was split off first and the alkyl chains labelled with 3H were split off thereafter. As the substance is metabolized in vivo it cannot be utilized as a 'non-fattening fat'.

Animals↗