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At least 433 records · Page 24Linked to original sources
PubMed1981

The maximum density of anopheline mosquitoes that can be permitted in the absence of continuing transmission of filariasis.

Using two years of mosquito collections from two fixed stations on Guadalcanal it was possible to compare the average man-biting rate with the prevalence of microfilaraemia. One area was found to be free of infection while the other still had one positive case. The DDT residual spraying had caused a change in biting habits of A. farauti No. 1 allowing a greater density of mosquitoes to bite man at times when they had lower microfilaria densities. This difference was compared with the pre-spray density so that the maximum permissible number of mosquitoes biting man without transmission of filariasis taking place, could be calculated. A theoretical value for m of 19.84 had been worked out previously; this study gave a corrected observed value of m of approximately 20, very close to the calculated theoretical value. The situation studied here probably showed incomplete interruption of transmission, so it was considered preferrable to recommend a figure of 0.66 average vector man-biting rate per hour indoors for the critical value.

Animals↗
PubMed1990

Expression of plasmid-encoded structural proteins permits engineering of bacteriophage T4 assembly.

A complementation system for studying bacteriophage T4 tail assembly has been developed and used to test the effects of nonviable mutations on the function of a specific T4 tail protein, gp48. The complementation system assays the assembly function of gp48 without requiring that viable phage be produced, circumventing the operational problems of maintaining nonviable mutants of this lytic bacteriophage. The protein to be tested was preexpressed from cloned genes in a host cell prior to infection with the challenge phage. Assembly activity was assayed by monitoring the conversion of one tail assembly intermediate, the baseplate lacking gp48, into baseplates containing gp48 or into tube baseplates (or sheathed tails) assembled from such baseplates. Specific incorporation of gp48 into these structures was confirmed using gp48-specific antiserum, and the same serum was used in direct immunoelectron microscopy experiments to localize gp48 to the baseplate-proximal end of the T4 tail tube, at the site where the tube and sheath bind to the baseplate. The protein gp48 has been previously shown to be a baseplate protein, as well as a tail-tube-associated protein, and was tested for a possible role as a tail-length tape-measure protein. Tests with a deleted variant of gp48 were inconclusive because the protein was inactive. A variant of gp48, 20% longer than wild-type protein due to an internal duplication, was found to be partly functional in our assembly complementation system. This abnormally elongated protein allows several assembly steps to proceed, including the assembly of normal length T4 tails, implying that it does not specify tail length. The insertion-duplication variant of gp48 appears to have a defect in its interaction with the tail sheath protein, leading to abnormal sheath contraction.

Chromosome Deletion↗
PubMed1981

Mutation near the polyoma DNA replication origin permits productive infection of F9 embryonal carcinoma cells.

F9 mouse embryonal carcinoma cells are resistant to productive infection by wild-type polyoma virus. Continued passage of F9 cells initially infected with wild-type polyoma virus eventually leads to the selection of polyoma virus mutants that are capable of productive infection of undifferentiated F9 cells. Three mutants, PyF101, PyF111 and PyF441, have been plaque-purified and examined. All three PyF mutant DNAs are altered from the wild-type sequence in the Pvu II-4 fragment that spans 67.6 to 70.2 map units on the polyoma genome. PyF441 has a single base change of A to G at 69.6 map units. PyF101 and PyF111 DNAs also contain this point mutation at 69.6 map units. In addition, PyF101 and PyF111 DNAs have exact tandem duplications of 54 and 31 bp, respectively, of sequences encompassing the point mutation, and both copies of the tandem duplication have the point mutation. Other than these changes, no difference exists in the nucleotide sequences of wild-type and PyF mutant DNAs from the BcI I site at 65.6 map units clockwise through the origin of viral DNA replication to the BgI I site at 72.2 map units. DNA infections of F9 cells with wild-type-mutant hybrid DNAs formed by ligation of heterologous combinations of the small and large DNA fragments generated by double digestion with the restriction enzymes BcII and BGI I show that the DNA sequence changes described above are responsible for the ability of the PyF mutants to infect F9 cells.

Animals↗
PubMed1985

5-Azacytidine permits gene activation in a previously noninducible cell type.

We previously reported that silent muscle genes in fibroblasts could be activated following fusion with muscle cells to form heterokaryons. This activation did not require changes in chromatin structure involving significant DNA synthesis. We report here that muscle gene activation was never observed when HeLa cells were used as the nonmuscle fusion partner. However, if HeLa cells were treated with 5-azacytidine (5-aza-CR) prior to fusion, muscle gene expression was induced in the heterokaryons. The genes for both an early (5.1H11 cell surface antigen) and a late (MM-creatine kinase) muscle function were activated, but were frequently not coordinately expressed. These results suggest that the expression of two muscle genes, which is usually sequential, is not interdependent. Furthermore, changes induced by 5-aza-CR, presumably in the level of DNA methylation, are required for muscle genes in HeLa cells to be expressed in response to putative trans-acting regulatory factor(s) present in muscle cells.

Animals↗
PubMed1990

The antigen-limited nature of microtiter ELISAs requires partial depletion of IgG to permit reliable determination of rabbit serum IgA antibody activity.

The antigen-limiting nature of microtiter ELISAs predicts that antibodies of minor classes may be underestimated when the same specimen contains large amounts of IgG antibodies specific for the same antigen. Such competitive inhibition can be diagnosed from ELISA titration plots. A method is described to eliminate the negative effects of this competition on the detection of IgA antibodies in rabbit serum. The detectability of rabbit serum antibodies to ovalbumin and bovine serum albumin is increased 10-fold by prior treatment of 1:100 dilutions of serum with 1% Cowan I S. aureus. High concns of S. aureus, e.g. 10%, completely deplete serum IgG without loss of IgA. However, concns higher than 1% do not lead to additional improvement in the detectability of IgA antibodies in the systems studied. The method is rapid, inexpensive and shows no non-specific depletion of IgA from either serum or bronchoalveolar lavage fluid.

Animals↗
PubMed1995

Chimeric interleukin 2 receptor alpha chain antibody derivatives with fused mu and gamma chains permit improved recruitment of effector functions.

In order to investigate the feasibility of shuffling effector functions of monoclonal antibodies, we constructed chimeric antibodies with fused heavy chains. The derivatives studied are based on a monoclonal antibody directed against the alpha chain of the human Il2-R. Derivatives studied were the IgG1 and IgM isotypes; IgM delta, lacking the ability of multimerization due to a deletion; IgMc gamma 1 and IgGlc mu, with fused mu and gamma 1 chains and vice versa. IgG1, IgM delta and IgMc gamma 1 were secreted as monomers, IgM and IgG1c mu as polymers. The Ki values for competition with radio-iodinated Il2 with respect to binding to the Il2-R were markedly lower for polymeric than for monomeric derivatives (300-400 pM versus 2500-6500 pM). Recruitment of complement mediated by the deposition of C3 fragments, either of heterologous (rabbit) or homologous (human) origin, was mediated only by the polymeric derivatives IgM and IgG1c mu. ADCC was mediated by monomeric IgG1 and polymeric IgG1c mu, the latter derivative being active at concentrations 100-fold lower than the former. Together, the results demonstrate that both CDC and ADCC effector functions can be combined on a polymeric antibody derivative with fused gamma 1 and mu chains. In addition, such a derivative, due to its polymeric nature, has a high binding affinity. These properties may be important for the elimination of target cells in vivo.

Amino Acid Sequence↗
PubMed1982

A modification of the rapid glyoxylic acid technique permits visualization of serotonergic and hypothalamic dopaminergic neurons.

The rapidity, simplicity and reproducibility of the rapid glyoxylic acid technique (SPG) has made it the method of choice for many investigators interested in the histofluorescence of CNS catecholamine systems. Unfortunately, the serotonergic system and the dopaminergic hypothalamic cell groups are poorly visualized with this method. Using intraventricular colchicine pretreatment, reliable visualization of these systems can be obtained. The serotonergic fluorescence seen with colchicine administration is augmented by l-tryptophan pretreatment and diminished by pretreatment with para-chlorophenylalanine, a tryptophan hydroxylase inhibitor. It is relatively resistant to fading under ultra-violet illumination and photographs can be taken up to 4 weeks after the sections have been processed. Visualization of dopaminergic, hypothalamic neurons as well as visualization of the dendritic fields of all catecholaminergic neurons is comparable to that obtained with tyrosine hydroxylase immunocytohistochemistry.

Animals↗
PubMed1989

A method permitting precise trimming of resin-embedded tissue for ultrathin sectioning in pre-embedding immunoelectronmicroscopy.

Due to the high complexity of the mammalian central nervous system, sampling of immunohistochemically processed brain tissues for electronmicroscopy requires an accurate and reliable technique. For this reason, the flat-embedding method, which allows light microscopical examination of tissue before sampling, is generally employed. Because of the osmification process, however, the tissue is blackish and opaque which hampers light microscopical selection of tissue areas of interest. We have found that tissue translucency is highly improved by an osmification process using an osmium tetroxide-ferrocyanide mixture. We describe a transilluminated chuck that enables visualization of immunostaining in specimens mounted on a trimming instrument, thus allowing for extremely precise sampling of the tissue.

Animals↗
PubMed1995

A novel apparatus that permits multiple routes for infusions and body-fluid collections in a freely-moving animal.

A novel apparatus is described for simultaneous performance of multi-channel infusions/body-fluid collections and multichannel electrical recordings/stimulations in a freely behaving animals. This apparatus consists of a cylindrical cage and other devices described below. Electrical contacts are achieved via a slip-ring commutator. A rotation detector detects the turning of the animal in the cage, and a controller rotates the floor under the animal in the opposite direction by means of a stepping motor. Thus, excessive twisting of the fluid tubing between the animal and experimental equipment is released by rotation of the floor. Floor rotation starts when the animal turns in either direction and exceeds a present number of rotations. When the turning exceeds certain rates, the floor is rotated with higher angular velocities. This floor rotation little affected sleep-wake activities, brain temperature, food and water intake, and general behavior of the rat. Thus, multi-channel fluid routes have been realized; and by excluding the swivel apparatus from the fluid lines, advantages such as no fluid leakage at the swivel, no extra dead volume, and low torque to rotate the device have been gained.

Animals↗
PubMed1988

Erythrosine, a permitted food dye, is mutagenic in the Bacillus subtilis multigene sporulation assay.

Erythrosine increased the yield of sporulation minus mutants of Bacillus subtilis excision repair-proficient strain 168 by approximately equal to 400% at a concentration of 1 mg/ml under ambient light conditions. This mutagenic response was dose-dependent (0-1 mg/ml). Significantly, the food dye did not mutate the corresponding repair-deficient B. subtilis, hcr-9 (exc-). A decrease in the mutagenicity of erythrosine to B. subtilis strain 168 was apparent on metabolism by rat liver S9 mixture or by rat caecal cell-free extracts. Erythrosine did not exhibit differential toxicity to B. subtilis excision repair-proficient (168) and -deficient (hcr-9) strains, although it was highly toxic to both strains. This indicated non-involvement of excision repair in the dye-mediated toxic reactions.

Animals↗
PubMed1987

Spinal cord transplants permit the growth of serotonergic axons across the site of neonatal spinal cord transection.

These experiments were designed to determine whether transplants of fetal spinal cord tissue into lesioned spinal cord in newborn rats provide a terrain that supports the growth of serotonergic (5-HT) axons across the site of the lesion. Although descending serotonergic axons can regenerate after chemical lesions in adult animals, they show little regrowth after surgical lesions. In newborn animals, 5-HT axons do not regrow after either chemical or mechanical lesions since the axotomized raphe-spinal neurons die. After partial spinal cord lesions made in developing animals, immature axons can take an aberrant route around the site of the lesion to reach normal target areas. Even these robust, late-growing, uninjured axons, however, are unable to grow through the site of the spinal cord lesion. Immunocytochemical labeling was used to determine if descending serotonergic axons grow into fetal spinal cord transplants, and whether these axons cross the transplant to reach spinal cord levels caudal to the lesion. Spinal cord transection at a mid-thoracic spinal cord level on the day of birth resulted in a dramatic decrease in 5-HT immunoreactivity caudal to the lesion by one day postoperative. 5-HT immunoreactivity caudal to the lesion was abolished by 5 days postoperative and did not return after acute or chronic (6 months) survival periods. When a transplant of fetal spinal cord tissue was placed into the lesion site, 5-HT axons were identified throughout the transplant. At spinal cord levels caudal to the transection and transplant, the serotonergic axons were identified in the host spinal cord in both the white and gray matter. This 5-HT innervation was not confined to spinal cord segments adjacent to the lesion site but extended to spinal cord segments as far as lower lumbar levels. The reinnervation of the host spinal cord caudal to the transection was far less than that seen in unlesioned adult rat spinal cord. Horseradish peroxidase (HRP) injected caudal to the transection and transplant, retrogradely labeled neurons within the medullary raphe nuclei. The HRP and 5-HT results both depended on apposition of the transplant with the rostral and caudal stumps of the host spinal cord; without such apposition, labeling was abolished. These results indicate that the presence of a transplant at the site of the neonatal lesion modifies the environment at the lesion site in such a manner as to support the elongation of identified axons across the site of the lesion and into the host cord caudal to the lesion.

Animals↗
PubMed1993

Donor cell chimerism permitted by immunosuppressive drugs: a new view of organ transplantation.

One line of thought in organ transplantation feels that immunosuppressive drugs can lead to tolerance induction by allowing a previously unrecognized common mechanism of cell migration and microchimerism to occur, persist, and in some cases, become drug independent. It has been recognized that there is a spectrum of susceptibility of different organs to cellular rejection and that the variable ability of these organs to induce donor-specific nonreactivity reflects their comparative content of migratory leukocytes. Here, Thomas Starzl and colleagues discuss how many of the enigmas of transplantation immunology can be explained by this chimerism.

Animals↗
PubMed1987

Polyamines permit the preparation of stable Physarum core particles which have a structure similar to those from higher eukaryotes.

The inherent instability of Physarum nucleosome core particles prepared by micrococcal nuclease digestion in Na+/Ca2+ buffers can be overcome by the addition of 0.15 mM spermine and 0.5 mM spermidine. Neutron scattering, circular dichroism, nuclease digestion and thermal denaturation studies carried out on these stable monosomes show them to be very similar to those obtained from higher eukaryotes.

Animals↗
PubMed1988

Aprotinin derivatives with chromophoric leaving groups can be used as highly selective active-site titrants for serine proteinases and permit the determination of kinetic constants of enzyme-inhibitor complexes.

This paper reports a novel and valuable approach to active-site titration. The starting substance for the preparation of the active-site titrants is aprotinin (bovine pancreatic trypsin inhibitor) in which the reactive-site peptide bond, Lys15-Ala16, is split. Two cystine disulfide bonds hold together the two peptide chains. The Lys15 of the reactive site is substituted by arginine-, phenylalanine- and valine-4-nitroanilide or by valine-7-amido-4-methylcoumarin. The different incorporated amino acid residues correspond to different specificities against serine proteinases. Serine proteinases with suitable specificity are able to remove 4-nitroaniline or 7-amino-4-methylcoumarin from these aprotinin derivatives while at the same time resynthesis of the reactive-site peptide bond occurs. The proteinase is then trapped in a stable enzyme-inhibitor complex, which prevents the proteinase from releasing further leaving groups. The quantity of 4-nitroaniline or 7-amino-4-methylcoumarin, which can be assayed spectrophotometrically or fluorometrically is equimolar to the quantity of proteinase used and trapped. The aprotinin derivatives with an incorporated Phe15 or Val15 residue are highly specific for chymotrypsin or for elastase from human leukocytes, respectively. The kinetic constants kon and koff of the enzyme-inhibitor complexes, and hence the equilibrium dissociation constants, can be calculated from the respective titration curves.

Alanine↗
PubMed1995

Rhodanese conformational changes permit oxidation to give disulfides that form in a kinetically determined sequence.

When the structure of the monomeric enzyme rhodanese is perturbed by urea or SDS and heat, sulfhydryl assays combined with SDS gel analyses reveal that intrachain disulfides are formed rapidly. Two intrachain disulfide bonded species can be distinguished. One contains a single disulfide and comigrates on SDS gels with fully reduced rhodanese (Band I), while a second species contains two disulfides and migrates faster than the reduced enzyme (Band II). The kinetic path and identity of the participating sulfhydryl groups are suggested by the results with sulfhydryl mutants. On mild oxidation or perturbation, a single disulfide forms that involves two of the three sulfhydryl groups in C-terminal domain of the protein, i.e., two of the sulfhydryl groups from among the three residues: the active-site Cys-247, Cys-254 and Cys-263. These disulfides are the same as those that are formed upon oxidation of the native enzyme. The remaining sulfhydryl group of these three, in a kinetically slower process, can form a disulfide with Cys-63 which is in the N-terminal domain in native rhodanese. The resulting looped structure is so conformationally constrained that its shape and/or altered SDS binding gives rise to the 'fast' Band II on the SDS gels. The conformationally constrained species with two disulfides may be related to oxidized rhodanese species that are difficult to reduce.

Cysteine↗