Search PubMed⌕ Search

Biomedical subjects

S Benson

Publications and source records attributed to S Benson.

At least 19 recordsLinked to original sources
PubMed1997

Adaptive mutation: a general phenomenon or special case?

A recent article by Galitski and Roth characterizes adaptive reversion of chromosomal lac- mutations in Salmonella typhimurium LT2. Using a classical genetic approach they show that adaptive reversion, as characterized by the appearance of late revertant colonies, is an exception rather than a general phenomenon for reversion of nonsense, missense, frameshift and insertion mutations. For certain mutations, however, the number of late revertants exceeds the predicted number. These excess revertants suggest that adaptive mutability is applicable to chromosomal genes as well as to genetic changes involving F plasmids and lysogenic phages.

Adaptation, Physiological↗
PubMed1995

Myoblast transfer in the treatment of Duchenne's muscular dystrophy.

BACKGROUND: Myoblast transfer has been proposed as a technique to replace dystrophin, the skeletal-muscle protein that is deficient in Duchenne's muscular dystrophy. Donor myoblasts injected into muscles of affected patients can fuse with host muscle fibers, thus contributing their nuclei, which are potentially capable of replacing deficient gene products. Previous controlled trials involving a single transfer of myoblasts have been unsuccessful. METHODS: We injected donor muscle cells once a month for six months to the biceps brachii muscles of one arm of each of 12 boys with Duchenne's muscular dystrophy. The opposite arms served as sham-injected controls. In each procedure 110 million cells donated by fathers or brothers were transferred. The patients were randomly assigned to receive either cyclosporine or placebo. Strength was measured by quantitative isometric muscle testing. Six months after the final myoblast transfer, the presence of dystrophin was assessed with the use of peptide antibodies specific to the deleted exons of the dystrophin gene. RESULTS: There was no significant difference in muscle strength between arms injected with myoblasts and sham-injected arms. In one patient, 10.3 percent of muscle fibers expressed donor-derived dystrophin after myoblast transfer. Three other patients also had a low level of donor dystrophin (< 1 percent); eight had none. CONCLUSIONS: Myoblasts transferred once a month for six months failed to improve strength in patients with Duchenne's muscular dystrophy. The value of exon-specific peptide antibodies in the interpretation of myoblast-transfer results was demonstrated in a patient with Duchenne's muscular dystrophy who had a high percentage of donor-derived dystrophin. Specific variables affecting the efficiency of myoblast transfer need to be identified in order to improve upon this technique.

Antibodies↗
PubMed1995

Characterization and localized expression of the laminin binding protein/p40 (LBP/p40) gene during sea urchin development.

We have isolated and characterized the expression of a cDNA clone from the sea urchin Strongylocentrotus purpuratus that encodes a protein very similar to LBP/p40, originally identified as a nonintegrin, 67-kDa laminin binding protein. The deduced amino acid sequence of the protein, which we call spLBP/p40, shows significant similarity with the LBP/p40 from other sources, although significant divergence does occur at the carboxyl end. The S. purpuratus mRNA is present as a maternal transcript and its level remains constant until activation of zygotic transcription at the hatching blastula stage, whereupon the total spLBP/p40 increases through the pluteus larval stage. Adult tissues also contain the spLBP/p40 mRNA. Both maternal and zygotic transcripts are translated as determined by their presence in polysomes. Immunoblot analysis using an antibody raised against a recombinant fusion protein indicates that the concentration of the spLBP/p40 protein remains constant during development despite the postblastula increase in mRNA concentration. However, the spatial distribution of the protein changes from a uniform, intracellular distribution in all cells of cleavage and blastula stages to localized, elevated levels in cells of the gut, primary mesenchyme, and oral epithelium of prism larvae. The distribution of spLBP/p40 mRNA at different developmental stages, analyzed by in situ hybridization, reflects that of the protein. Our results argue against a laminin binding function for this protein; instead they place the spLBP/p40 gene in a class of previously described sea urchin genes involved in growth and proliferation.

Amino Acid Sequence↗
PubMed1994

Probing the structure of bacteriophage phi 29 prohead RNA with specific mutations.

Bacteriophage phi 29 of Bacillus subtilis packages its double-stranded DNA genome into a preformed prohead in an ATP-dependent reaction. A 174-residue phi 29-encoded RNA molecule (pRNA) is a structural component of the prohead and is essential for DNA packaging. The secondary and tertiary structures of the prohead binding site on pRNA have been probed using a series of specific mutant pRNAs and by measuring binding to RNA-free proheads and in vitro packaging of the DNA-gene product 3 (DNA.gp3) complex. A pseudoknot in pRNA inferred from phylogenetic studies was confirmed with specific mutations, and this pseudoknot was necessary for DNA.gp3 packaging activity. pRNA was truncated progressively from the 5' and 3' ends to isolate the prohead binding site, and three truncated pRNAs of 79, 71, and 62 residues retained prohead binding activity but could not reconstitute proheads for DNA.gp3 packaging. Mutation resulting in changes of the D hairpin loop and its connecting residues within the prohead binding site of pRNA and DNA packaging studies demonstrated that some alteration of secondary structure in this helix was permissible. The analyses provided further confirmation of a discrete prohead binding domain in pRNA and further delineated specific structural requirements for DNA.gp3 packaging activity which may not be required for prohead binding.

Bacillus Phages↗
PubMed1993

Gram-negative meningitis and chronic constipation: an unusual presentation of caudal regression syndrome.

Congenital malformations may present as meningitis caused by enteric organisms, but this is extremely rare and occurs almost exclusively in the paediatric population. We report an unusual case of a young man with chronic constipation presenting with spontaneous Gram-negative meningitis due to an underlying congenital spinal malformation known as the caudal regression syndrome.

Abnormalities, Multiple↗
PubMed1993

Effects of ciglitazone on blood pressure and intracellular calcium metabolism.

Ciglitazone is the prototype of the thiazolidinedione class of compounds currently being developed for the treatment of insulin resistance and non-insulin-dependent diabetes. The effects of thiazolidinediones on blood pressure and cell calcium metabolism are not well defined. In the obese Zucker rat, a widely studied model of insulin resistance associated with mild hypertension, we investigated the effects of ciglitazone on plasma insulin levels and mean arterial pressure. We also evaluated the effects of ciglitazone on the changes in cytosolic calcium induced by platelet-derived growth factor in A172 human glioblastoma cells and rat A10 vascular smooth muscle cells. Oral administration of ciglitazone, approximately 45 mg/kg per day for 4 weeks, induced significant reductions in plasma insulin levels (p < 0.001) and blood pressure (p < 0.05). Ciglitazone was also found to significantly attenuate the capacity of platelet-derived growth factor BB homodimer to induce sustained increases in intracellular free calcium. These findings suggest that thiazolidinediones may offer a novel pharmacological approach to the treatment of hypertension, and raise the possibility that these compounds may affect blood pressure not only by affecting insulin metabolism but also by modifying the cell calcium response to pressor agents, growth factors, or both.

Animals↗
PubMed1992

Analysis of competence in cultured sea urchin micromeres.

Sea urchin embryo micromeres form the primary mesenchyme, the skeleton-producing cells of the embryo. Almost nothing is known about nature and timing of the embryonic cues which induce or initiate spicule formation by these cells. A related question concerns the competence of the micromeres to respond to the cues. To examine competence in this system we have exposed cultured sea urchin micromeres to an inducing medium containing horse serum for various periods of time and have identified a period when micromeres are competent to respond to serum and form spicules. This window, between 30 and 50 h after fertilization, corresponds to the time when mesenchyme cells in vivo are aggregating and beginning to form the syncytium in which the spicule will be deposited. The loss of competence after 50 h is not due to impaired cell health since protein synthesis at this time is not significantly different from controls. Likewise the accumulation of a spicule matrix mRNA (SM 50) and a cell surface glycoprotein (msp 130), both indices of micromere/mesenchyme differentiation, still occurs in cells that have lost competence to respond to serum by forming spicules. These experiments demonstrate that the acquisition and loss of competence in these cells are regulated developmental events and establish an in vitro system for the identification of the molecular basis for inductive signal recognition and signal transduction.

Animals↗
PubMed1991

Role of the extracellular matrix in tissue-specific gene expression in the sea urchin embryo.

The role of extracellular matrix (ECM) in the differentiation of tissue types was examined in embryos of Strongylocentrotus purpuratus. We have examined the expression of various tissue-specific molecular markers after disrupting the ECM by culturing embryos in the presence of beta-aminoproprionitrile fumarate (BAPN), which disrupts collagen deposition, and beta-D-xyloside, which disrupts proteoglycan metabolism. The markers examined included accumulation of primary mesenchyme-specific mRNA (SM 50); an aboral ectoderm-specific mRNA (Spec 1); and a gut-specific enzyme, alkaline phosphatase. Treatment with BAPN or beta-D-xyloside results in developmental arrest at the mesenchyme blastula stage. Although spicule formation is inhibited, the accumulation of SM 50 transcripts and the synthesis of most of the prominent spicule matrix proteins is similar to that of control embryos. Spec 1 mRNA, in contrast, while accumulating to a significant extent when collagen and proteoglycan metabolism is disrupted, does accumulate to a level somewhat lower than that seen in control embryos. Additionally, the postgastrula rise in gut-specific alkaline phosphatase is reversibly inhibited by BAPN and xyloside treatment. These results demonstrate a differential effect of the ECM on expression of tissue-specific molecular markers.

Alkaline Phosphatase↗
PubMed1991

Primary mesenchyme cells of the sea urchin embryo require an autonomously produced, nonfibrillar collagen for spiculogenesis.

A collagen molecule in the sea urchin embryo was characterized by analysis of a 2.7-kb cDNA clone. This clone, Spcoll, was obtained by screening a gastrula stage Strongylocentrotus purpuratus cDNA library with a 237-bp genomic clone encoding a collagen-like sequence previously isolated by Venkatesan et al. (1986). DNA sequence analysis of the cDNA clone demonstrated the nonfibrillar nature of the encoded molecule--13 interruptions of the Gly-X-Y repeat motif were found in the 85-kDa open reading frame. The mRNA of approximately 9 kb accumulated specifically in mesenchyme cells of the embryo through development to the pluteus larva. Polyclonal antibodies generated against a Spcoll-beta-galactosidase fusion protein were utilized to identify and localize the native Spcoll. This collagen molecule of approximately 210 kDa was deposited into the blastocoel by the primary mesenchyme cells. When primary mesenchyme cells were cultured in vitro, Spcoll was secreted into the media and accumulated at sites of cell-substrate interaction. Addition of anti-Spcoll antibodies to primary mesenchyme cell cultures selectively inhibited spiculogenesis, whereas other antibodies had no inhibitory effect. Since collagen is not a component of the organic matrix of spicules (Benson et al., 1986), these results suggest that the autonomous production of Spcoll by differentiating mesenchyme cells in turn influences the point in differentiation at which these cell initiate biomineralization.

Amino Acid Sequence↗
PubMed1990

The synthesis and secretion of collagen by cultured sea urchin micromeres.

Circumstantial evidence in several previous studies has suggested that sea urchin embryo micromeres, the source of primary mesenchyme cells which produce the embryonic skeleton, contribute to the extracellular matrix of the embryo by synthesizing collagen. A direct test of this possibility was carried out by culturing isolated micromeres of the sea urchin Stronglyocentrotus purpuratus in artificial sea water containing 4% (v/v) horse serum. Under these conditions the micromeres divide and differentiate to produce spicules with the same timing as intact embryos. Collagen synthesis was determined by labeling cultures with [3H]proline or [35S]methionine and the medium and cell layer were assayed for collagen. The results indicate that by the second day in culture micromeres synthesize and secrete a collagenase-sensitive protein doublet with a molecular weight of about 210 kDa. Densitometry indicates a 2:1 ratio of the respective bands in the doublet which is characteristic of Type I collagen. The doublet is insensitive to digestion with pepsin. This differential sensitivity is characteristic of collagen. Over 90% of the collagen synthesized by micromeres is soluble in the seawater culture medium. On days 2-4 in culture, collagen accounts for 5% of the total protein synthesized and secreted. Additional collagenase-sensitive bands are noted at 145 and 51 kDa. The relationship of the described collagen metabolism to previously characterized collagen gene expression in sea urchin embryos is discussed.

Animals↗
PubMed1989

Assessment of the genotoxicity of calcium cyclamate and cyclohexylamine.

Calcium cyclamate and its major metabolite cyclohexylamine have been subjected to numerous evaluations for genetic activity. With the exception of studies for chromosome damage, the results have been negative. Results from a wide range of in vitro and in vivo cytogenetic assays ranged from clearly negative to various degrees of clastogenicity. Interpretation of the cytogenetic studies has been complicated by the conflicting responses, although some of the positive effects seem to be the consequence of secondary effects produced by high ion levels and excessive toxicity. In the studies presented here calcium cyclamate and cyclohexylamine were tested for mutagenic activity using an in vitro mammalian cells assay for gene mutation and an in vitro unscheduled DNA synthesis assay in rat hepatocytes with the Drosophila sex-linked recessive lethal assay. Calcium cyclamate was not genetically active in any of the three assays when tested to the maximum possible concentrations. The compound was largely nontoxic but did show some evidence of cytotoxicity in rat hepatocytes at concentrations of 1 mg/ml and higher. Cyclohexylamine was also negative in the three assays, but was considerably more cytotoxic at the concentrations used. The results from the three studies conducted in this evaluation are in general agreement with the majority of published genetic toxicology data for these two chemicals and indicated that the calcium cyclamate and cyclohexylamine have no direct, intrinsic genotoxicity of the type measured by these assays.

Animals↗
PubMed1989

Expression of an embryonic spicule matrix gene in calcified tissues of adult sea urchins.

The sea urchin spicule is composed of CaCO3 associated with an organic matrix containing at least 10 proteins. We have previously shown that one of these proteins, a 50-kDa glycoprotein (SM 50), is encoded by a gene which is only transcribed in cells of the micromere-mesenchyme lineage. In this report we examined RNA from five adult tissues: ovary, coelomocytes, intestine, tube feet, and spine for the presence of SM 50 transcripts and protein. Only RNA from cells of spine and tube feet hybridized to a SM 50-specific probe on Northern blots. These same two tissues undergo biomineralization and contain a protein which is immunologically related to the SM 50 protein. The restricted accumulation of SM 50 transcripts and protein suggests that the differentiation of biomineralizing mesenchyme cells in embryonic and adult tissue may utilize the same genetic program.

Animals↗