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D Ratner

Publications and source records attributed to D Ratner.

33 records · Page 2Linked to original sources
PubMed1983

Comparison of differentiating Dictyostelium discoideum cell types separated by an improved method of density gradient centrifugation.

During the migrating slug stage of development of the cellular slime mold Dictyostelium discoideum, the precursor cells of the mature spores and stalk are known to differ from each other. In order to explore these differences on a variety of levels, we have improved existing methods for the isopyknic purification of the precursor types. Prespore and prestalk amoebae obtained from mechanically dissociated slugs were separated by centrifugation on preformed Percoll density gradients. The isolated precursor cells are greater than 90-95% pure, show good viability and developmental competence, and can be obtained in relatively large amounts. We have performed initial comparisons of the differentiating amoebae with respect to their location within the slug, protein composition, and developmental capabilities. Density centrifugation reveals heterogeneity among posterior slug cells: The majority of these cells have the expected prespore characteristics, but there is also a minor (lighter) density fraction resembling anterior, prestalk amoebae. Thirty polypeptides synthesized preferentially by prespore or prestalk slug cells were detected by two-dimensional gel electrophoresis and fluorography. Some of these proteins are equally cell-specific when their accumulation is measured by silver staining; others are remarkably non-specific when stained. When the isolated precursor populations were allowed to complete development, they differed in terms of developmental territory size and timing, and in ways which suggest differences in cell cohesion and chemotaxis.

Cell Separation↗
PubMed1983

Induction and modulation of cell-type-specific gene expression in Dictyostelium.

We have identified genes that are expressed preferentially in either prestalk or prespore cells in Dictyostelium. The prestalk mRNAs are detectable at 7.5 hr prior to the completion of cell aggregation, while the prespore mRNAs are not detectable until approximately 15 hr of development. Exogenous cAMP in the absence of sustained cell contact is sufficient to induce prestalk-specific gene expression, while multicellularity is required for the induction of prespore-specific genes. A gene expressed equally in both cell types, which has the same developmental kinetics as the prestalk genes, is induced in shaking culture in the absence of either cAMP or stable cell associations. Dissociation of aggregates results in the rapid loss of prespore- and prestalk-specific mRNAs, and these can be induced to reaccumulate with the addition of cAMP. We conclude that there are substantial differences in the timing and requirements for tissue-specific gene expression in Dictyostelium.

Cell Communication↗
PubMed1983

Different synthetic profiles and developmental fates of prespore versus prestalk proteins of Dictyostelium.

Depending upon environmental conditions, developing cells of the cellular slime mold Dictyostelium discoideum may enter a slug stage in which the cell mass migrates in response to gradients of light and temperature. This developmental stage has often been used to study the divergent differentiation of the cells that will subsequently form spores and stalk in the mature fruiting body. However, still debated is the extent to which the differentiation evident in slug cells is a precondition for development of the mature cells in fruits. Using two-dimensional gel electrophoresis of polypeptides, we have examined the proteins made by prespore and prestalk cells of migrating slugs and by maturing spore and stalk cells. The data indicate that many of the cell-type specific polypeptides in prespore cells of slugs persist as cell-type specific polypeptides of mature spores. Prestalk slug cells, in contrast, do not contain significant amounts of stalk-specific proteins; these proteins appear only during culmination. The precursor cell types also differ in the times and rates of synthesis of cell-specific proteins: prestalk proteins appear much earlier in development than do the prespore, but never reach the levels of expression that the prespore proteins do later in culmination. These findings may explain the well established ability of prespore cells to regulate their cell type more rapidly than do prestalk cells. There are also implications for our general understanding of what is a 'prestalk' gene product.

Cell Differentiation↗
PubMed1983

Milk protein-free diet for nonseasonal asthma and migraine in lactase-deficient patients.

In a series of 48 patients suffering from either nonseasonal asthma or classic migraine, a marked clinical alleviation was obtained in 33 patients by removing all cows milk protein from their diet. All patients who responded to the diet had laboratory evidence of lactase deficiency. Lactase deficiency may be a useful indicator of milk allergy in asthmatic or migrainous patients.

Adolescent↗
PubMed1983

Chronic dietary anticholinesterase poisoning.

Five patients presented with chronic gastrointestinal symptoms and nonspecific neurologic complaints, accompanied by reductions in whole blood cholinesterase activity. After the elimination from their diet of fresh fruits and vegetables, the patients became asymptomatic and their blood cholinesterase activity returned to normal levels. The source of this previously unreported type of poisoning is discussed.

Adult↗