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Biomedical subjects

J H Gregg

Publications and source records attributed to J H Gregg.

At least 19 recordsLinked to original sources
PubMed1985

Use of a monoclonal antibody recognizing a cell surface determinant to distinguish prestalk and prespore cells of Dictyostelium discoideum slugs.

Double labelling experiments on Dictyostelium discoideum cells at different developmental stages were carried out using monoclonal antibodies MUD1 (prespore specific), MUD9 (strong label on prestalk and anterior-like cells) and a fluorescence-activated cell sorter. The monoclonal antibody MUD9, which recognizes the surface of prestalk and anterior-like cells strongly and prespore cells weakly, is also present on the surface of vegetative amoebae and on mature stalk cells but not on the spore surface. Sharing of an antigenic determinant between vegetative, prestalk and anterior-like cells is consistent with these cells being 'less differentiated' than prespore cells.

Antibodies, Monoclonal↗
PubMed1984

Evidence that positional information is used to establish the prestalk-prespore pattern in Dictyostelium discoideum aggregates.

Two contrasting mechanisms have been proposed for the establishment of the prestalk-prespore pattern in the multicellular aggregate of the simple eukaryote Dictyostelium discoideum. One involves intermingled, non-position-dependent cell differentiation followed by sorting out which produces the pattern of prestalk cells in the anterior region and prespore cells posteriorly. The second mechanism involves patterning according to the position of cells within the aggregate, in which case intermingled cell types are not expected. Here we use a monoclonal antibody (MUD1), recognising a prespore cell surface antigen, to study the initial appearance of prespore cells in aggregates. Quantitative studies were made with a flow cytometer and frozen sections were used to localise the cells expressing the prespore antigen. This antigen first appeared at the onset of tip formation in the centre of aggregates in a position-dependent fashion. The prespore antigen was not detected in the tip region or in streams of cells entering the aggregate. We re-examined the evidence on which the non-position-dependent differentiation model is based. Our results support the positional model for pattern formation.

Journal Article↗
PubMed1982

Antigenic differences detected between prespore cells of Dictyostelium discoideum and Dictyostelium mucoroides using monoclonal antibodies.

A method was developed to obtain frozen sections of paraformaldehyde-fixed Dictyostelium slugs. These sections were ideal for studies using monoclonal antibodies. Two different monoclonal antibodies were used to recognize specific antigens on the surface of D. discoideum prespore cells by fluorescence microscopy. Neither of the two monoclonal antibodies bound to D. discoideum prestalk cells. D. mucoroides, a closely related species to D. discoideum, failed to bind either monoclonal antibody to its prespore cells. These results contrast with those obtained with either D. mucoroides [1] or D. discoideum [2] polyspecific antisera.

Animals↗
PubMed1982

A temperature-dependent choice in cell differentiation.

Ascension of the cell mass during culmination was observed to be temperature-sensitive in strain HH31 of the cellular slime mold Dictyostelium discoideum. A sequence of additional developmental abnormalities was also observed both preceeding and succeeding culmination. Slugs reared at the restrictive temperature (27 degrees C), in contrast to those reared at the permissive temperature (22 degrees C), were deficient in the expression of six prespore markers and elevated in the production of four prestalk markers. Following attempted culmination at the restrictive temperature, the majority of cells were stalk cells according to fluorescence, phase contrast, electron microscopic, biochemical, and plating efficiency criteria. These findings were correlated with a general diminution of staining of slug cell Membrane extracts on polyacrylamide gels with FITC-wheat germ agglutinin. The effect of the higher temperature was readily reversible prior to terminal differentiation. An interdependence of several of the changes was suggested by the observation that in two derivative strains the temperature-dependence of these changes was coordinately altered. In summary, a large fraction of the slug cells of HH31 appear to be temperature-dependent in their choice of pathways of cell differentiation, this change is related to a modification of the cell surface, and the choice made in the slug is remembered by cells as they terminally differentiate.

Cell Differentiation↗
PubMed1978

Cell contact-induced inhibition of division in Dictyostelium.

The developmental stage at which Dictyostelium discoideum strain v12/M2 cells was inhibited in resuming cell division was monitored by a Coulter counter. Neither vegetative nor pre-aggregating v12/M2 amoebae used as inocula in liquid growth cultures exhibited a delay in recommencing cell division. Inocula prepared from aggregates were delayed for 3 h before the onset of division. Although cyclic AMP had no effect upon vegetative or preaggregating stages the aggregating amoebae were inhibited for 9 h before resuming division. Following the onset of division by both controls and cyclic AMP-treated cells the normal growth rate of vegetative amoebae (3.2 h/generation) was attained. Aggregateless mutant vegetative amoebae and those of comparable ages to vas/M2 aggregates were not inhibited in the rate of cell division by cyclic AMP. Cyclic AMP sustains the delay in cell division only among amoebae derived from aggregates. Cyclic AMP induces structural components in the plasma membranes which may be necessary in cell adhesion and interactions. Consequently interactions between the membranes of apposing cells may transmit stimuli intracellularly to inhibit cell division.

Cell Division↗
PubMed1973

Response of Dictyostelium plasma membranes to adenosine 3':5'-cyclic monophosphate.

Myxamoebae of the cellular slime mold Dicytostelium discoideum aggregate in response to a chemotactic substance identified as adenosine 3':5'-cyclic monophosphate. Upon aggregation cell division is suppressed, the cells become adhesive, and differentiation is initiated. Freeze-fracture studies of myxamoebae were conducted to determine the effect of cyclic AMP and calcium on plasma membrane ultrastructure. The inner surfaces of the plasma membranes exhibited particulate structures whose sizes (43-187 A) and frequency distribution were determined. Cyclic AMP and calcium induced within 2 hr the formation of particles having average diameters 1.7-times and 1.5-times greater, respectively, than those of the vegetative myxamoebae controls. These data suggest that cyclic AMP mobilizes the intracellular calcium which may be effective in changing plasma membrane structure.

Calcium↗
PubMed1965

Centrifugal homogenizer.

Tissue can be homogenized in conventional ground-glass tissue grinders in conjunction with centrifugation. The method may be of special value for separating soluble from insoluble material during homogenization of tissue. As yet only yeast cells and spores of slime mold have been homogenized, but the method may be useful for many tissues.

Centrifugation↗