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W F Loomis

Publications and source records attributed to W F Loomis.

At least 109 records · Page 6Linked to original sources
PubMed1983

Adhesion-blocking antibodies prepared against gp150 react with gp80 of Dictyostelium.

A membrane glycoprotein of 150 000 D, gp150, has been implicated in the mechanism of cell-cell adhesion which arises during development of Dictyostelium discoideum. This conclusion was founded on the observation that monovalent Fab' fragments prepared from an antiserum raised against partially purified gp150 are able to block cell-cell adhesion. We show that this serum contains antibodies to a distinct membrane glycoprotein, gp80, previously implicated in cell-cell adhesion. Reaction of Fab' to this surface molecule can account for the adhesion-blocking activity in the antiserum to gp 150. Moreover, binding of gp80 neutralized Fab' to gp150 does not block adhesion. If gp150 carries other determinants which bind adhesion-blocking Fab', these determinants must also be present on gp80. Thus, it is not clear that gp150 is directly involved in cell-cell adhesion of Dictyostelium.

Antibodies↗
PubMed1983

Monoclonal antibody recognizing gp80, a membrane glycoprotein implicated in intercellular adhesion of Dictyostelium discoideum.

WE have raised a monoclonal antibody, designated E28D8, which reacts with an 80,000-dalton membrane glycoprotein (gp80) of Dictyostelium discoideum. gp80 has been implicated in the formation of the EDTA-resistant adhesions ("contact sites A") which appear during development. The monoclonal antibody reacted with other developmentally regulated proteins of D. discoideum, confirming previous results indicating the presence of common antigenic determinants recognized by polyclonal rabbit antibodies directed to gp80. Periodate sensitivity of the determinants suggests that carbohydrate may be necessary for reactivity. Thus, the determinant recognized by E28D8 may result from a posttranslational modification common to a number of proteins. Some of the proteins that carry the determinant were preferentially localized to posterior cells in slugs. Monoclonal antibody E28D8 did not inhibit contact-sites-A-mediated intercellular adhesion. However, gp80 affinity purified on immobilized monoclonal antibody was able to neutralize the adhesion-blocking effect of rabbit antiserum to gp80. Although gp80 itself may not be essential for cell-cell adhesion, it appears to carry the determinants associated with adhesion.

Antibodies, Monoclonal↗
PubMed1982

Differential synthesis of spore coat proteins in prespore and prestalk cells of Dictyostelium.

The major spore coat proteins (SP60, SP70, and SP96) of Dictyostelium discoideum have been analyzed by using two-dimensional nonequilibrium pH gradient electrophoresis. These proteins have been characterized with respect to electrophoretic behavior, metachromatic staining with silver, and posttranslational modifications; these techniques allow unambiguous identification of these proteins in silver-stained gels and autofluorograms of total cell extracts. They are synthesized by cells in the prespore region of migrating slugs, ultimately becoming major components of mature spores, but are not detectable either in cells in the prestalk region of slugs or in mature stalk cells. The ease with which these relatively abundant proteins can be recognized on two-dimensional gels makes them very useful markers for spatial and temporal differentiation in this organism.

Cell Differentiation↗
PubMed1982

Phosphorylation of the major heat shock protein of Dictyostelium discoideum.

The major heat shock protein, hsp 70, of Dictyostelium discoideum was found to be rapidly phosphorylated. Analysis of [35S]methionine- and 32Pi-labeled hsp 70 revealed that two similar but distinct proteins of about 70,000 daltons each are synthesized at a high rate after a heat shock, and that each has a phosphorylated member. The phosphorylation chiefly modifies threonine residues. Rapid turnover of the phosphate group occurs, resulting in a steady-state condition in which only about half of the hsp 70 is phosphorylated at a given time.

Cycloheximide↗
PubMed1981

Immunological analysis of glycoprotein (contact sites A) involved in intercellular adhesion of Dictyostelium discoideum.

We have prepared antisera in rabbits to the "contact sites A" glycoprotein (gp80) purified from Dictyostelium discoideum. IgG isolated these antisera reacts with a number of different proteins in D discoideum lysates, as analyzed by immune precipitation and by antibody staining of gel electropherograms transferred to nitrocellulose. blocking experiments indicate that this cross-reactivity reflects the presence of common antigeneic determinants on gp80 and other cellular proteins, rather than the presence of extraneous antibodies in the antisera. The spectrum of reactive proteins is different at different stages of development. In particular, gp80 itself is synthesized only for a restricted period during the cell aggregation phase. The protein persists throughout development and can be detected in spores. Anti-gp80 Fab fragments bind to the surface of developing D discoideum cells and specifically block their developmentally regulated adhesion. After absorption with vegetative cells, the IgG stains only gp80 and (to a lesser extent) one other band in lysates of aggregation-competent cells. The absorbed antibodies also can block adhesion. Several proteins that appear late in development also are stained by the absorbed IgG.

Antigen-Antibody Complex↗
PubMed1980

Attempts to isolate mutants of Dictyostelium discoideum which express alpha-mannosidase-2 constitutively.

Evidence was sought for a gene-specific negative regulatory element of Dictyostelium discoideum similar to the repressor/operator systems that control some operons in prokaryotes and their viruses. Mutants of D. discoideum that constitutively express the stage-specific enzyme alpha-mannosidase-2 could provide such evidence. Reconstruction experiments demonstrated that the screening technique developed would detect mutants of that type. Over 2 x 10(5) survivors of heavily mutagenized cell populations were grown and their progeny tested. No mutants of the desired type were obtained. The possible implications of this finding are discussed.

Dictyostelium↗
PubMed1978

Characterization and genetic mapping of modA. A mutation in the post-translational modification of the glycosidases of Dictyostelium discoideum.

We have isolated a mutant of Dictyostelium discoideum, M31, which produces a reduced number of alpha-mannosidase-1 molecules per cell during the developmental program of the organism. We find that several of the glycosidases, a group of lysosomal proteins produced by D. discoideum, are altered in strain M31 and that this strain produces a reduced level of at least three of these activities. These enzymes do not share a common protein subunit but are known to share a common antigenic determinant which is, in part, carbohydrate in nature. In the wild type parent of M31, alpha-mannosidase-1 is modified by the addition of mannose and glucosamine (probably as N-acetylglucosamine) in the molar ratio of 5:2. alpha-Mannosidase-1 was also found to contain phosphoserine/phosphothreonine residues. alpha-Mannosidase-1 and other glycosidases are electrophoretically less negative when isolated from strain M31 than when isolated from wild type cells. The mutation present in M31, modA, appears to affect posttranslational modification, modA is a recessive mutation which we map onto linkage group I.

Amino Acids↗
PubMed1978

Chemical analysis of stalk components of Dictostelium discoideum.

Structural components of the stalks of mature fruiting bodies of Dictyostelium discoideum have been isolated and characterized after solubilizing non-structural components with urea and sodium dodecyl sulfate. The urea/sodium dodecyl sulfate-insoluble stalks are composed of about 52% cellulose, 15% protein and 3% of a non-cellulosic heteropolymer in a covalently bound matrix. Non-covalently bound fatty acid containing material was also found. The composition and structural interrelationships of these components are essentially identical to that of the urea/sodium dodecyl sulfate-insoluble surface sheath which is produced earlier in development before culmination. These results suggest that the same components are involved in making structural elements which differ substantially in their functional role in the developmental sequence as well as in their spatial and temporal localization and morphological appearance.

Amino Acids↗