The Role of the Plasma Membrane in the Development of the Cellular Slime Mold, Dictyostelium discoideum

Author: Hoffman, Stanley Roy

Year: 1978

Degree: Dissertation (Ph.D.)

Advisor: McMahon, Daniel

Committee Members: McMahon, Daniel; Owen, Ray David; Bonner, James Frederick; Revel, Jean-Paul; Horowitz, Norman Harold

Option: Biology

DOI: 10.7907/d3tj-m764

Abstract

In order to evaluate the role of the plasma membrane in the development of the cellular slime mold, Dictyostelium discoideum, plasma membrane composition and topography were studied in wild type (A3) cells and cells inhibited in development including cells of an aggregation minus mutant, HM 2, with abnormal cellular interactions. One molecule of particular interest, glycoprotein E, was purified and transferred from A3 cells to HM 2 cells and vice versa in order to study the feasibility of experimentally altering plasma membrane composition .

The plasma membrane polypeptide composition and topography of vegetative A3 and HM 2 cells are very similar. However, more sensitive probes can detect several differences between A3 and HM 2. Differences were found between vegetative A3 and HM 2 plasma membranes in antigenic macromolecules, Concanavalin A (Con A) receptors, periodic acid Schiff (PAS) positive glycoproteins, and a glycolipid . Glycoprotein E was aberrant in HM 2 both antigenically and as a Con A receptor. Three PAS positive glycoproteins, including glycoprotein E, were more sensitive to protease treatment of HM 2 than A3 plasma membranes.

Purified glycoprotein E is homogeneous on SDS gels, forms a broad band during isoelectric focusing, and contains a high level of polar amino acids. Glycoprotein E in lipid vesicles is differentially incorporated by A3 and HM 2 cells. The site of glycoprotein E incorporation is the plasma membrane of target cells as demonstrated by indirect immunofluorescence. This study also indicated that this antigenic form of glycoprotein Eis not uniformly exposed on the surface of all A3 cells.

The plasma membrane macromolecular composition and topography of A3 cells changes during development. Forty percent of the polypeptides and ninety-five percent of the glycoprotein species change in amount present during development to preculmination. About 15 cell surface polypeptides were detected at various stages of development, several of which apparently change their topographical location during development.

When development is inhibited by the use of HM 2 cells or cycloheximide treatment of A3 cells, most developmental changes in plasma membrane composition and in polypetide topography were also blocked. In addition, unexpected changes in plasma membrane composition and topography occurred. For example, in inhibited cells, several glycoproteins were more sensitive to pronase treatment of isolated membranes than in A3 cells. Cycloheximide treatment caused the unexpected disappearance of several cell surface polypeptides from the plasma membrane. Although cycloheximide treatment was most effective in blocking developmental changes in plasma membrane composition, the HM 2 mutation had a greater effect on the disruption of plasma membrane topography.

Therefore, these studies indicate that several changes in plasma membrane composition and topography appear to be an integral part of development. Furthermore, in the HM 2 mutant, defects in the plasma membrane even before the initiation of development are correlated with abnormal cellular interactions. Lastly, the feasibility of studying the role of the plasma membrane in development by experimentally altering plasma membrane composition has been demonstrated.

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