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Electron-microscope study of Dictyostelium discoideum plasma membrane and its modifications during and after
Abstract:
The study of plasma membrane and phagosome membrane of Dictyostelium discoideum was performed using 2 lectins: concanavalin A (Con A) and Wheat Germ Agglutinin (WGA), and 2 markers of anionic sites: colloidal iron hydroxide (CIH) and cationized ferritin (CF). These labellings were applied to fixed partially broken cells, which had ingested a large quantity of yeast. They showed that Con A and CF labelled both the outer and inner faces of the plasma membrane, whereas CIH and WGA were deposited on the outer face only. Phagosome membranes displayed the same location as the plasma membrane for Con A, CF and CIH even in very old phagosomes. This suggests that most receptors of these 3 markers were not degraded by hydrolases. In contrast, phagosome membranes of young and old phagosomes did not react with WGA. When labellings were made on yeast phagocytozing cells, the membrane of phagocytic cups were also devoid of WGA, while it was labelled with the 3 other markers. The absence of WGA labelling was not observed during ingestion of bacteria and latex beads, suggesting a specific relationship existed between yeast cells and WGA receptors.
Insights
Dictyostelium discoideum cells were studied using lectins and anionic site markers. Yeast ingestion revealed specific WGA receptor interactions on phagosome membranes, suggesting unique yeast cell recognition.
Area of Science:
- Cell Biology
- Biochemistry
- Microbiology
Background:
- Understanding the molecular interactions during phagocytosis is crucial for cell biology.
- The plasma and phagosome membranes of Dictyostelium discoideum are key sites for cellular processes.
- Investigating receptor-ligand interactions provides insights into cellular recognition mechanisms.
Purpose of the Study:
- To investigate the distribution and fate of specific membrane receptors during phagocytosis in Dictyostelium discoideum.
- To differentiate the behavior of concanavalin A (Con A), Wheat Germ Agglutinin (WGA), colloidal iron hydroxide (CIH), and cationized ferritin (CF) markers on plasma and phagosome membranes.
- To explore potential specific interactions between yeast cells and WGA receptors during phagocytosis.
Main Methods:
- Labeling of fixed, partially broken Dictyostelium discoideum cells that had ingested yeast.
- Application of two lectins: concanavalin A (Con A) and Wheat Germ Agglutinin (WGA).
- Use of two anionic site markers: colloidal iron hydroxide (CIH) and cationized ferritin (CF).
Main Results:
- Con A and CF labeled both outer and inner plasma membrane faces; CIH and WGA labeled the outer face only.
- Phagosome membranes retained Con A, CF, and CIH labeling, indicating receptor stability.
- WGA did not label phagosome membranes or phagocytic cups during yeast ingestion, unlike other markers, suggesting specific yeast-WGA receptor interactions.
Conclusions:
- Most receptors for Con A, CF, and CIH are resistant to degradation within phagosomes.
- The absence of WGA labeling during yeast phagocytosis suggests a specific interaction or exclusion mechanism.
- This specific WGA interaction is unique to yeast ingestion, not observed with bacteria or latex beads, highlighting a specialized recognition event.