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The effects of enucleation on the cytoplasmic membranes of Amoeba proteus
Abstract:
The dependence of cytoplasmic membranes upon the nucleus was studied by examining enucleated amebae with the electron microscope at intervals up to 1 wk after enucleation. Amebae were cut into two approximately equal parts, and the fine structure of the enucleated portions was compared with that of the nucleated parts and starved whole cells which had been maintained under the same conditions. Golgi bodies were diminished in size 1 day after enucleation and were not detected in cells enucleated for more than 2 days. The endoplasmic reticulum of enucleated cells appeared to increase in amount and underwent changes in its morphology. The sparsely scattered short tubules of granular endoplasmic reticulum present in unmanipulated amebae from stock cultures were replaced in 1-3-day enucleates by long narrow cisternae. In 3-7-day enucleates, similar cisternae of granular endoplasmic reticulum encircled areas of cytoplasm partially or completely. It was estimated that in most cases hundreds of these areas encircled by two rough membranes were formed per enucleated cell. The number of ribosomes studding the surface of the endoplasmic reticulum decreased progressively with time after enucleation. In contrast, the membranes of nucleated parts and starved whole cells did not undergo these changes. The possible identification of membrane-encircled areas as cytolysomes and their mode of formation are considered. Implications of the observations regarding nuclear regulation of the form of the Golgi apparatus and the endoplasmic reticulum are discussed.
Insights
The nucleus is crucial for maintaining cytoplasmic membranes in amebae. Enucleation leads to significant changes in the Golgi apparatus and endoplasmic reticulum, indicating nuclear regulation of cell structure.
Area of Science:
- Cell Biology
- Cytology
- Molecular Biology
Background:
- Cytoplasmic membranes are essential for cellular function.
- The nucleus plays a vital role in regulating cellular processes.
- Previous studies suggest a connection between the nucleus and membrane-bound organelles.
Purpose of the Study:
- To investigate the dependence of cytoplasmic membranes on the nucleus.
- To examine the structural changes in enucleated amebae over time.
- To understand the nuclear regulation of Golgi apparatus and endoplasmic reticulum morphology.
Main Methods:
- Enucleation of amebae to create cell fragments without a nucleus.
- Electron microscopy to analyze the fine structure of enucleated and nucleated cell portions.
- Comparison of enucleated cells with nucleated parts and starved whole cells.
Main Results:
- Golgi bodies diminished in size and disappeared within 2 days post-enucleation.
- Endoplasmic reticulum increased in amount and altered morphology, forming long cisternae.
- Ribosome density on the endoplasmic reticulum decreased over time in enucleated cells.
- Membrane-encircled areas, possibly cytolysomes, formed extensively in enucleated cells.
Conclusions:
- The nucleus is essential for maintaining the normal structure of the Golgi apparatus and endoplasmic reticulum.
- Enucleation triggers significant, time-dependent alterations in cytoplasmic membrane systems.
- These findings highlight the critical role of nuclear regulation in cellular membrane homeostasis.