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Membranes of the mitotic apparatus of mammalian cells
Abstract:
HeLa cells in mitosis are fixed by KMnO4 to obtain a good preservation of membranes. Inside and around the mitotic apparatus a vesicular, a tubular and a cisternal type of membranes are demonstrated. Small spherical or ellipsoidal vesicles are distributed at random in the spindle area. Zones around the poles and in the midbody of telophase cells are almost free from vesicles. Elements of the tubular ER are often aggregated in parallel arrays at the periphery of the spindle region, thus resembling dictyosomes. During telophase tubular ER is most prominent at the cleavage furrow. Layers of concentrically arranged flat cisternae surround the spindle region during the middle stages of mitosis. Radiating from the poles such membranes form large asters, thereby interrupting the concentric arrangement. This pattern might act as a barrier against larger cytoplasmic organelles or as a cisternal system to bring about an oriented transport of molecules from or to the poles. Fragments of the two large indentations of the nuclear envelops in prophase are aggregated in the spindle region and later on contribute to form new envelopes around the daughter nuclei.
Insights
This study reveals the membrane structures within HeLa cells during mitosis, detailing the distribution of vesicular, tubular, and cisternal membranes around the mitotic apparatus. These findings offer insights into cellular organization during cell division.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Understanding the dynamic membrane rearrangements during cell division is crucial for comprehending cell cycle regulation.
- The precise roles of different membrane types in mitosis remain incompletely understood.
Purpose of the Study:
- To characterize the types and distribution of membranes within the mitotic spindle apparatus of HeLa cells.
- To investigate the potential functions of these membrane structures during mitosis and telophase.
Main Methods:
- HeLa cells undergoing mitosis were fixed using potassium permanganate (KMnO4) to preserve membrane structures.
- Electron microscopy was employed to visualize and analyze the morphology and distribution of vesicular, tubular, and cisternal membranes.
Main Results:
- Vesicular membranes were observed randomly distributed within the spindle area, with sparse presence at the poles and midbody during telophase.
- Tubular endoplasmic reticulum (ER) elements formed parallel arrays at the spindle periphery and were prominent at the cleavage furrow during telophase.
- Concentric layers of cisternal membranes surrounded the spindle, forming asters radiating from the poles, potentially acting as barriers or transport systems.
Conclusions:
- The study demonstrates distinct membrane configurations, including vesicular, tubular ER, and cisternal types, within the mitotic apparatus of HeLa cells.
- These membrane arrangements suggest roles in organizing the spindle, regulating transport, and potentially contributing to nuclear envelope reformation.
- The findings provide a detailed ultrastructural map of membrane dynamics during mitosis.