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Expansion and apparent fluidity decrease of nuclear membranes induced by low Ca/Mg. Modulation of nuclear membrane
The Journal of Cell Biology
|November 1, 1978
Summary
Changes in calcium and magnesium ion concentrations alter Tetrahymena macronuclear size by affecting nuclear envelope expansion and lipid fluidity. The nuclear matrix influences these ion-mediated changes in nuclear membrane structure and lipid organization.
Area of Science:
- Cell Biology
- Biochemistry
- Biophysics
Background:
- The structure and function of the nuclear envelope are crucial for eukaryotic cell viability.
- The influence of divalent cations (Ca/Mg) on nuclear envelope dynamics and lipid organization is not fully understood.
- The role of the nuclear matrix in modulating nuclear membrane properties requires further investigation.
Purpose of the Study:
- To investigate the effects of Ca/Mg ion concentrations on Tetrahymena macronuclear size and morphology.
- To elucidate the impact of ion concentration on nuclear envelope structure, including pore complex frequency and membrane lipid properties.
- To explore the potential role of the nuclear matrix in mediating these ion-induced changes.
Main Methods:
- Isolation of Tetrahymena macronuclei and manipulation of Ca/Mg ion concentrations.
- Electron microscopy (thin-sectioning and freeze-etch) to assess nuclear envelope integrity and pore complex density.
- Electron spin resonance (ESR) spectroscopy with 5-doxylstearic acid to determine lipid fluidity and lipid clustering.
Main Results:
- Lowering Ca/Mg concentration from 5 mM to 1 mM induced macronuclear swelling (10.2 to 12.2 micron diameter) with decreased nuclear pore complex frequency.
- Expanded nuclear membranes exhibited reduced particle-devoid areas and increased lipid fluidity compared to contracted membranes.
- Thermotropic lipid clustering occurred in expanded membranes around 17°C, while nuclear membrane lipids rigidified with increasing Ca/Mg concentration.
Conclusions:
- The nuclear matrix's peripheral layer appears to modulate nuclear membrane lipid distribution and fluidity in response to Ca/Mg ion concentrations.
- Contraction of the nuclear matrix may induce nuclear membrane contraction, leading to lateral lipid segregation.
- These findings suggest a mechanism by which the nuclear matrix regulates nuclear envelope structure and dynamics.