The ultrastructure of non-membranous nuclear ghosts

Area of Science:

• Cell Biology
• Molecular Biology
• Biophysics

Background:

• The nuclear envelope's non-membranous components, or nuclear ghosts, are crucial for nuclear structure and function.
• Understanding the composition and organization of these skeletal elements provides insight into nuclear architecture.

Purpose of the Study:

• To characterize the ultrastructure of non-membranous HeLa cell nuclear ghosts using transmission electron microscopy.
• To identify the molecular components and structural organization of these nuclear ghost elements.
• To investigate the role of DNA in maintaining the integrity of nuclear ghosts.

Main Methods:

• Whole-mount transmission electron microscopy of isolated HeLa cell nuclear ghosts.
• Enzymatic digestion (DNase I, DNase II, nuclease S1) to probe structural composition.
• Isolation procedure variations to confirm structural integrity.

Main Results:

• Identified major components: annuli (43/90 nm inner/outer diameter) resembling nuclear pore complexes and rod-like structures (260x50 nm).
• Annular and rod-like structures are interconnected by strands (15-30 nm width).
• Enzymatic assays revealed sensitivity to DNases but resistance to nuclease S1, indicating DNA dependence for structural integrity.
• Similar ghost components and organization were observed across mammals, birds, and plants.

Conclusions:

• HeLa cell nuclear ghosts are non-membranous protein structures with DNA-dependent integrity.
• The observed annuli and rod-like structures represent key nuclear skeletal components, potentially including nuclear pore complexes.
• The findings suggest a conserved structural role for DNA in nuclear ghost organization across diverse species.