Size-dependent DNA mobility in cytoplasm and nucleus.

Area of Science:

• Cellular and Molecular Biology
• Biophysics
• Gene Therapy

Background:

• DNA diffusion in the cytoplasm is crucial for gene delivery and antisense therapy efficacy.
• Understanding DNA's movement within cells is key to optimizing therapeutic strategies.

Purpose of the Study:

• To quantify the translational diffusion of double-stranded DNA fragments of varying sizes within HeLa cell cytoplasm and nucleus.
• To compare DNA diffusion rates with those of dextrans and to elucidate the factors limiting DNA mobility.

Main Methods:

• Microinjection of fluorescein-labeled double-stranded DNA fragments (21-6000 bp) into HeLa cells.
• Measurement of diffusion coefficients using spot photobleaching with a focused argon laser.
• Comparison of DNA diffusion with fluorescein isothiocyanate (FITC) dextran diffusion.

Main Results:

• DNA diffusion coefficients in aqueous solution decreased with increasing DNA size (21-6000 bp).
• Cytoplasmic DNA diffusion was significantly lower than in aqueous solution, decreasing with size and strongly influenced by molecular crowding.
• DNA fragments (>250 bp) showed markedly reduced diffusion in cytoplasm compared to FITC dextrans.
• DNA fragments were nearly immobile in the nucleus, unlike mobile FITC dextrans.

Conclusions:

• Extensive binding to immobile obstacles restricts DNA diffusion in the nucleus.
• Molecular crowding in the cytoplasm limits the lateral mobility of DNA fragments larger than 250 bp.
• DNA diffusion in the cytoplasm represents a potential rate-limiting barrier for non-viral gene delivery vectors.