Evaluation of nuclear transfer and transcription of plasmid DNA condensed with protamine by microinjection: The use of a nuclear transfer score

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Abstract
In the present study, the nuclear delivery of a green fluorescence protein (GFP)‐encoding pDNA condensed by protamine was investigated in terms of trans‐gene expression after cytoplasmic (E(cyt)) and nuclear (E(nuc)) microinjection. To compare the nuclear transfer process, a novel parameter; the nuclear transfer (NT) score was introduced. The E(cyt) value for protamine/pDNA particles increased in a charge ratio‐dependent manner. The calculated NT score showed that this increase results from an enhancement in nuclear transfer efficiency, which was also quantitatively confirmed by a recently developed confocal image‐assisted three‐dimensionally integrated quantification (CIDIQ) method. Moreover, E(nuc) for protamine/pDNA particles was significantly higher than that for poly‐l‐lysine/pDNA particles, suggesting that pDNA, when condensed with protamine, is more accessible to intra‐nuclear transcription. Collectively, protamine is an excellent DNA condenser, with bi‐functional advantages: improvement in nuclear delivery and efficient intra‐nuclear transcription.