Differences in the efficiency and stability of gene expression after transfection and nuclear injection: A study with a chick .DELTA.-crystallin gene.

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Abstract
The efficiency of an exogenous gene''s expression was compared after its transfection and injection into various mouse cells to systematically evaluate these 2 gene transfer techniques. Special attention was paid to the period of transient expression. The gene used was a derivative of chicken .delta.-crystallin gene with the 5'' end region replaced by a promoter base sequence of a retrovirus. Nuclear injection was more efficient than transfection in several respects: it was roughly 1000 times more efficient in producing gene-expressing cells than the transfection technique; it produced positive cells in every challenged cell line in contrast to the results of some unsuccessful trials found with transfection; and the maximum expresison of the exogenous gene in a gene-transferred cell was much higher after injection than after transfection. With the transfection technique, use of a DNA-calcium phosphate coprecipitate was slightly more efficient than the use of DEAE-dextran. The stability of gene expression in transfected and nuclear-injected cells differed greatly: Expression of the exogenous gene in transfected cells was transmitted to 92% of the daughter cells/division, whereas its expression in injected cells was transmitted to only 32% of the daughter cells. This great difference in stability probably reflects different states of the major fraction of the exogenous gene: integration into chromosomes in transfected cells vs. extrachromosomal localization in injected cells.