Evaluation of heterologous insulator function with regard to chromosomal position effect in the mouse blastocyst and fetus.

Insulators are located at the boundaries of differentially regulated genes and delimit their interactions by establishing independent chromatin structures. Recently, an insulator sequence has been found in the 5'-flanking region of arylsulfatase (ARS) gene from sea urchin. To investigate functional conservation of this ARS insulator in mice, we performed blastocyst assays to evaluate the effect of this insulator on the chromosomal position effect, quantitatively. We constructed transgenes that have a luciferase gene under the control of the CMV-IE enhancer and the human elongation factor 1 alpha promoter in the presence or absence of the ARS insulator in both flanking regions. These transgenes were microinjected into 1-cell mouse embryos and luciferase activity was measured at the blastocyst stage. We found that the presence of ARS insulator sequence doubled the number of luciferase-expressing blastocysts, and that the proportion of the blastocysts with high-level expression (> or = 1 x 10(4) relative light units (RLU)) was increased more than tenfold. In the case of transgenic fetuses, however, the presence of ARS insulator did not seem to improve transgene expression. These results suggest that the sea urchin ARS insulator confers position-independent expression driven by the human elongation factor 1 alpha promoter, at least in the blastocyst stage of the mouse.