Ars insulator protects transgenes from long-term silencing in sea urchin larva

Reporter genes have been used as a powerful tool to analyze cis-regulatory elements responsible for temporal and spatial expression in the early development of sea urchin. However, here we show that the transgenes introduced into the sea urchin embryos undergo suppression in larval stage. The transgene silencing could be one of major obstacle in the analysis of regulatory regions in the late stages of development. We previously demonstrated that a DNA fragment (ArsI) located in the upstream region of sea urchin (Hemicentrotus pulcherrimus) arylsulfatase gene has the property of an insulator. We show that tandem ArsI prevents silencing of a transgene in sea urchin larvae when the ArsI is fused to the 5' end of the reporter gene. Furthermore, we demonstrate that DNA of the reporter gene introduced into the sea urchin eggs is methylated during development and that the ArsI protects the transgene from the DNA methylation.