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Abstract
The Sleeping Beauty (SB) transposase reconstructed from salmonid fish has high transposition activity in mammals and has been a useful tool for insertional mutagenesis and gene delivery. However, the transposition efficiency has varied significantly among studies. Our previous study demonstrated that the introduction of methylation into the SB transposon enhanced transposition, suggesting that transposition efficiency is influenced by the epigenetic status of the transposon region. Here, we examined the influence of the chromatin status on SB transposition in mouse embryonic stem cells. Heterochromatin conformation was introduced into the SB transposon by using a tetracycline-controlled transrepressor (tTR) protein, consisting of a tetracycline repressor (TetR) fused to the Kruppel-associated box (KRAB) domain of human KOX1 through tetracycline operator (tetO) sequences. The excision frequency of the SB transposon, which is the first step of the transposition event, was enhanced by approximately 100-fold. SB transposase was found to be colocalized with intense DAPI (4′,6′-diamidino-2-phenylindole) staining and with the HP1 family by biochemical fractionation analyses. Furthermore, chromatin immunoprecipitation analysis revealed that SB transposase was recruited to tTR-induced heterochromatic regions. These data suggest that the high affinity of SB transposase for heterochromatin conformation leads to enhancement of SB transposition efficiency.
We thank Z. Ivics for providing the anti-SB antibody. We are grateful to M. Kouno, T. Hayakawa, K. Yae, S. Kouno, M. Tachibana, Y. Shinkai, and H. Tojo for their helpful advice and excellent technical support. We thank current members of our laboratory for their support and advice, particularly Y. Odan for her excellent secretarial support.
This work was supported by grants from the New Energy and Industrial Technology Development Organization of Japan; the Cosmetology Research Foundation; RIKEN, the Institute of Physical and Chemical Research; and a grant-in-aid for Science Research from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.