Generation and characterization of mice with mesenchyme-specific deletion of the entire ESET histone methyltransferase protein.

ESET protein (also known as SETDB1) catalyzes methylation of histone H3 at lysine 9 (H3-K9). In addition to the full-length transcript, mouse ESET gene also gives rise to alternative spicing variants encoding truncated proteins capable of retaining interaction with other epigenetic enzymes. To completely eliminate full-length ESET and its splicing variants, we have generated a conditional ESET allele with exon 4 flanked by two loxP sites for Cre-mediated DNA deletion and downstream frame-shift mutation of the entire coding region. Mating with Prx1-Cre mice and analysis of the resultant embryos revealed that mesenchyme-specific knockout of exon 4 completely eliminates full-length ESET and its truncated protein products, leading to profound defects in both the flat bones and long bones, ectopic hypertrophy of growth plate chondrocytes and downregulation of Indian hedgehog protein. In addition, exon 4 deletion results in reduced thickness of articular cartilage in E17.5 embryos, whereas deletion of exons 15-16 fails to do so. These findings offer us a useful tool to further study epigenetic regulation in a truly ESET-null background, and demonstrate that ESET plays a critical role in the control of chondrocyte hypertrophy and skeletal development.

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