snRNA and Heterochromatin Formation Are Involved in DNA Excision during Macronuclear Development in Stichotrichous Ciliates

Volume 4, no. 11, p. 1934-1941, 2005. We reported previously the presence of the histone modification H3K9-methylated H3 (H3K9me3) in the micronucleus of the ciliate Stylonychia. We now realize that the antibodies used in that study cross-react with H3K27me3 in Stylonychia, and the signals observed in the micronucleus were due to this cross-reactivity. By using very specific antibodies it is now clear that H3K27me3 is present in the micronucleus but H3K9me3 becomes introduced de novo into the developing macronucleus.