During sexual reproduction in the unicellular ciliate Stylonychia somatic macronuclei differentiate from germline micronuclei. Thereby， programmed sequence reduction takes place， leading to the elimination of > 95% of germline sequences， which priorly adopt heterochromatin structure via H3K27me3. Simultaneously， 27nt-ncRNAs become synthesized from parental transcripts and are bound by the Argonaute protein PIWI1.