期刊
ANNUAL REVIEW OF GENETICS, VOL 45
卷 45, 期 -, 页码 227-246出版社
ANNUAL REVIEWS
DOI: 10.1146/annurev-genet-110410-132432
关键词
ciliates; RNAi; PIWI; heterochromatin; DNA rearrangement; transposon
Ciliated protozoa extensively remodel their somatic genomes during nuclear development, fragmenting their chromosomes and removing large numbers of internal eliminated sequences (IESs). The sequences eliminated are unique and repetitive DNAs, including transposase. Recent studies have identified transposase proteins that appear to have been domesticated and are used by these cells to eliminate DNA not wanted in the somatic macronucleus. This DNA elimination process is guided by meiotically produced small RNAs, generated in the germline nucleus, that recognize homologous sequences leading to their removal. These scan RNAs are found in complexes with PIWI proteins. Before they search the developing genome for IESs to eliminate, they scan the parental somatic nucleus and are removed from the pool if they match homologous sequences in that previously reorganized genome. In Tetrahymena, the scan RNAs target heterochromatin modifications to mark IESs for elimination. This DNA elimination pathway in ciliates shares extensive similarity with piRNA-mediated silencing of metazoans and highlights the remarkable ability of homologous RNAs to shape developing genomes.
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