Developmental genome rearrangements in ciliates: a natural genomic subtraction mediated by non-coding transcripts.
Several classes of non-protein-coding RNAs have recently been identified as epigenetic regulators of developmental genome rearrangements in ciliates, providing an interesting insight into the role of genome-wide transcription. In these unicellular eukaryotes, extensive rearrangements of the germline genome occur during the development of a new somatic macronucleus from the germline micronucleus. Rearrangement patterns are not dictated by the germline sequence, but reproduce the pre-existing rearrangements of the maternal somatic genome, implying a homology-dependent global comparison of germline and somatic genomes. We review recent evidence showing that this is achieved by a natural genomic subtraction, computed by pairing interactions between meiosis-specific, germline scnRNAs (small RNAs that resemble metazoan piRNAs) and longer non-coding transcripts from the somatic genome. We focus on current models for the RNA-based mechanisms enabling the cell to recognize the germline sequences to be eliminated from the somatic genome and to maintain an epigenetic memory of rearrangement patterns across sexual generations.
Duharcourt
Sandra
S
Ecole Normale Supérieure, Laboratoire de Génétique Moléculaire, 75005 Paris, France. Sandra.Duharcourt@ens.fr
Lepère
Gersende
G
Meyer
Eric
E
D000818:Animals; D016798:Ciliophora / Q000235:genetics* / Q000254:growth & development*; D044127:Epigenesis, Genetic; D015321:Gene Rearrangement; D016678:Genome / Q000235:genetics*; D005854:Germ Cells / Q000378:metabolism; D022661:RNA, Untranslated / Q000235:genetics*
D022661:RNA, Untranslated