Paramecium tetraurelia autogamy series 2 (ND7-silenced and control cells)

P. tetraurelia, like all ciliates, is a unicellular eukaryote processing two different kinds of nuclei, germline micronuclei (mic) and somatic macronucleus (mac). The diploid micronuclei undergo meiosis during sexual events to transmit the germline genome to the next generation. The highly polyploid mac (~800 n) is responsible for transcription during the life cycle but is lost after fertilisation; the new mic and mac develop from mitotic copies of the zygotic nucleus. During development of the new mac, the germline genome is amplified from 2n to ~800n and is extensively rearranged by two distinct kinds of DNA elimination. The micronuclear 50 to 60 Chromosomes are fragmented into ~200 shorter molecules caped by de novo telomere addition as a result of the imprecise elimination transposons and minisatellites. Moreover, approximately 60,000 short, single-copy elements called internal eliminated sequences (IESs) are precisely removed from coding and non-coding sequences. It was shown that the rearrangements in the developing mac appear to reproduce the rearrangements observed in the old mac, implying the existence of homology dependent cross talk between germline and somatic genomes during sexual event. To understand the molecular mechanisms and the genetic control involved in genome rearrangements, we studied the evolution of the transcriptome during Paramecium tetraurelia sexual reproduction. RNA samples were extracted at different time points of mass cultures undergoing autogamy on normal food bacteria and on bacteria producing dsRNA to induce ND7 silencing. ND7 is a non-essential gene involved in the regulated discharge of trichocysts; the loss of function of this gene by with dsRNA feeding results in a mutant phenotype: non-discharge of trichocysts (Skouri and Cohen 1997).