Detection of unpaired DNA at meiosis results in RNA-mediated silencing

During meiosis, homologous chromosomes must pair in order to permit recombination and correct chromosome segregation to occur. Two recent papers(1,2) show that meiotic pairing is also important for correct gene expres-sion during meiosis. They describe data for the filamen-tous fungus Neurospora crassa that show that a lack of pairing generated by ectopic integration of genes can result in silencing of genes expressed during meiosis. This can result in aberrant meioses whose defects are specific to the function of the unpaired gene. Further-more, mutations affecting the silencing mechanism have been selected in a gene encoding a putative RNA-dependent RNA polymerase. This finding indicates the involvement of a meiotic specific post-transcriptional gene silencing mechanism (PTGS) similar to that ob-served in vegetative cells in N. crassa and other organ-isms. Finally, this gene product is essential for normal meiosis, suggesting that RNA-dependent processes are fundamental to the sexual cycle. BioEssays 25:99–103