Properties of unpaired DNA required for efficient silencing in Neurospora crassa.
The presence of unpaired copies of a gene during meiosis triggers silencing of all copies of the gene in the diploid ascus cell of Neurospora. This phenomenon is called meiotic silencing and on the basis of genetic studies appears to be a post-transcriptional gene silencing (PTGS) mechanism. Previously, meiotic silencing was defined to be induced by the presence of a DNA region lacking an identical segment in the homologous chromosome. However, the determinants of unpaired DNA remained a mystery. Using the Ascospore maturation-1 (Asm-1) gene, we defined what needs to be "unpaired" to silence a gene. For efficient silencing, an unpaired region of DNA needs to be of a sufficient size and contain homology to the reporter transcript. The greater the size of the loop and the larger the homology to the reporter transcript, the better the resulting meiotic silencing is. Conversely, regions not containing homology to the transcript, e.g., intergenic regions, did not silence the reporter. Surprisingly, unpaired fragments lacking a canonical promoter silenced the reporter. Additionally, we detected the unpairing-dependent loss of a transcript during meiotic silencing. Our observations further support a PTGS mechanism for meiotic silencing and offer insight into the evolutionary consequences resulting from this novel meiotic checkpoint.
Lee
Dong W
DW
Department of Biology, College of Science, Texas A&M University, College Station, Texas 77843-3258, USA.
Seong
Kye-Yong
KY
Pratt
Robert J
RJ
Baker
Kevin
K
Aramayo
Rodolfo
R
D000483:Alleles; D003433:Crosses, Genetic; D004247:DNA / Q000235:genetics* / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000235:genetics*; D017353:Gene Deletion; D020868:Gene Silencing; D017930:Genes, Reporter; D008040:Genetic Linkage; D005838:Genotype; D006639:Histidine / Q000737:chemistry; D008540:Meiosis; D008957:Models, Genetic; D009492:Neurospora crassa / Q000235:genetics*; D010957:Plasmids / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
C104110:ASM-1 protein, Neurospora crassa; D018076:DNA, Complementary; D005656:Fungal Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D006639:Histidine; D012313:RNA; D004247:DNA