Meiotic silencing by unpaired DNA: properties, regulation and suppression.
In Neurospora, a gene not paired with a homolog in prophase I of meiosis generates a signal that transiently silences all sequences homologous to it by a process called meiotic silencing by unpaired DNA (MSUD). Thus a deletion mutation in a heterozygous cross is formally "ascus-dominant" because its unpaired wild-type partner silences itself. We describe in detail the isolation of a mutation, Sad-1(UV), that suppresses the dominance of various ascus-dominant mutations. Additional dominant, semidominant, and recessive Sad-1 alleles have been generated by RIP; the DNA of the dominant RIP alleles becomes methylated, but dim-2-dependent methylation is not necessary for silencing. The barrenness of homozygous Sad-1 crosses is not due to the failure to silence unpaired mating-type mat A-2 mat A-3 genes. Transcripts of sad-1(+) can be detected during the sexual phase in a homozygous wild-type cross, indicating that the gene is expressed even if all DNA can pair normally. Meiotic silencing is confined to the ascus in which DNA is unpaired, and silencing does not spread to neighboring asci in a fruiting body of mixed genetic constitution.
Shiu
Patrick K T
PK
Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA.
Metzenberg
Robert L
RL
D000595:Amino Acid Sequence; D001483:Base Sequence; D015966:Gene Expression Regulation, Fungal; D020868:Gene Silencing; D018398:Homeodomain Proteins / Q000235:genetics; D008540:Meiosis; D008969:Molecular Sequence Data; D009491:Neurospora / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics
D018398:Homeodomain Proteins; D012097:Repressor Proteins; C093512:SAD1 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins