DCL-1 colocalizes with other components of the MSUD machinery and is required for silencing

In Neurospora, a gene present in an abnormal number of copies is usually a red flag for mischief. One way to deal with these potential intruders is by destroying their transcripts. Widely known as RNA interference (RNAi), this mechanism depends on the dicing of a double-stranded RNA intermediate into small-interfering RNA, which in turn guide the degradation of mRNA from the target gene. Quelling is a vegetative silencing system in Neurospora that utilizes such a mechanism. Quelling depends on the redundant activity of two Dicer-like ribonucleases, DCL-1 and DCL-2. Here, we show that Meiotic Silencing by Unpaired DNA (MSUD), a mechanism that silences expression from unpaired DNA during meiosis, requires the dcl-1 (but not the dcl-2) gene for its function. This result suggests that MSUD operates in a similar manner to Quelling and other RNAi systems. DCL-1 colocalizes with SAD-1 (an RdRP), SAD-2, and SMS-2 (an Argonaute) in the perinuclear region. (c) 2007 Elsevier Inc. All rights reserved.