The presence of an unpaired copy of a gene during meiosis triggers the
silencing of every copy of that gene in the diploid ascus cell of Neurospora
crassa, a phenomenon called Meiotic Silencing. This phenomenon has two
stages: trans-sensing and meiotic silencing. If a DNA region is not detected on
the opposite homologous chromosome early in meiosis (a trans-sensing failure),
a signal corresponding to the unpaired region is produced that transiently
silences expression of all homologous sequences. Meiotic silencing is related to
RNA Silencing, a phenomenon that employs RNA-dependent RNA Polymerases
(RdRPs), Argonautes, and Dicers. Dicers cleave double-stranded RNA (dsRNA)
into 21-23 nucleotide RNAs. In the filamentous fungus Neurospora crassa, two
RNA silencing pathways have been identified; one is active during mitosis, and
the other is active during meiosis. The mitotic RNA silencing pathway, known as
“quelling”, involves an RdRP (quelling-deficient-1--qde-1), an Argonaute-like
protein (quelling-deficient-2--qde-2), and two Dicer-like proteins (dicer-like-1--dcl-1 and dicer-like-2--dcl-2). Previous studies in N. crassa also revealed the
involvement of an RdRP (Suppressor of ascus dominance-1--Sad-1) and an
Argonaute-like protein (Suppressor of meiotic silencing-2--Sms-2) in meiotic
silencing, suggesting that meiotic silencing is RNA-dependent and raising the
question of whether a Dicer is involved in meiotic silencing.
In this work, we tested the participation in meiotic silencing of the dcl-1 gene of
N. crassa, which codes for a Dicer-like protein we call Suppressor of meiotic
silencing-3--Sms-3. Crosses homozygous for mutant alleles of Sms-3 are
barren, indicating that the gene is also essential for sexual development. Due to
this homozygous sterility, we could only test the involvement of Sms-3 in meiotic
silencing in heterozygous crosses. Under these conditions, we observed
suppression of the meiotic silencing which would have otherwise been induced
by the presence of unpaired DNA of reporter genes. We conclude that the Dicerlike
protein Sms-3 is required for both meiotic RNA silencing and sexual
development.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2437 |
| Date | 15 May 2009 |
| Creators | McLaughlin, Malcolm Thomas |
| Contributors | Aramayo, Rodolfo |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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