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Updated: May 13, 2026
Meiotic Spindle Assessment in Mouse Oocytes by siRNA-mediated Silencing
Published on: October 11, 2015
Novel proteins required for meiotic silencing by unpaired DNA and siRNA generation in Neurospora crassa
Thomas M Hammond1, Hua Xiao, Erin C Boone
1School of Biological Sciences, Illinois State University, Normal, Illinois 61790, USA. tmhammo@ilstu.edu
Abstract:
During meiosis in the filamentous fungus Neurospora crassa, unpaired genes are identified and silenced by a process known as meiotic silencing by unpaired DNA (MSUD). Previous work has uncovered six proteins required for MSUD, all of which are also essential for meiotic progression. Additionally, they all localize in the perinuclear region, suggesting that it is a center of MSUD activity. Nevertheless, at least a subset of MSUD proteins must be present inside the nucleus, as unpaired DNA recognition undoubtedly takes place there. In this study, we identified and characterized two new proteins required for MSUD, namely SAD-4 and SAD-5. Both are previously uncharacterized proteins specific to Ascomycetes, with SAD-4 having a range that spans several fungal classes and SAD-5 seemingly restricted to a single order. Both genes appear to be predominantly expressed in the sexual phase, as molecular study combined with analysis of publicly available mRNA-seq datasets failed to detect significant expression of them in the vegetative tissue. SAD-4, like all known MSUD proteins, localizes in the perinuclear region of the meiotic cell. SAD-5, on the other hand, is found in the nucleus (as the first of its kind). Both proteins are unique compared to previously identified MSUD proteins in that neither is required for sexual sporulation. This homozygous-fertile phenotype uncouples MSUD from sexual development and allows us to demonstrate that both SAD-4 and SAD-5 are important for the production of masiRNAs, which are the small RNA molecules associated with meiotic silencing.
Insights
Researchers identified two new proteins, SAD-4 and SAD-5, crucial for meiotic silencing by unpaired DNA (MSUD) in Neurospora crassa. These proteins are vital for producing small RNAs that mediate this silencing process during sexual reproduction.
Area of Science:
- Genetics
- Molecular Biology
- Fungal Biology
Background:
- Meiotic silencing by unpaired DNA (MSUD) is a process in Neurospora crassa where unpaired genes during meiosis are silenced.
- Six proteins essential for MSUD and meiotic progression have been identified, primarily localized to the perinuclear region.
- The precise nuclear localization of some MSUD proteins is inferred due to the nuclear site of unpaired DNA recognition.
Purpose of the Study:
- To identify and characterize novel proteins involved in MSUD.
- To investigate the localization and function of these new proteins in relation to MSUD and sexual development.
- To determine the role of these proteins in the production of MSUD-associated small RNAs.
Main Methods:
- Gene identification and characterization of SAD-4 and SAD-5 in Neurospora crassa.
- Analysis of gene expression using molecular studies and mRNA-seq datasets.
- Subcellular localization studies of SAD-4 and SAD-5 during meiosis.
- Phenotypic analysis of mutants for MSUD and sexual sporulation defects.
- Assessment of small interfering RNA production in mutant strains.
Main Results:
- Two new MSUD proteins, SAD-4 and SAD-5, were identified, specific to Ascomycetes.
- SAD-4 localizes to the perinuclear region, while SAD-5 is the first MSUD protein found within the nucleus.
- Unlike previously known MSUD proteins, SAD-4 and SAD-5 are not required for sexual sporulation, indicating a dissociation of MSUD from sexual development.
- SAD-4 and SAD-5 are essential for the production of meiotic small interfering RNAs (masiRNAs) linked to MSUD.
Conclusions:
- SAD-4 and SAD-5 are newly discovered, essential components of the MSUD pathway in Neurospora crassa.
- The distinct localization of SAD-5 within the nucleus highlights a more complex spatial regulation of MSUD than previously understood.
- The identification of MSUD proteins dispensable for sexual sporulation provides a tool to dissect MSUD independently of meiotic progression.
- These findings establish SAD-4 and SAD-5 as key regulators of masiRNA biogenesis, critical for effective meiotic silencing by unpaired DNA.
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