The RPD3L deacetylation complex is required for facultative heterochromatin repression in Neurospora crassa

Area of Science:

• Epigenetics
• Molecular Biology
• Developmental Biology

Background:

• Facultative heterochromatin repression is vital for development across many species.
• Histone H3 lysine 27 (H3K27) methylation by Polycomb repressive complex 2 marks facultative heterochromatin.
• The precise mechanism of H3K27-mediated gene silencing remains unclear.

Purpose of the Study:

• To identify genes essential for maintaining facultative heterochromatin silencing in Neurospora crassa.
• To elucidate the role of novel genes in the H3K27 methylation-dependent gene repression pathway.

Main Methods:

• Employed a forward genetics approach in Neurospora crassa to screen for genes affecting heterochromatin silencing.
• Utilized molecular techniques to identify and characterize novel silencing genes: sds3, rlp1, and rlp2.
• Investigated the association of identified proteins with known epigenetic complexes and analyzed histone modification patterns.

Main Results:

• Identified three new genes (sds3, rlp1, rlp2) critical for facultative heterochromatin silencing.
• Found that SDS3, RLP1, and RLP2 associate with Neurospora homologs of the Rpd3L complex.
• Demonstrated that these genes are required for repressing a subset of H3K27-methylated genes without affecting H3K27 methylation levels.
• Observed increased histone H3 lysine 14 acetylation at upregulated genes upon deletion of these factors, indicating a role for deacetylation in silencing.

Conclusions:

• SDS3, RLP1, and RLP2, components of the Rpd3L complex, are essential for facultative heterochromatin gene silencing in Neurospora crassa.
• RPD3L-mediated deacetylation, specifically at histone H3 lysine 14, appears to be a key mechanism for silencing H3K27-methylated genes.
• These findings suggest a conserved role for RPD3L in facultative heterochromatin regulation across eukaryotes.