Separable roles for Microprocessor and its cofactors ERH and SAFB1/2 during microRNA cluster assistance

Area of Science:

• Molecular Biology
• RNA Biology
• Gene Regulation

Background:

• MicroRNAs (miRNAs) are crucial small RNAs regulating gene expression.
• Some miRNA loci have suboptimal features requiring regulatory mechanisms for efficient biogenesis.
• Cluster assistance, where an optimal miRNA neighbor aids a suboptimal one, is a known but poorly understood process.

Purpose of the Study:

• To elucidate the mechanisms underlying miRNA cluster assistance.
• To identify critical interactions between the Microprocessor complex and its cofactors in this process.
• To define the roles of ERH and SAFB factors in miRNA cluster assistance.

Main Methods:

• Utilized mutant cells of Microprocessor complex and cofactors (Drosha, DGCR8, ERH, SAFB1/2).
• Analyzed miRNA structure-function variants and employed biochemical assays.
• Performed genomewide profiling and epistatic tests to order cofactor functions.

Main Results:

• Defined features of suboptimal miRNAs dependent on cluster assistance.
• Identified a subset of Microprocessor-cofactor interactions critical for cluster assistance.
• Established a pathway where ERH mediates Microprocessor transfer and SAFB factors (SAFB2) mediate recognition and binding of suboptimal miRNA hairpins.
• Demonstrated cluster assistance integrates into a feedback loop via Drosha cleavage of DGCR8 transcript.

Conclusions:

• MiRNA cluster assistance involves complex regulatory transactions for efficient biogenesis of clustered miRNAs.
• ERH and SAFB factors play distinct, ordered roles in facilitating Microprocessor complex function for suboptimal miRNAs.
• A feedback loop involving Drosha cleavage of DGCR8 regulates the Microprocessor complex, integrating cluster assistance into broader regulatory networks.