Novel regulation and functional interaction of polycistronic miRNAs

Area of Science:

• Molecular Biology
• Genetics
• Developmental Biology

Background:

• MicroRNAs (miRNAs) are crucial regulators of gene expression implicated in various diseases.
• Many miRNA genes are organized into polycistronic clusters, leading to coexpression.
• The mir-11∼998 cluster contains two miRNAs: miR-11 and miR-998.

Purpose of the Study:

• To investigate the regulatory mechanisms governing the processing and expression of miRNAs within polycistronic clusters.
• To elucidate the specific role of the mir-11 gene in the expression of miR-998.
• To understand the functional consequences of dysregulated miRNA expression within a cluster.

Main Methods:

• Investigated the requirement of miR-11 for Drosha-mediated processing of the pri-miRNA precursor.
• Utilized gene deletion and replacement strategies to assess the impact on miR-998 expression.
• Performed in vivo and in vitro experiments to validate findings.
• Examined developmental phenotypes resulting from altered miR-998 expression.

Main Results:

• The presence of miR-11 within the pri-miRNA is indispensable for its processing by Drosha.
• Deletion of the mir-11 gene completely abolished miR-998 expression.
• Replacing mir-11 with an unrelated miRNA or expressing miR-998 from a different scaffold restored its expression.
• Uncontrolled miR-998 expression in the absence of miR-11 led to significant developmental abnormalities.

Conclusions:

• A novel layer of cis-regulation exists within miRNA clusters, where one miRNA (miR-11) controls the processing and expression of another (miR-998).
• This regulatory mechanism ensures balanced miRNA function within clusters, preventing detrimental effects from unchecked expression.
• The findings suggest that such embedded regulation is a general principle in miRNA clusters, impacting multiple miRNA targets and biological responses.