Involvement of FMRP in Primary MicroRNA Processing via Enhancing Drosha Translation

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Fragile X mental retardation protein (FMRP) regulates gene expression post-transcriptionally in the brain.
• FMRP is implicated in microRNA (miRNA) biogenesis, converting precursor miRNAs (pre-miRNAs) to mature miRNAs.
• The specific role of FMRP in primary miRNA (pri-miRNA) processing remained unclear.

Purpose of the Study:

• To investigate the novel role of FMRP in pri-miRNA processing.
• To elucidate the mechanism by which FMRP influences pri-miRNA processing, focusing on Drosha.
• To understand the implications of FMRP's function in fragile X syndrome.

Main Methods:

• Analyzing DROSHA protein and mRNA levels in Fmr1-knockout mice hippocampus and FMRP-knockdown Neuro-2a cells.
• Assessing Drosha mRNA stability following FMRP manipulation.
• Employing immunoprecipitation and polysome analysis to detect FMRP binding to Drosha mRNA and its translational effect.
• Quantifying pri-miRNA, pre-miRNA, and mature miRNA levels in Fmr1-deficient mice.

Main Results:

• DROSHA protein, not its mRNA, was downregulated in FMRP-deficient models.
• FMRP binds to Drosha mRNA and enhances its translation, independent of mRNA stability.
• Loss of FMRP led to pri-miRNA accumulation and reduced pre-miRNA and mature miRNA levels.
• Specifically, three out of six analyzed pri-miRNAs were affected.

Conclusions:

• FMRP plays a novel role in pri-miRNA processing by enhancing DROSHA protein expression via translational control.
• This mechanism highlights FMRP's involvement in miRNA biogenesis and its potential significance in fragile X syndrome.
• FMRP's regulation of Drosha is a key pathway impacting miRNA maturation and gene expression in the brain.