Dosage and temporal thresholds in microRNA proteomics.

Area of Science:

• Molecular Biology
• Genetics
• Bioinformatics

Background:

• MicroRNAs (miRNAs) are key regulators of gene expression, impacting protein and mRNA levels via translational repression and mRNA decay.
• Understanding miRNA target interactions is crucial for deciphering gene regulatory networks.

Purpose of the Study:

• To identify primary miRNA targets using integrated proteomics and RNAseq.
• To compare the stringency and accuracy of different miRNA target prediction algorithms.
• To investigate variations in miRNA repression kinetics, concentration sensitivity, and underlying mechanisms.

Main Methods:

• Combined SILAC-based proteomics and RNAseq for quantitative measurements of protein and mRNA repression.
• Analyzed transcript 3'UTR sequences for miRNA binding sites.
• Evaluated miRNA target prediction algorithms (Targetscan, PITA, miRanda).
• Assessed the correlation between repression thresholds and thermodynamic parameters (ΔΔG, ΔGopen).

Main Results:

• Identified primary miRNA targets with higher stringency using Targetscan and PITA compared to miRanda.
• Observed significant variations in repression kinetics and sensitivity to exogenous miRNA concentration.
• Detected bimodal repression thresholds (low vs. high miRNA concentration; early vs. late time points).
• Correlated repression thresholds with the net free energy of miRNA-target interactions, influenced by 3'UTR secondary structures near binding sites.
• Found biphasic repression responses in a subset of proteins.

Conclusions:

• MiRNA target repression exhibits varying modes, leading to diverse response thresholds in kinetics and concentration.
• Target site accessibility, influenced by RNA structures and protein binding, plays a critical role in modulating miRNA efficacy.
• Cellular conditions affecting steady-state miRNA levels can lead to graded responses in target gene sensitivity and fold-change.