The advantage of periodic over constant signalling in microRNA-mediated repression
Cells have been found out to exploit oscillatory rather than constant gene expression to encode biological information. Temporal features of oscillations such as pulse frequency and amplitude have been shown determinant for the outcome of signaling pathways. However, little effort has been devoted to unveiling the role of pulsatility in the context of post-transcriptional gene regulation, where microRNAs (miRNAs) - repressors of gene expression - act by binding to RNAs. Here we study the effects of periodic against constant miRNA synthesis. We model periodic pulses of miRNA synthesis in a minimal miRNA-target RNA network by ODEs, and we compare the RNA repression to that resulting from constant synthesis of the repressor. We find that a pulsatile synthesis can induce more effective target RNA repression in the same timespan, despite an identical amount of repressor. In particular, a stronger fold repression is induced if the miRNA is synthesized at optimal frequencies, thereby showing a frequency preference behaviour - also known as "band-pass filtering". Moreover, we show that the preference for specific input frequencies is determined by relative miRNA and target kinetic rates, thereby highlighting a potential mechanism of selective target regulation. Such ability to differentially regulate distinct targets might represent a functional advantage in post-transcriptional repression, where multiple competing targets are regulated by the same miRNA. Thereby analyzing a model with two RNA target species, we show how competition influences the frequency-dependent RNA repression. Eventually, we find that periodic miRNA expression can lead to exclusive frequency-dependent repression on distinct RNA species, and we show how this depends on their relative kinetics of interaction with the repressor. Our findings might have implications for experimental studies aimed at understanding how periodic patterns drive biological responses through miRNA-mediated signalling, and provide suggestions for validation in a synthetic miRNA-target network.