MicroRNAs (miRNAs) are short 19-25 nucleotide RNA molecules that impact on most biological
processes by regulating the efficiency of messenger RNA (mRNA) translation. To date, most research
activities have been focused on the control of miRNA expression and its functional consequences.
Nonetheless, much remains unknown about the mechanisms affecting the level of specific
miRNAs in the cell, a critical feature impacting their regulatory activity. This review focuses on the factors
that regulate the abundance of miRNAs, including synthesis, post-transcriptional modifications, nucleases,
target binding, and secretion.