Interestingly, the cell-to-cell consistency of our single-cell measurements suggests precise regulation of miR-9 levels in neurons. One siRNA molecule with miRNA-like features can degrade several target molecules in a very short time (Hutvagner and Zamore, 2002). Thus, the cell needs to tightly control levels of miRNA, because even subtle changes in miRNA expression could have profound effects on the expression of miRNA targets. This could also explain why we observe such a massive downregulation of BK mRNA in a very short period of time, with relatively small (two- fold) upregulation of miR-9.
