MicroRNAs—Versatile Regulators of Gene Networks

miRNAs and Plasticity
miRNAs function not only in a constitutive manner, maintaining lifelong cellular identity, but also in a short-term manner at the level of the synapses. To affect long-term changes at the synapses, local translation at the synapses is needed. “Synapses have nearly all of the translational machinery of cells,” said Dr. Kosik. “That allows two synapses on the same neuron to be controlled quite differently.”

Using in situ hybridization, Dr. Kosik’s group confirmed the presence of miRNA in dendrites and determined their copy numbers. Neurons have about 103 to 104 miRNAs per cell. Dr. Kosik speculated that the numbers of miRNAs may approximate the numbers of synapses. This implies either that a single synapse contains very small numbers of miRNAs or they are very unevenly distributed.

“If the numbers of [miRNAs] and synapses are very small and therefore take on stochastic properties, whether or not a synapse will go on to exhibit the translational changes needed for short-term memory has a random facet to it,” concluded Dr. Kosik.