Life at Low Copy Number: How Dendrites Manage with So Few mRNAs.

Most mammalian dendrites have surprisingly few copy numbers of mRNAs relative to the large number of synapses and consequently, at any given moment, the majority of synapses do not have a repertoire of mRNAs within their immediate locale capable of initiating translation-dependent plasticity. The dimensions of the translationally serviceable locale around synapses have boundary parameters that can be estimated. When a synapse receives an input beyond that boundary, the requisite mRNAs for local translation and plasticity may not be there. How a complex dendritic arbor optimizes this paucity of mRNAs opens several functional considerations that are related to the dynamic range of dendritic plasticity, sparse coding, and modifications of firing rates. RNA localization in dendrites may instantiate a neuron's history and establishes a bias toward inputs that synapse on RNA-laden synaptic clusters. Low copy numbers create an element of stochasticity to the induction of translation-dependent plasticity that allows the dendrite opportunities to respond to novel and unexpected inputs.