Most polyribosomes are found in spines during LTP (bottom dendrite).
Harris/Elsevier
The first article, by Linnaea Ostroff, Kristen Harris, and colleagues (Boston University, Boston, MA), demonstrates that polyribosomes get redistributed to dendritic spines during long-term potentiation (LTP). LTP enhances synaptic responses and is currently thought to promote forms of learning and memory. Although the first phase of LTP is translation independent, sustained LTP is known to require new protein synthesis.
Harris's results indicate that the newly made proteins may not have to travel far. Using Star Wars–quality three-dimensional reconstructions of serial sections of neuronal tissue, the authors showed that synapse-containing dendritic protrusions known as spines accumulated polyribosomes when given an LTP-inducing stimulus. This gain was accompanied by a loss of polyribosomes in the nearby main body of the dendrite.
Larger synapses were found on the spines that had gained polyribosomes, indicating that increased local protein synthesis enhances synaptic activity. “The next phase is unraveling which proteins are synthesized there,” says Harris. Candidates include scaffolding proteins, which could stabilize the synapse-enhancing glutamate receptors inserted into the plasma membrane during the translation-independent phase of LTP.
In the second paper, axons were also shown to have translation ability. Perry Brittis, Qiang Lu, and John Flanagan (Harvard Medical School, Boston, MA) isolated axons and growth cones and found these were able not only to translate RNAs that they were fed, but also to transport the newly synthesized proteins to the cell surface. Their results also showed that axons were capable of localized translational up-regulation of receptor mRNAs, possibly to change responsiveness to guidance cues during pathfinding. ▪
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