Protein subcellular localization is fundamental to the establishment of the body axis, cell migration, synaptic plasticity, and a vast range of other biological processes. Protein localization occurs through three mechanisms: protein transport, mRNA localization, and local translation. However, the relative contribution of each process to neuronal polarity remains unknown. Using neurons differentiated from mouse embryonic stem cells, we analyze protein and RNA expression and translation rates in isolated cell bodies and neurites genome-wide. We quantify 7323 proteins and the entire transcriptome, and identify hundreds of neurite-localized proteins and locally translated mRNAs. Our results demonstrate that mRNA localization is the primary mechanism for protein localization in neurites that may account for half of the neurite-localized proteome. Moreover, we identify multiple neurite-targeted non-coding RNAs and RNA-binding proteins with potential regulatory roles. These results provide further insight into the mechanisms underlying the establishment of neuronal polarity.

GENETICS: D. BRUCK that various mono-or polyvalent alcohols interfere with these excitations, while other substances, like sugars, promote them. It seems probable that dimerizations are involved in these phenomena, as described by Scheibe,2 Rabinowitch and Epstein,3 and others. If so, the excitations could be symbolized by the following equations: A+ B-AB, hp + AB OA**B-bA*B*, or hp +AB *A*B*, A and B standing for the two dimerizing molecules and the asterisk for their excitation. Why dimerization facilities transition into the triple state has to be decided by further studies.

The assignment of specific ribosomal functions to individual ribosomal proteins is difficult due to the enormous cooperativity of the ribosome; however, important roles for distinct ribosomal proteins are becoming evident. Although ribosomal ribonucleic acid (rRNA) has the major claim to certain aspects of ribosome function, such as decoding and peptidyltransferase activity, there are also protein‐dominated functional hot‐spots on the ribosome such as the messenger RNA (mRNA) entry pore, the translation factor‐binding site and the exit of the ribosomal tunnel. The latter is binding site for both chaperones and complexes associated with protein transport through membranes. Furthermore, the contribution of ribosomal proteins is essential for the assembly and optimal functioning of the ribosome. Key Concepts A universal nomenclature for the ribosomal proteins was introduced in 2014, which terminates the babylonic chaos of the various nomenclature systems. About two thirds of the bacterial ribosomal proteins have counterparts in archaeal and eukaryotic ribosomes. Both rRNA and ribosomal proteins are essential for assembly, structure and function of the ribosomes. A few ribosomal proteins are essential for the assembly, but lack a function in the mature ribosome. In addition to rRNA‐dominated functional hot‐spots such as the decoding centre and the peptidyl‐transferase centre, there are also protein‐dominated functional hot‐spots such as the entry pore for the mRNA on the 30S subunit, the docking site for G‐protein factors and the exit of the tunnel harbouring the nascent peptide chain.

Our current knowledge about the mechanisms of miRNA silencing is restricted to few lineages such as vertebrates, arthropods, nematodes and land plants. miRNA-mediated silencing in bilaterian animals is dependent on the proteins of the GW182 family. Here, we dissect the function of GW182 protein in the cnidarian Nematostella, separated by 600 million years from other Metazoa. Using cultured human cells, we show that Nematostella GW182 recruits the CCR4-NOT deadenylation complexes via its tryptophan-containing motifs, thereby inhibiting translation and promoting mRNA decay. Further, similarly to bilaterians, GW182 in Nematostella is recruited to the miRNA repression complex via interaction with Argonaute proteins, and functions downstream to repress mRNA. Thus, our work suggests that this mechanism of miRNA-mediated silencing was already active in the last common ancestor of Cnidaria and Bilateria.

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