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Additional file 1: Supplementary figures. Fig. S1. Protein-to-mRNA ratios detect differences in translational efficiency among tissues. Fig. S2. Differences in secretion, protein half-life and mRNA half-life among tissues. Fig. S3. Random Forest models identify two clusters of human tissues with distinct codon signatures. Fig. S4. Random Forest models of HPA and GTEx datasets independently. Fig. S5. Random Forest models of tissue-specific mRNA and protein levels. Fig. S6. Differences between tissues are also observed at the codon pair level. Fig. S7. CUSTOM generates fluorescent variants with desired tissue-specific expression. Fig. S8. Proteomics and RT-qPCR of CUSTOM-optimized constructs.

Additional file 8. Peer review history.

Wnt proteins are secreted hydrophobic glycoproteins that act over long distances through poorly understood mechanisms. We discovered that Wnt7a is secreted on extracellular vesicles (EVs) following muscle injury. Structural analysis identified the motif responsible for Wnt7a secretion on EVs that we term the Exosome Binding Peptide (EBP). Addition of the EBP to an unrelated protein directed secretion on EVs. Disruption of palmitoylation, knockdown of WLS, or deletion of the N-terminal signal peptide did not affect Wnt7a secretion on purified EVs. Bio-ID analysis identified Coatomer proteins as candidates responsible for loading Wnt7a onto EVs. The crystal structure of EBP bound to the COPB2 coatomer subunit, the binding thermodynamics, and mutagenesis experiments, together demonstrate that a dilysine motif in the EBP mediates binding to COPB2. Other Wnts contain functionally analogous structural motifs. Mutation of the EBP results in a significant impairment in the ability of Wnt7a to stimulate regeneration, indicating that secretion of Wnt7a on exosomes is critical for normal regeneration in vivo . Our studies have defined the structural mechanism that mediates binding of Wnt7a to exosomes and elucidated the singularity of long-range Wnt signalling.