Addendum to: Nature Communications https://doi.org/10.1038/s41467-017-00698-y, published online 21 September 2017

We would like to make our readers aware of the publication by Alvarez-Castelao et al., which reports the original development of the Floxed MetRS L274G mice for the cell-specific labelling of proteins in vivo and provides an in-depth characterisation of these mice1. Breeding pairs of Floxed mice were graciously donated by Erin Schuman and coworkers well in advance of the publication by Alvarez-Castelao et al. Application of this technology to cell transplantation, selective identification of ‘young’ proteins in the setting of heterochronic parabiosis, and array proteomics was developed by the Conboy laboratory.