Multicellular organisms are composed of tissues that have distinct functions requiring specialized proteomes. To define the proteome of a live animal with tissue and subcellular resolution, we adapted a localized proteomics technology for use in the multicellular model organism Caenorhabditis elegans. This approach couples tissue- and location-specific expression of the enzyme ascorbate peroxidase (APX), which enables proximity-based protein labeling in vivo, and quantitative proteomics to identify tissue- and subcellular-restricted proteomes. We identified and localized more than 3000 proteins from strains of C. elegans expressing APX in either the nucleus or cytoplasm of the intestine, epidermis, body wall muscle, or pharyngeal muscle. We also identified several hundred proteins that were specifically localized to one of the four tissues analyzed or specifically localized to the cytoplasm or the nucleus. This approach resulted in the identification both of proteins with previously characterized localizations and of those not known to localize to the nucleus or cytoplasm. Further, we confirmed the tissue- and subcellular-specific localization of a subset of identified proteins using green fluorescent protein tagging and fluorescence microscopy, validating our in vivo proximity-based proteomics technique. Together, these results demonstrate a new approach that enables the tissue- and subcellular-specific identification and quantification of proteins within a live animal.
Keywords: C. elegans; chemical biology; mass spectrometry; protein localization; spatially restricted enzymatic tagging; tissue-specific expression.