NATF (Native And Tissue-Specific Fluorescence): A Strategy for Bright, Tissue-Specific GFP Labeling of Native Proteins in .

GFP labeling by genome editing can reveal the authentic location of a native protein but is frequently hampered by weak GFP signals and broad expression across a range cell types in multicellular animals. To overcome these problems, we engineered a Native And Tissue-specific Fluorescence (NATF) strategy which combines CRISPR/Cas-9 and split-GFP to yield bright, cell-specific protein labeling. We use CRISPR/Cas9 to insert a tandem array of seven copies of the GFP11 beta-strand (gfp11x7) at the genomic locus of each target protein. The resultant gfp11x7 knock-in strain is then crossed with separate reporter lines that express the complementing split-GFP fragment (gfp1-10) in specific cell types thus affording tissue-specific labeling of the target protein at its native level. We show that NATF reveals the otherwise undetectable intracellular location of the immunoglobulin protein, OIG-1, and demarcates a receptor auxiliary protein LEV-10 at cell-specific synaptic domains in the C. elegans nervous system.