Bright split red fluorescent proteins for the visualization of endogenous proteins and synapses

Commun Biol. 2019 Sep 17:2:344. doi: 10.1038/s42003-019-0589-x. eCollection 2019.


Self-associating split fluorescent proteins (FPs) are split FPs whose two fragments spontaneously associate to form a functional FP. They have been widely used for labeling proteins, scaffolding protein assembly and detecting cell-cell contacts. Recently developments have expanded the palette of self-associating split FPs beyond the original split GFP1-10/11. However, these new ones have suffered from suboptimal fluorescence signal after complementation. Here, by investigating the complementation process, we have demonstrated two approaches to improve split FPs: assistance through SpyTag/SpyCatcher interaction and directed evolution. The latter has yielded two split sfCherry3 variants with substantially enhanced overall brightness, facilitating the tagging of endogenous proteins by gene editing. Based on sfCherry3, we have further developed a new red-colored trans-synaptic marker called Neuroligin-1 sfCherry3 Linker Across Synaptic Partners (NLG-1 CLASP) for multiplexed visualization of neuronal synapses in living C. elegans, demonstrating its broad applications.

Keywords: Fluorescence imaging; Fluorescent proteins; Genetic engineering; Neural circuits.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Fluorescent Dyes
  • Gene Expression*
  • Genes, Reporter*
  • HEK293 Cells
  • Humans
  • Luminescent Proteins / chemistry
  • Luminescent Proteins / genetics*
  • Luminescent Proteins / metabolism*
  • Microscopy, Fluorescence
  • Models, Molecular
  • Molecular Imaging
  • Red Fluorescent Protein
  • Structure-Activity Relationship
  • Synapses / metabolism*


  • Fluorescent Dyes
  • Luminescent Proteins