DNA-based fluorescent probes of NOS2 activity in live brains

Proc Natl Acad Sci U S A. 2020 Jun 30;117(26):14694-14702. doi: 10.1073/pnas.2003034117. Epub 2020 Jun 17.


Innate immune cells destroy pathogens within a transient organelle called the phagosome. When pathogen-associated molecular patterns (PAMPs) displayed on the pathogen are recognized by Toll-like receptors (TLRs) on the host cell, it activates inducible nitric oxide synthase (NOS2) which instantly fills the phagosome with nitric oxide (NO) to clear the pathogen. Selected pathogens avoid activating NOS2 by concealing key PAMPs from their cognate TLRs. Thus, the ability to map NOS2 activity triggered by PAMPs can reveal critical mechanisms underlying pathogen susceptibility. Here, we describe DNA-based probes that ratiometrically report phagosomal and endosomal NO, and can be molecularly programmed to display precise stoichiometries of any desired PAMP. By mapping phagosomal NO produced in microglia of live zebrafish brains, we found that single-stranded RNA of bacterial origin acts as a PAMP and activates NOS2 by engaging TLR-7. This technology can be applied to study PAMP-TLR interactions in diverse organisms.

Keywords: live imaging; microglia; nitric oxide; nitric oxide synthase-2 (NOS2); phagosome.

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

  • Animals
  • Brain / enzymology*
  • Brain / metabolism
  • Brain Chemistry
  • DNA / chemistry*
  • DNA / metabolism
  • Fluorescent Dyes / chemistry*
  • Fluorescent Dyes / metabolism
  • Gene Knockout Techniques
  • Mice
  • Microglia / chemistry
  • Microglia / enzymology
  • Microglia / metabolism
  • Microscopy, Fluorescence
  • Molecular Probes / chemistry
  • Molecular Probes / metabolism
  • Nitric Oxide Synthase Type II* / analysis
  • Nitric Oxide Synthase Type II* / chemistry
  • Nitric Oxide Synthase Type II* / metabolism
  • Phagosomes / chemistry
  • Phagosomes / metabolism
  • Zebrafish


  • Fluorescent Dyes
  • Molecular Probes
  • DNA
  • Nitric Oxide Synthase Type II