Table 3.

Actin-detecting probes.

Probe	Description	Mechanisms	Pitfalls
Actin-chromobody [259]	A DNA plasmid encoding an anti-actin VHH nanobody fused to a fluorescent protein.	Fluorescent-labeled nanobody labels endogenous actin by antigen-antibody reaction.	High background when transient transfected into cells. Signal quenching after cell fixation.
Actin-GFP [260]	A DNA plasmid encoding human actin fused to GFP.	Ectopic expression of fluorescent-labeled actin into cells.	Interfere with the physiological actin dynamics.
F-tractin [261]	A DNA plasmid encoding N-terminus 10–52 AA peptides of rat inositol-trisphosphate 3-kinase (Itpk) [262].	Itpk has a F-actin specifically binding domain at the N-terminus 1–66 AA region [263].	Inhibit ABPs binding to F-actin.
Lifeact [264]	A DNA plasmid encoding N-terminus 1–17 AA peptides of yeast ABP140 [265].	Lifeact binds to G-actin with an affinity 10-fold higher than F-actin.	Alter F-actin organization [266].
Phalloidin [267]	Bicyclic heptapeptide from death cap mushroom.	Phalloidin specifically binds at the interface between subunits of F-actin, locking the F-actin structure and preventing depolymerization.	Prevent F-actin depolymerization. Cytotoxicity.
SiR-actin [268]	Silicon-rhodamine (SiR) conjugated to desbromo-desmethyl-jasplakinolide.	SiR is a fluorophore [269]. Jasplakinolide binds at the interface of G-actin oligomers at the nucleation phase [270, 271].	Enhance F-actin polymerization. Cytotoxicity.
SPY-actin	Improved version of the SiR-actin by utilizing SPY dyes instead of SiR.
UtrCH [272]	A DNA plasmid encoding N-terminus 1–261 AA peptides of human utrophin.	The N-terminus of utrophin has calponin-homology (CH) domains, which specifically binds to F-actin [273].	Alter F-actin organization.