Development of the fluorescent probe CenSpark for labeling centrioles and cilia.

Small-molecule probes are transformative for cell biology, offering unprecedented insights into subcellular structures, including in systems without molecular genetic tools. Centrioles are fundamental for generating the axoneme of cilia and flagella, as well as centrosomes, but a generic small-molecule probe allowing selective visualization of centriolar and axonemal microtubules is lacking. We engineered CenSpark as a cell-permeable dual-ligand fluorescent probe exploiting the juxtaposition of inner and outer microtubule-binding sites of microtubule triplets and doublets present exclusively in centriolar and axonemal microtubules. This design endows CenSpark high selectivity in live and fixed specimen analysis of centrioles, cilia and flagella across systems. We deployed CenSpark to uncover the rate of primary cilium formation and track centrioles in chimeric antigen receptor T cells during polarization at the immunological synapse with unprecedented resolution. Overall, CenSpark is a novel versatile small-molecule fluorescent probe to monitor centrioles, cilia and flagella without the need for genetic manipulation.