A novel fluorescent probe for the localization of nucleoli developed via a chain reaction of endogenous cysteine in cells.

Nucleolus imaging is important for the understanding of gene expression, proliferation, and growth of cells. Traditional nucleoli localization mainly relies on the use of RNA fluorescent probes which are required in large amounts. These probes also have low selectivity, thus causing the generated images to have high background noise and the localization of nucleoli to become vague. In the present paper, a novel probe for nucleoli localization, BEB-A, which can specifically bind to RNA via the chain reaction of endogenous cysteine (Cys), was designed and developed. In addition to its mitochondria-targeting ability, the BEB-A probe could be used in the imaging of Cys in the cytoplasm, and its product, BEB-OH, could quickly penetrate into the cell nucleus to combine with nucleolar RNA to generate strong red fluorescence signals. The luminescence property and RNA-binding capability of the probe were also investigated via theoretical calculations and molecular docking simulations. This work presents a tool that can be applied to analyze the variation of Cys in mitochondria and RNA in cells.