Analysis of Spliceosomal snRNA Localization in Human Hela Cells Using Microinjection

Biogenesis of spliceosomal snRNAs is a complex process involving both nuclear and cytoplasmic phases and the last step occurs in a nuclear compartment called the Cajal body. However, sequences that direct snRNA localization into this subnuclear structure have not been known until recently. To determine sequences important for accumulation of snRNAs in Cajal bodies, we employed microinjection of fluorescently labelled snRNAs followed by their localization inside cells. First, we prepared snRNA deletion mutants, synthesized DNA templates for in vitro transcription and transcribed snRNAs in the presence of UTP coupled with Alexa488. Labelled snRNAs were mixed with 70 kDa-Dextran conjugated with TRITC, and microinjected to the nucleus or the cytoplasm of human HeLa cells. Cells were incubated for 1 h and fixed and the Cajal body marker coilin was visualized by indirect immunofluorescence, while snRNAs and dextran, which serves as a marker of nuclear or cytoplasmic injection, were observed directly using a fluorescence microscope. This method allows for efficient and rapid testing of how various sequences influence RNA localization inside cells. Here, we show the importance of the Sm-binding sequence for efficient localization of snRNAs into the Cajal body.