Methods for visualizing RNA processing and transport pathways in living cells

Recent advances in fluorescence microscopy, imaging, and probe technology provided possibilities to study the spatial and temporal distribution of RNA species in living cells. While some methods: have been developed to localize all nascent or poly (A) containing transcripts others have been developed to study the in vivo distribution of specific RNA species. Irrespective of the method that has been used, the results of these studies provided important information concerning the localization and the cellular transport pathways of RNAs. Also, the picture emerges that RNA molecules travel through the nucleus at much faster speed, equaling that of free diffusion, than previously anticipated. Still, a major challenge proves to be the development of a microscopic detection technique that allows specific, in vivo, detection of low levels of RNA species by fluorescence in situ hybridization, without interfering fluorescent background signals derived from non-hybridized probe sequences and autofluorescent cell components. By applying photoactivatable caged fluorochrome-, molecular beacon-, or fluorescence resonance energy transfer (FRET)-based detection methods an important step in the future of living cell analysis has already been made.