RNA imaging: seeing is believing

Twenty years ago, in the middle 1990s, a pending debate in the RNA cell biology field concerned the nuclear organization of pre-mRNA splicing. Localization studies using antibodies to detect proteins of the spliceosome and oligonucleotide probes that hybridized with the spliceosomal small nuclear RNAs had revealed that practically all building blocks of the splicing machinery were not uniformly distributed in the nucleus but rather appeared concentrated in defined regions. These regions were termed “nuclear speckles” or “splicing domains” due to the local enrichment in splicing factors. Whether or not pre-mRNA splicing occurred within these domains remained controversial. To address this question, it was critical to visualize the transition from nascent unspliced transcripts to the spliced forms. This was made possible through successive optimizations of in situ hybridization, a microscopic technique pioneered independently by Gall and Jones back in the late 1960s. An important advance was made by Lawrence, who introduced …