Ultrastructural cytochemistry as a tool for studying transcriptional mechanisms

Ultrastructural cytochemistry is a powerful tool for investigating the biology of the cell nucleus. Thanks to its very high resolution, it has been possible to localize with extreme accuracy the sites of transcription, splicing and maturation of both mRNA and rRNA, their precise location as well as their movements. By means of immunocytochemical techniques, many nuclear proteins have been given a specific role in the transcriptional mechanisms, with the possibility of precisely mapping their location on a single RNA fibril. Starting from the 70s, the techniques have evolved from the resolution of autoradiography to that of gold-coupled antibodies, reaching a resolution of few nanometers. The use of correlative microscopy techniques as well as of electron tomography has also allowed the 3D imaging of ribonucleoprotein-containing structures in situ, in the nucleus. The association of a biological mechanism with the cytochemical localization of a specific molecule has been crucial in defining the functional organization of the cell nucleus, and has been invaluable for the understanding of many biological processes.