The eukaryotic nucleus is compartmentalised into a number of functional domains, including chromosome territories and nuclear bodies. The Cajal body is one of the most prominent nuclear bodies and is thought to be the site for formation of small nuclear and small nucleolar ribonucleoprotein particles (snRNPs and snoRNPs, respectively). Although it is known that Cajal bodies contain a number of proteins, such as coilin, fibrillarin, dyskerin and Nopp140, in addition to snRNPs and snoRNPs, the mechanism underlying their formation remained unclear so far. Here, Hideaka Takata, Kei-ichi Shibahara and colleagues (p. ) shed light on the biogenesis of these snRNA-related suborganelles by highlighting a role for the integrator complex in establishing Cajal bodies. They show that RNAi-mediated depletion of two integrator subunits (INTS4 and INTS11) results in the relocalisation of coilin to the nucleolus instead of to Cajal bodies. In addition, the Cajal body component survival of motor neuron protein (SMN) and Sm proteins localise to the cytoplasm, where they form prominent cytoplasmic granules. The authors also find that cells lacking INTS4 accumulate premature U2 snRNAs in the nucleus and conclude that the 3′-end processing activity of snRNAs by the integrator complex is crucial for the formation of completely functional Cajal bodies.
