It has generally been assumed that all neuronal RNA granules have essentially similar compositions. However, the new findings indicate that this is not the case. A comparison between Stau2- and Barentsz-containing granules reveals that they differ in about two-thirds of their proteins. "This suggests that the RNA granules are highly heterogeneous and dynamic in their composition," says Kiebler. "And that makes sense to me, because it would mean that the granules can perform different functions depending on which mRNAs they carry." Furthermore, the researchers have shown that the granules contain virtually none of the factors known to promote the translation of mRNAs into proteins. On the contrary, they include many molecules that repress protein synthesis. This in turn implies that the process of mRNA transport is uncoupled from the subsequent production of the proteins they encode.
In a complementary study, Kiebler's team also characterized the mRNA cargoes associated with the granules. "Until now, none of the RNA molecules present in Stau2-containing granules in mammalian nerve cells had been defined, but we have now been able to identify many specific mRNAs," Kiebler explains. Further experiments revealed that Stau2 stabilizes the mRNAs, allowing them to be used more often for the production of proteins. Moreover, the researchers have shown that specialized structures within these mRNAs, called "Staufen-Recognized Structures" (SRS), are essential for their recognition and stabilization by Stau2. "This
|Contact: Luise Dirscherl|