Mitochondria contain the genetic information and expression machinery to produce essential respiratory chain proteins. Within the mitochondrial matrix, newly synthesized RNA, RNA processing proteins and mitoribosome assembly factors form punctate sub-compartments referred to as mitochondrial RNA granules (MRGs). Despite their proposed importance in regulating gene expression, the structural and dynamic properties of MRGs remain largely unknown. EPFL biophysicist Suliana Manley’team and Jean-Claude Martinou’s group investigated the internal architecture of MRGs and found that the MRG ultrastructure consists of compacted RNA embedded within a protein cloud. They revealed that MRGs rapidly exchange components and can undergo fusion, characteristic properties of fluid condensates. Furthermore, MRGs associate with the inner mitochondrial membrane and their fusion coincides with mitochondrial remodelling. Together, these findings reveal that MRGs are nanoscale fluid compartments, which are dispersed along mitochondria via membrane dynamics.
This study was published in Nature Cell Biology on September 28th 2020.