mRNA transport in fungal top models

Abstract

Eukaryotic cells rely on the precise determination of when and where proteins are synthesized. Spatiotemporal expression is supported by localization of mRNAs to specific subcellular sites and their subsequent local translation. This holds true for somatic cells as well as for oocytes and embryos. Most commonly, mRNA localization is achieved by active transport of the molecules along the actin or microtubule cytoskeleton. Key factors are molecular motors, adaptors, and RNA-binding proteins that recognize defined sequences or structures in cargo mRNAs. A deep understanding of this process has been gained from research on fungal model systems such as Saccharomyces cerevisiae and Ustilago maydis. Recent highlights of these studies are the following: (1) synergistic binding of two RNA-binding proteins is needed for high affinity recognition; (2) RNA sequences undergo profound structural rearrangements upon recognition; (3) mRNA transport is tightly linked to membrane trafficking; (4) mRNAs and ribosomes are transported on the cytoplasmic surface of endosomes; and (5) heteromeric protein complexes are, most likely, assembled co-translationally during endosomal transport. Thus, the study of simple fungal model organisms provides valuable insights into fundamental mechanisms of mRNA transport boosting the understanding of similar events in higher eukaryotes.

The multi PAM 2 protein Upa2 functions as novel core component of endosomal mRNA transport

“…Membrane-associated RBPs (memRBPs) are most likely important at all intracellular membranes to orchestrate spatiotemporal expression [37]. These findings stress the vital role of U. maydis as a model for RNA biology [4,10].…”

Core components of endosomal mRNA transport are evolutionarily conserved in fungi

“…Key factors are RNA-binding proteins (RBPs) that recognize cargo mRNAs and interact with accessory RBPs to form larger ribonucleoprotein complexes (mRNPs). These are linked to molecular motors (Niessing et al, 2018).…”

Selective sets of mRNAs localize to extracellular paramural bodies in a rice glup6 mutant

“…The mislocalization of storage-protein RNAs mediated by defective Rab5a ( Doroshenk et al , 2010 ), Rab5a-GEF, and Got1B ( Fukuda et al , 2016 ) and the transport of mRNAs to the extracellular PMBs is consistent with RNA localization co-opting membrane trafficking events. While a close association between these processes has been suggested in metazoans ( Gerst, 2008 ), substantial evidence for membrane-mediated RNA transport has been obtained in fungi and budding yeast cells ( Schmid et al , 2006 ; Kraut-Cohen and Gerst, 2010 ; Hermesh and Jansen, 2013 ; Haag et al , 2015 ; Niessing et al , 2018 ). In budding yeast, a subset of RNAs is co-transported with ER tubule membranes to the cortical region of the incipient daughter cells during the early phase of the cell cycle ( Aronov et al , 2007 ; Fundakowski et al , 2012 ).…”