mRNA on the Move: The Road to Its Biological Destiny

Abstract

Cells have evolved to regulate the asymmetric distribution of specific mRNA targets to institute spatial and temporal control over gene expression. Over the last few decades, evidence has mounted as to the importance of localization elements in the mRNA sequence and their respective RNA-binding proteins. Live imaging methodologies have shown mechanistic details of this phenomenon. In this minireview, we focus on the advanced biochemical and cell imaging techniques used to tweeze out the finer aspects of mechanisms of mRNA movement.mRNA transport and cytoplasmic compartmentalization of protein synthesis allow precise control over spatial and temporal gene expression and are essential for survival and response to extracellular cues. It has been shown that mRNA localization is essential for cell fate determination (1), directed cell movement (2), and tissue functionality (3). About 3 decades ago, it was discovered that mRNA was asymmetrically distributed in eggs and embryos (4) and in oocytes (5-7) and that this localization was necessary to convey proper embryonic patterning during development. Concurrently, it was found that mRNA could also localize in differentiated somatic cells such as migrating fibroblasts (8), oligodendrocytes (9), and neurons (Table 1) (10). It is now understood that the localization of specific mRNA targets, facilitated by RNA-binding proteins (RBPs), 3 is a highly conserved mechanism to spatially restrict protein production, amplify local protein concentration, or even direct integration into macromolecular complexes, sometimes co-translationally (reviewed in . RBPs are multifunctional regulators, as they are responsible for processing, localizing, and controlling the translation of a host of mRNA targets. Sometimes, a unique RBP can carry an mRNA from the nucleus to its final destination in a translationally repressed state. Local cues altering its association with the mRNA may ensure compartmentalized translation (15,16). Many RBPs that govern mRNA localization are preferentially expressed during critical developmental stages, where differentiation, survival, or cell migration is necessary to establish tissue patterning (3). Modifying the expression of trans-acting RBPs (i.e. knockdown/out or overexpression) or mutating cis-acting regulatory elements present in mRNA targets leads to developmental or cognitive deficiencies (17, 18) and a host of disease states (19). Advances in new imaging technologies have allowed the visualization and quantitation of mRNA localization in fixed and living cells, facilitating a more detailed analysis of the molecular mechanisms involved in the process.In this minireview, we discuss the current knowledge of mRNA movement from its birth to its final destination within the eukaryotic cell and the impact that biochemical approaches complemented by single molecule imaging techniques have made on the field. How Does mRNA Localize?mRNA localization is directed by cis-acting localization elements (LEs), also known as zipcodes, typically present in the 3Ј-UTR of ...

Novel RNA-binding Protein P311 Binds Eukaryotic Translation Initiation Factor 3 Subunit b (eIF3b) to Promote Translation of Transforming Growth Factor β1-3 (TGF-β1-3)

“…In co-IP mass spectrometry studies, P311 also showed an association with several cytoskeletal proteins, including filamin, previously reported to interact with P311 (44), myosin heavy chain, and ␤-actin, suggesting that, besides the stimulation of translation of TGF-␤1-3, another P311 function may be to link TGF-␤ transcripts to molecular motors for active transport (45). The previously observed binding of P311 to the TGF-␤1 latent associated protein by two-yeast hybridization and co-IP (46) was not seen in this study.…”

De novo translation initiation on membrane-bound ribosomes as a mechanism for localization of cytosolic protein mRNAs to the endoplasmic reticulum

“…Prominently studied examples of mRNA localization, notably embryonic polarity determination in the Drosophila embryo, directed cell migration, and neurite morphogenesis, have revealed a common mechanism where cis-encoded localization information (zip codes), cognate RNA binding proteins, and molecular motors direct translationally silenced mRNAs to specific subcellular locales (Martin and Ephrussi 2009;Eliscovich et al 2013). In addition to these cell-specific mRNA localization phenomena, all eukaryotic cells localize signal peptide-encoding mRNAs to the endoplasmic reticulum (ER) by a distinct, translationdependent mechanism, the signal recognition particle (SRP) pathway (Lingappa and Blobel 1980;Walter and Johnson 1994;Akopian et al 2013).…”

Labelling and imaging of single endogenous messenger RNA particlesin vivo

“…The best-studied RNA is probably the β-actin mRNA (Eliscovich et al, 2013). It can be targeted to specific subcellular compartments by a zipcode protein and undergo directed transport to reach its destination (Lifland et al, 2011).…”

“…1). Traditionally, cells stably expressing the MBS sequence at the RNA of interest were transfected with MCP-fluorescent-protein, which enabled studies of intranuclear processing and transport, nuclear export and cytosolic transport of single mRNPs (reviewed in Eliscovich et al, 2013). Recently, a transgenic mouse carrying both the MBS and green fluorescent protein (GFP)-tagged MCP sequences was created, allowing the observation of β-actin mRNA at endogenous levels within live mouse tissue (Park et al, 2014).…”

“…The first successful labelling and imaging of single mRNPs in vivo was achieved about 10 years ago (Fusco et al, 2003). Since then, labelling techniques, optical microscopy, tracking procedures and analysis tools have evolved dramatically (for review, see Weil et al, 2010;Eliscovich et al, 2013;Pitchiaya et al, 2014). Combinations of dedicated imaging technology and in vivo labelling have enabled studies of nuclear export (Grünwald and Singer, 2010;Siebrasse et al, 2012;Ma et al, 2013), and observation of the threedimensional (3D) trajectories of single RNA particles within living eukaryotic cells (Spille et al, 2015;Smith et al, 2015).…”