Biomedical subjects

Trent P Munro

Publications and source records attributed to Trent P Munro.

6 recordsLinked to original sources

PubMed2006

A repeated IMP-binding motif controls oskar mRNA translation and anchoring independently of Drosophila melanogaster IMP.

Zip code-binding protein 1 (ZBP-1) and its Xenopus laevis homologue, Vg1 RNA and endoplasmic reticulum-associated protein (VERA)/Vg1 RNA-binding protein (RBP), bind repeated motifs in the 3' untranslated regions (UTRs) of localized mRNAs. Although these motifs are required for RNA localization, the necessity of ZBP-1/VERA remains unresolved. We address the role of ZBP-1/VERA through analysis of the Drosophila melanogaster homologue insulin growth factor II mRNA-binding protein (IMP). Using systematic evolution of ligands by exponential enrichment, we identified the IMP-binding element (IBE) UUUAY, a motif that occurs 13 times in the oskar 3'UTR. IMP colocalizes with oskar mRNA at the oocyte posterior, and this depends on the IBEs. Furthermore, mutation of all, or subsets of, the IBEs prevents oskar mRNA translation and anchoring at the posterior. However, oocytes lacking IMP localize and translate oskar mRNA normally, illustrating that one cannot necessarily infer the function of an RBP from mutations in its binding sites. Thus, the translational activation of oskar mRNA must depend on the binding of another factor to the IBEs, and IMP may serve a different purpose, such as masking IBEs in RNAs where they occur by chance. Our findings establish a parallel requirement for IBEs in the regulation of localized maternal mRNAs in D. melanogaster and X. laevis.

3' Untranslated Regions↗

PubMed2004

The Drosophila hnRNPA/B homolog, Hrp48, is specifically required for a distinct step in osk mRNA localization.

The Staufen-dependent localization of oskar mRNA to the posterior of the Drosophila oocyte induces the formation of the pole plasm, which contains the abdominal and germline determinants. In a germline clone screen for mutations that disrupt the posterior localization of GFP-Staufen, we isolated three missense alleles in the hnRNPA/B homolog, Hrp48. These mutants specifically abolish osk mRNA localization, without affecting its translational control or splicing, or the localization of bicoid and gurken mRNAs and the organization of the microtubule cytoskeleton. Hrp48 colocalizes with osk mRNA throughout oogenesis, and interacts with its 5' and 3' regulatory regions, suggesting that it binds directly to oskar mRNA to mediate its posterior transport. The hrp48 alleles cause a different oskar mRNA localization defect from other mutants, and disrupt the formation of GFP-Staufen particles. This suggests a new step in the localization pathway, which may correspond to the assembly of Staufen/oskar mRNA transport particles.

3' Untranslated Regions↗

PubMed2003

A molecular mechanism for mRNA trafficking in neuronal dendrites.

Specific neuronal mRNAs are localized in dendrites, often concentrated in dendritic spines and spine synapses, where they are translated. The molecular mechanism of localization is mostly unknown. Here we have explored the roles of A2 response element (A2RE), a cis-acting signal for oligodendrocyte RNA trafficking, and its cognate trans-acting factor, heterogeneous nuclear ribonucleoprotein (hnRNP) A2, in neurons. Fluorescently labeled chimeric RNAs containing A2RE were microinjected into hippocampal neurons, and RNA transport followed using confocal laser scanning microscopy. These RNA molecules, but not RNA lacking the A2RE sequence, were transported in granules to the distal neurites. hnRNP A2 protein was implicated as the cognate trans-acting factor: it was colocalized with RNA in cytoplasmic granules, and RNA trafficking in neurites was compromised by A2RE mutations that abrogate hnRNP A2 binding. Coinjection of antibodies to hnRNP A2 halved the number of trafficking cells, and treatment of neurons with antisense oligonucleotides also disrupted A2RE-RNA transport. Colchicine inhibited trafficking, whereas cells treated with cytochalasin were unaffected, implicating involvement of microtubules rather than microfilaments. A2RE-like sequences are found in a subset of dendritically localized mRNAs, which, together with these results, suggests that a molecular mechanism based on this cis-acting sequence may contribute to dendritic RNA localization.

Animals↗

PubMed2002

RNA trafficking and stabilization elements associate with multiple brain proteins.

Two of the best understood somatic cell mRNA cytoplasmic trafficking elements are those governing localization of beta-actin and myelin basic protein mRNAs. These cis-acting elements bind the trans-acting factors fibroblast ZBP-1 and hnRNP A2, respectively. It is not known whether these elements fulfil other roles in mRNA metabolism. To address this question we have used Edman sequencing and western blotting to identify six rat brain proteins that bind the beta-actin element (zipcode). All are known RNA-binding proteins and differ from ZBP-1. Comparison with proteins that bind the hnRNP A2 and AU-rich response elements, A2RE/A2RE11 and AURE, showed that AURE and zipcode bind a similar set of proteins that does not overlap with those that bind A2RE11. The zipcode-binding protein, KSRP, and hnRNP A2 were selected for further study and were shown by confocal immunofluorescence microscopy to have similar distributions in the central nervous system, but they were found in largely separate locations in cell nuclei. In the cytoplasm of cultured oligodendrocytes they were segregated into separate populations of cytoplasmic granules. We conclude that not only may there be families of trans-acting factors for the same cis-acting element, which are presumably required at different stages of mRNA processing and metabolism, but independent factors may also target different and multiple RNAs in the same cell.

Actins↗

PubMed2002

UUCAC- and vera-dependent localization of VegT RNA in Xenopus oocytes.

Localized mRNAs are directed to their destinations by "localization elements" (LEs) in their 3'UTRs. LEs harbor multiple, functionally redundant localization "signals." These signals are poorly defined, hence it is unclear whether the signals-and their cognate factors-are unique to each RNA or employed generally. Five "E2s" (UUCACs) in the 366 nt Vg1 LE (VgLE) direct this transcript to the vegetal pole of Xenopus oocytes via the binding of a protein-Vera/Vg1RBP/ZBP. Here we show that a different vegetal RNA, VegT, employs the same signal and factor. Five E2s within a 440 nt subregion (VegT440) of the VegT 3'UTR predict its LE and are both necessary and sufficient (in the context of antisense VegT440) for directing localization. The E2s in VegT440 and VgLE function similarly to recruit Vera protein: (1) in both contexts, E2 nt substitutions partially (UU to AC) or completely (CA to UG) inhibit localization in accordance with the sequence selectivity of Vera protein for E2s; (2) VegT440 and VgLE crosscompete, in an E2-dependent manner, for localization and Vera binding; (3) injection of anti-Vera antibody into oocytes inhibits localization of both injected transcripts. These findings imply that general localization signals traffic diverse RNAs.

3' Untranslated Regions↗

PubMed2002

Heterogeneous nuclear ribonucleoprotein A3, a novel RNA trafficking response element-binding protein.

The cis-acting response element, A2RE, which is sufficient for cytoplasmic mRNA trafficking in oligodendrocytes, binds a small group of rat brain proteins. Predominant among these is heterogeneous nuclear ribonucleoprotein (hnRNP) A2, a trans-acting factor for cytoplasmic trafficking of RNAs bearing A2RE-like sequences. We have now identified the other A2RE-binding proteins as hnRNP A1/A1(B), hnRNP B1, and four isoforms of hnRNP A3. The rat and human hnRNP A3 cDNAs have been sequenced, revealing the existence of alternatively spliced mRNAs. In Western blotting, 38-, 39-, 41-, and 41.5-kDa components were all recognized by antibodies against a peptide in the glycine-rich region of hnRNP A3, but only the 41- and 41.5-kDa bands bound antibodies to a 15-residue N-terminal peptide encoded by an alternatively spliced part of exon 1. The identities of these four proteins were verified by Edman sequencing and mass spectral analysis of tryptic fragments generated from electrophoretically separated bands. Sequence-specific binding of bacterially expressed hnRNP A3 to A2RE has been demonstrated by biosensor and UV cross-linking electrophoretic mobility shift assays. Mutational analysis and confocal microscopy data support the hypothesis that the hnRNP A3 isoforms have a role in cytoplasmic trafficking of RNA.

Aged↗