Advertisement

Participation of Xenopus Elr-type Proteins in Vegetal mRNA Localization during Oogenesis*

  • Patrick K. Arthur
    Footnotes
    Affiliations
    Department of Developmental Biochemistry, Göttingen Center for Molecular Biosciences, University of Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
    Search for articles by this author
  • Maike Claussen
    Footnotes
    Affiliations
    Department of Developmental Biochemistry, Göttingen Center for Molecular Biosciences, University of Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
    Search for articles by this author
  • Susanne Koch
    Affiliations
    Department of Developmental Biochemistry, Göttingen Center for Molecular Biosciences, University of Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
    Search for articles by this author
  • Katsiaryna Tarbashevich
    Affiliations
    Department of Developmental Biochemistry, Göttingen Center for Molecular Biosciences, University of Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
    Search for articles by this author
  • Olaf Jahn
    Affiliations
    Proteomics Group, Max-Planck-Institute of Experimental Medicine, Hermann-Rein-Strasse 3, 37075 Göttingen, Germany
    Search for articles by this author
  • Tomas Pieler
    Correspondence
    To whom correspondence should be addressed. Tel.: 49-551-395683; Fax: 49-551-3914614
    Affiliations
    Department of Developmental Biochemistry, Göttingen Center for Molecular Biosciences, University of Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
    Search for articles by this author
  • Author Footnotes
    * This work was supported by funds from the Deutsche Forsch ungs ge mein schaft Grant SFB523 (to T. P.) and by the research program of the Faculty of Medicine, Georg-August-University Göttingen (to M. C.).
    The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1–S7 and Tables S1 and S2.
    1 These authors contributed equally to this work.
Open AccessPublished:May 20, 2009DOI:https://doi.org/10.1074/jbc.M109.009928
      Directional transport of specific mRNAs is of primary biological relevance. In Xenopus oocytes, mRNA localization to the vegetal pole is important for germ layer formation and germ cell development. Using a biochemical approach, we identified Xenopus Elr-type proteins, homologs of the Hu/ELAV proteins, as novel components of the vegetal mRNA localization machinery. They bind specifically to the localization elements of several different vegetally localizing Xenopus mRNAs, and they are part of one RNP together with other localization proteins, such as Vg1RBP and XStaufen 1. Blocking Elr-type protein binding by either localization element mutagenesis or antisense morpholino oligonucleotide-mediated masking of their target RNA structures, as well as overexpression of wild type and mutant ElrB proteins, interferes with vegetal localization in Xenopus oocytes.
      mRNA localization to the vegetal pole of Xenopus oocytes establishes a primary axis of asymmetry that is crucial for early embryonic development. Two major transport pathways that guide specific mRNAs to the vegetal cortex can be distinguished from each other. The early or METRO pathway operates via the mitochondrial cloud during earliest stages of oogenesis. Several early localizing mRNAs have been found to be involved in germ cell development (
      • Zhou Y.
      • King M.L.
      ). Although early localizing RNAs like Xcat2 or Xdazl become first enriched in the mitochondrial cloud by a microtubule-independent diffusion/entrapment mechanism and relocate to the vegetal cortex during stage II along with components of the fragmented mitochondrial cloud (
      • Forristall C.
      • Pondel M.
      • Chen L.
      • King M.L.
      ,
      • Kloc M.
      • Etkin L.D.
      ,
      • Mosquera L.
      • Forristall C.
      • Zhou Y.
      • King M.L.
      ,
      • Chang P.
      • Torres J.
      • Lewis R.A.
      • Mowry K.L.
      • Houliston E.
      • King M.L.
      ), late pathway RNAs like Vg1, VegT, and Velo1 are initially homogenously dispersed throughout the cytoplasm (
      • Kloc M.
      • Etkin L.D.
      ,
      • Rebagliati M.R.
      • Weeks D.L.
      • Harvey R.P.
      • Melton D.A.
      ,
      • Weeks D.L.
      • Melton D.A.
      ,
      • Lustig K.D.
      • Kroll K.L.
      • Sun E.E.
      • Kirschner M.W.
      ,
      • Stennard F.
      • Carnac G.
      • Gurdon J.B.
      ,
      • Zhang J.
      • King M.L.
      ,
      • Claussen M.
      • Pieler T.
      ). The late transport pathway is activated at mid-oogenesis (stages III and IV) and is mediated by a motor-driven, microtubule-dependent mechanism (
      • Betley J.N.
      • Heinrich B.
      • Vernos I.
      • Sardet C.
      • Prodon F.
      • Deshler J.O.
      ,
      • Messitt T.J.
      • Gagnon J.A.
      • Kreiling J.A.
      • Pratt C.A.
      • Yoon Y.J.
      • Mowry K.L.
      ,
      • Yisraeli J.K.
      • Sokol S.
      • Melton D.A.
      ,
      • Yoon Y.J.
      • Mowry K.L.
      ). Several of the late localizing mRNAs are critical for germ layer formation (
      • White J.A.
      • Heasman J.
      ). A small population of RNAs exhibits localization features of both pathways and is therefore referred to as intermediate pathway RNAs (
      • Chan A.P.
      • Kloc M.
      • Etkin L.D.
      ,
      • Pannese M.
      • Cagliani R.
      • Pardini C.L.
      • Boncinelli E.
      ,
      • Zearfoss N.R.
      • Chan A.P.
      • Wu C.F.
      • Kloc M.
      • Etkin L.D.
      ).
      Both early and late localization pathways are under the control of regulatory RNA elements, usually residing in the 3′-UTR
      The abbreviations used are: UTR
      untranslated region
      LE
      localization element
      PBS
      phosphate-buffered saline
      IP
      immunoprecipitation
      wt
      wild type
      RRM
      RNA recognition motif
      VTE
      Vg1 translational element.
      3The abbreviations used are: UTR
      untranslated region
      LE
      localization element
      PBS
      phosphate-buffered saline
      IP
      immunoprecipitation
      wt
      wild type
      RRM
      RNA recognition motif
      VTE
      Vg1 translational element.
      of localized mRNAs, referred to as localization elements (LEs) or mitochondrial cloud localization element (reviewed in Refs.
      • Jambhekar A.
      • Derisi J.L.
      and
      • King M.L.
      • Messitt T.J.
      • Mowry K.L.
      ). LEs recruit proteins to form a localization complex. Although proteins that exclusively interact with LEs from early localizing RNAs and that could mediate the entrapment in the MC have not been identified to date, a number of proteins that interact with the localization element of the late localizing Vg1 mRNA have been identified; they include Vg1RBP, hnRNP I, Prrp, VgRBP71/KSRP, XStaufen 1, and 40LoVe (
      • Yoon Y.J.
      • Mowry K.L.
      ,
      • Havin L.
      • Git A.
      • Elisha Z.
      • Oberman F.
      • Yaniv K.
      • Schwartz S.P.
      • Standart N.
      • Yisraeli J.K.
      ,
      • Deshler J.O.
      • Highett M.I.
      • Abramson T.
      • Schnapp B.J.
      ,
      • Cote C.A.
      • Gautreau D.
      • Denegre J.M.
      • Kress T.L.
      • Terry N.A.
      • Mowry K.L.
      ,
      • Zhao W.M.
      • Jiang C.
      • Kroll T.T.
      • Huber P.W.
      ,
      • Kroll T.T.
      • Zhao W.M.
      • Jiang C.
      • Huber P.W.
      ,
      • Czaplinski K.
      • Köcher T.
      • Schelder M.
      • Segref A.
      • Wilm M.
      • Mattaj I.W.
      ). Interestingly, mitochondrial cloud localization elements of all early pathway RNAs tested to date can enter the late localization pathway if injected into stage III/IV oocytes, suggesting that they are able to recruit late transport proteins (
      • Chan A.P.
      • Kloc M.
      • Etkin L.D.
      ,
      • Claussen M.
      • Horvay K.
      • Pieler T.
      ,
      • Hudson C.
      • Woodland H.R.
      ,
      • Allen L.
      • Kloc M.
      • Etkin L.D.
      ,
      • Zhou Y.
      • King M.L.
      ). This may serve as a fail-proof mechanism to ensure vegetal cortex localization of early pathway RNAs that are transcribed late, after mitochondrial cloud breakdown.
      A core transport RNP containing hnRNP I and Vg1RBP is formed in the nucleus and exported to the cytoplasm. Although Vg1RBP and hnRNP I form direct protein-protein interactions in the nucleus, complex formation becomes RNase-sensitive in the cytoplasm, suggesting that a remodeling step occurs after export to the cytoplasm (
      • Kress T.L.
      • Yoon Y.J.
      • Mowry K.L.
      ,
      • Lewis R.A.
      • Gagnon J.A.
      • Mowry K.L.
      ). VgRBP71/KSRP and 40LoVe can also be detected in the nucleus, but whether they are indeed part of a nuclear transport RNP remains to be determined (
      • Kroll T.T.
      • Zhao W.M.
      • Jiang C.
      • Huber P.W.
      ,
      • Czaplinski K.
      • Köcher T.
      • Schelder M.
      • Segref A.
      • Wilm M.
      • Mattaj I.W.
      ). The reassembly step in the cytoplasm includes the recruitment of additional proteins; whereas hnRNP I, Vg1RBP, Prrp, XStaufen 1, and 40LoVe accompany the localizing RNA in the vegetal cytoplasm and get enriched at the cortex (
      • Yoon Y.J.
      • Mowry K.L.
      ,
      • Zhao W.M.
      • Jiang C.
      • Kroll T.T.
      • Huber P.W.
      ,
      • Czaplinski K.
      • Köcher T.
      • Schelder M.
      • Segref A.
      • Wilm M.
      • Mattaj I.W.
      ,
      • Kress T.L.
      • Yoon Y.J.
      • Mowry K.L.
      ,
      • Allison R.
      • Czaplinski K.
      • Git A.
      • Adegbenro E.
      • Stennard F.
      • Houliston E.
      • Standart N.
      ,
      • Zhang Q.
      • Yaniv K.
      • Oberman F.
      • Wolke U.
      • Git A.
      • Fromer M.
      • Taylor W.L.
      • Meyer D.
      • Standart N.
      • Raz E.
      • Yisraeli J.K.
      ), VgRBP71/KSRP is found throughout the cytoplasm with a slight enrichment at the animal cortex (
      • Kroll T.T.
      • Zhao W.M.
      • Jiang C.
      • Huber P.W.
      ). Rather than directly participating in the vegetal transport, VgRBP71/KSRP has been suggested to translationally activate cortical Vg1 mRNA by stimulating a nuclease that cleaves off the Vg1 translational control element (TCE) (
      • Kolev N.G.
      • Huber P.W.
      ). Because of its interaction with profilin, a regulator of actin dynamics, Prrp has been proposed to function in the microfilament-dependent anchoring of localized RNA at the cortex (
      • Zhao W.M.
      • Jiang C.
      • Kroll T.T.
      • Huber P.W.
      ). The recruitment of Staufen 1 into the transport particle might be mediated by hnRNP I, because dominant negative Staufen 1 mutants not only affect vegetal localization of injected RNAs but also lose interaction with hnRNP I (
      • Yoon Y.J.
      • Mowry K.L.
      ).
      The active particle transport along microtubule filaments is mediated by overlapping functions of kinesin I and II plus-end directed motor proteins (
      • Betley J.N.
      • Heinrich B.
      • Vernos I.
      • Sardet C.
      • Prodon F.
      • Deshler J.O.
      ,
      • Messitt T.J.
      • Gagnon J.A.
      • Kreiling J.A.
      • Pratt C.A.
      • Yoon Y.J.
      • Mowry K.L.
      ,
      • Yoon Y.J.
      • Mowry K.L.
      ). Further remodeling of the localization RNP is likely to occur at the vegetal cortex, where late localizing RNAs become anchored. Cytokeratin intermediate filaments, in addition to microfilaments, seem to be required for anchoring (
      • Yisraeli J.K.
      • Sokol S.
      • Melton D.A.
      ,
      • Alarcón V.B.
      • Elinson R.P.
      ). Interestingly, vegetally localized RNAs themselves may function as structural components of the cortical cytokeratin meshwork, because antisense oligodeoxynucleotide-mediated depletion of localized RNAs like VegT or xlsirts disrupts the cytokeratin network and leads to a release of specific RNAs from the vegetal cortex (
      • Heasman J.
      • Wessely O.
      • Langland R.
      • Craig E.J.
      • Kessler D.S.
      ,
      • Kloc M.
      • Etkin L.D.
      ,
      • Kloc M.
      • Wilk K.
      • Vargas D.
      • Shirato Y.
      • Bilinski S.
      • Etkin L.D.
      ).
      Proteins of the ELAV/Hu protein family are RNA-binding proteins that contain three RRM domains, with RRM2 and 3 being separated by a linker region (
      • Good P.J.
      ). Vertebrates express four members of ELAV/Hu-type proteins, namely the ubiquitous HuR (also called HuA or ElrA in Xenopus), HuB (Hel-N1, ElrB), which is expressed in neurons, testes and ovaries, as well as the strictly neuronal proteins HuC (ElrC) and HuD (ElrD). ELAV/Hu-type proteins bind to AU-rich regions and function in a wide variety of posttranscriptional processes, such as control of RNA stability, translational regulation, splicing, and polyadenylation, as well as nucleocytoplasmic transport (reviewed in Ref.
      • Hinman M.N.
      • Lou H.
      ). As part of its role in translational regulation, HuR has recently been described to mediate the stress-induced release of microRNA-silenced RNAs from P-bodies for active translation (
      • Bhattacharyya S.N.
      • Habermacher R.
      • Martine U.
      • Closs E.I.
      • Filipowicz W.
      ). Xenopus ElrA/B proteins have been shown to interact with the translational control element of Vg1 mRNA (VTE) and anti-HuR antibody injections support a role for ElrB in the translational repression of Vg1 mRNA during early to mid-oogenesis (
      • Colegrove-Otero L.J.
      • Devaux A.
      • Standart N.
      ).
      We have previously characterized the function of the late localizing XDead end (XDE) mRNA in Xenopus. As revealed by UV cross-linking experiments, its localization element (XDE-LE) binds to a set of unknown proteins with molecular masses between 35 and 45 kDa (
      • Horvay K.
      • Claussen M.
      • Katzer M.
      • Landgrebe J.
      • Pieler T.
      ). Here, we report on the identification of these proteins as Xenopus ElrA/B proteins. We further show that Elr-type proteins are part of one RNP complex together with other localization proteins from Xenopus oocytes. ElrA/B bind to a number of additional LEs from both early and late localizing mRNAs. Interfering with Elr-LE interaction, as well as overexpression of wild type or mutant versions of ElrB, results in a loss of vegetal mRNA localization, arguing for a critical role of Elr-type proteins during vegetal RNA localization.

      DISCUSSION

      Data reported in this communication reveal that Xenopus Elr-type proteins, homologs of Hu/ELAV proteins, bind specifically to the XDead end-LE, as well as to a number of other Xenopus localization elements. ElrA/B proteins co-fractionate in an RNA-dependent manner along with known localization proteins such as Vg1RBP and XStaufen 1 on glycerol gradients, and co-precipitation analysis indicates that that they assemble into the same RNP. Interference with ElrA/B binding by either LE-mutagenesis or co-injection of antisense morpholino oligonucleotides, as well as results obtained from overexpression of wt or mutant versions of ElrB, provide strong evidence that ElrA/B binding is indeed crucial for the vegetal localization of the XDE-LE RNA. UV cross-linking as well as co-immunoprecipitation analysis indicates that ElrA/B proteins might also function in the localization of other vegetally localized RNAs. However, ElrA/B binding does not seem to reflect a general requirement for vegetal localization, because the LE of the late localizing RNA Xvelo1 does not exhibit binding activities for these proteins and is not affected by overexpression of dominant negative ElrB mutants. It thus seems possible that localizing RNAs might assemble into different localization RNPs, either containing or lacking ElrA/B proteins.
      It is of interest to define how exactly ElrA/B proteins function during vegetal RNA localization; because a small quantity of ElrA can be detected in the oocyte nuclei, it might assemble with the localization RNP already in the nucleus. Nucleocytoplasmic transport studies indicate that Xenopus ElrA is rapidly exported to the cytoplasm after nuclear injection, which is probably mediated by the conserved HNS (HuR nuclear shuttling sequence) that is located in the hinge region separating RRM2 and 3 and which has previously been shown to mediate nuclear shuttling of HuR (
      • Fan X.C.
      • Steitz J.A.
      ). Because ElrB, similar to the strictly neuronal Hu family members HuC and HuD, exhibits an insertion in the hinge region interfering with the HNS function, it seems likely that ElrB enters the localization RNP after export to the cytoplasm. Whether ElrA and B differ in respect to their functional role during vegetal transport remains to be determined. Co-immunoprecipitation data revealed an RNA-dependent interaction with Vg1RBP, 40LoVe, and XStaufen 1, indicating that ElrA/B are part of localization particles during their migration in the cytoplasm. Xenopus ElrB has been reported to oligomerize on its target RNAs (
      • Devaux A.
      • Colegrove-Otero L.J.
      • Standart N.
      ), suggesting that ElrB might function as an assembly factor for the formation of large RNA transport granules that may also contain multiple localized transcripts. Immunostaining for ElrA/B, XStaufen 1, and 40LoVe revealed co-localization in large particles in the vegetal cytoplasm, which may correspond to such transport granules. In addition, these transport granules might also mediate translational repression of the localizing RNA, either by sequestering the RNAs in silencing complexes that are not accessible for the translation machinery and/or by recruitment of translational repressors into the transport granule, as has been shown for the Bruno-mediated translational repression of oskar mRNA particles e.g. (
      • Chekulaeva M.
      • Hentze M.W.
      • Ephrussi A.
      ). Co-immunoprecipitation of the RNA-helicase Xp54 and Rap55-related Lsm domain proteins RAP42 and RAP46 along with ElrA/B indicates that ElrA/B containing localization RNPs might indeed be transported in a translationally repressed state. Xenopus Xp54 has been described as a component of stored mRNPs that also represses translation of reporter RNAs in the MS2-tethered function assay (
      • Ladomery M.
      • Wade E.
      • Sommerville J.
      ,
      • Minshall N.
      • Standart N.
      ), and the Drosophila Xp54 homolog Me31b has been shown to participate in translational repression of the posterior localizing RNA oskar (
      • Nakamura A.
      • Amikura R.
      • Hanyu K.
      • Kobayashi S.
      ). Similarly, the Lsm domain protein Rap55 has been reported to be part of translationally repressed mRNP complexes in Xenopus oocytes and acts a translational repressor in vitro as well as in oocytes if tethered to a reporter RNA (Ref.
      • Tanaka K.J.
      • Ogawa K.
      • Takagi M.
      • Imamoto N.
      • Matsumoto K.
      • Tsujimoto M.
      ; reviewed in Ref.
      • Marnef A.
      • Sommerville J.
      • Ladomery M.R.
      ). In addition to a role during the transport process, co-localization with XStaufen 1 and 40LoVe at the vegetal cortex suggests that ElrA/B might also function in anchoring the RNP complex after transport has been completed.
      Hu/ELAV RNA-binding proteins function in various aspects of RNA metabolism, including splicing and nuclear export, as well as regulation of mRNA stability and translation (reviewed in Refs.
      • Hinman M.N.
      • Lou H.
      ,
      • Brennan C.M.
      • Steitz J.A.
      , and
      • Gorospe M.
      ). Hu/ELAV proteins are known to specifically target localized RNAs in other systems, although no indications for a direct function of Hu/ELAV proteins in RNA localization have been described to date. In particular, HuR was reported to bind to the 3′-UTR of β-actin mRNA, which localizes to the leading edge of migrating cells, a process that also involves the Vg1RBP homolog ZBP1 (
      • Dormoy-Raclet V.
      • Ménard I.
      • Clair E.
      • Kurban G.
      • Mazroui R.
      • Di Marco S.
      • von Roretz C.
      • Pause A.
      • Gallouzi I.E.
      ,
      • Condeelis J.
      • Singer R.H.
      ). It was demonstrated that depletion of HuR results in a reduced migratory capacity of such cells, perhaps as a consequence of reduced β-actin mRNA stability (
      • Dormoy-Raclet V.
      • Ménard I.
      • Clair E.
      • Kurban G.
      • Mazroui R.
      • Di Marco S.
      • von Roretz C.
      • Pause A.
      • Gallouzi I.E.
      ). In neurons, the Vg1RBP homolog IMP1, together with HuD, is found to exert a repressing effect on the translation of Tau mRNA 3′-UTR reporters (
      • Atlas R.
      • Behar L.
      • Sapoznik S.
      • Ginzburg I.
      ). Tau 3′-UTR not only regulates translation but also contains the axonal localization signal that mediates mRNA localization to the axon in neuronal cells (
      • Aronov S.
      • Aranda G.
      • Behar L.
      • Ginzburg I.
      ). Although, in these cases, Hu/ELAV proteins are reported to control the stability and translation of localized RNAs, our study provides evidence for a direct function of Xenopus ElrA/B proteins during vegetal transport in oocytes.
      Binding of Elr-type proteins to the AU-rich translational control element in the 3′-UTR of the vegetally localizing mRNA Vg1 (VTE) was reported to exert a repressing effect on translation (
      • Colegrove-Otero L.J.
      • Devaux A.
      • Standart N.
      ). However, although we could reproduce the translational repressor function of the ElrA/B-binding VTE, we did not observe a strict correlation between ElrA/B binding activity and translational repression or transcript stability in the context of diverse vegetal localization elements,. In particular, luciferase reporter assays revealed that wild type XDE-LE compared with mut2, lacking ElrA/B-binding sites, did not mediate a repressive effect but rather a slight stimulation of translation (data not shown). Thus, it seems likely, that the diverse functions of Elr-type proteins in Xenopus and those of their homologs in other biological systems are context-dependent and are modulated by additional factors, such as Vg1RBP, hnRNP I, and XStaufen 1 in the process of RNA localization, and so-far unknown factors mediating the translational repression of VTE-containing RNAs. This dependence on co-factors could also explain why Xenopus ElrB protein alone is not able to mediate translational repression if tethered to a MS2 stem-loop containing luciferase reporter RNA by the viral MS2 coat protein.
      M. Claussen and T. Pieler, unpublished results.
      To unravel the diverse functions of Elr-type/Hu proteins in RNA metabolism in more detail, it will be of crucial future interest to define the composition and structural arrangement of the different functional RNPs that contain these proteins.

      Acknowledgments

      We thank J. Yisraeli for the α-Vg1RBP antibody, N. Standart for the α-XStaufen 1 antibody, K. Czaplinski and I. W. Mattaj for the α-40LoVe antibody, S. Hüttelmaier and N. Stöhr for help with the calculation of RNA enrichment factors, C. Viebahn and colleagues for cryosectioning of oocytes, and I. Eckhardt for excellent technical assistance.

      REFERENCES

        • Zhou Y.
        • King M.L.
        IUBMB Life. 2004; 56: 19-27
        • Forristall C.
        • Pondel M.
        • Chen L.
        • King M.L.
        Development. 1995; 121: 201-208
        • Kloc M.
        • Etkin L.D.
        Development. 1995; 121: 287-297
        • Mosquera L.
        • Forristall C.
        • Zhou Y.
        • King M.L.
        Development. 1993; 117: 377-386
        • Chang P.
        • Torres J.
        • Lewis R.A.
        • Mowry K.L.
        • Houliston E.
        • King M.L.
        Mol. Biol. Cell. 2004; 15: 4669-4681
        • Rebagliati M.R.
        • Weeks D.L.
        • Harvey R.P.
        • Melton D.A.
        Cell. 1985; 42: 769-777
        • Weeks D.L.
        • Melton D.A.
        Cell. 1987; 51: 861-867
        • Lustig K.D.
        • Kroll K.L.
        • Sun E.E.
        • Kirschner M.W.
        Development. 1996; 122: 4001-4012
        • Stennard F.
        • Carnac G.
        • Gurdon J.B.
        Development. 1996; 122: 4179-4188
        • Zhang J.
        • King M.L.
        Development. 1996; 122: 4119-4129
        • Claussen M.
        • Pieler T.
        Dev. Biol. 2004; 266: 270-284
        • Betley J.N.
        • Heinrich B.
        • Vernos I.
        • Sardet C.
        • Prodon F.
        • Deshler J.O.
        Curr. Biol. 2004; 14: 219-224
        • Messitt T.J.
        • Gagnon J.A.
        • Kreiling J.A.
        • Pratt C.A.
        • Yoon Y.J.
        • Mowry K.L.
        Dev. Cell. 2008; 15: 426-436
        • Yisraeli J.K.
        • Sokol S.
        • Melton D.A.
        Development. 1990; 108: 289-298
        • Yoon Y.J.
        • Mowry K.L.
        Development. 2004; 131: 3035-3045
        • White J.A.
        • Heasman J.
        J. Exp. Zoolog. B. Mol. Dev. Evol. 2008; 310: 73-84
        • Chan A.P.
        • Kloc M.
        • Etkin L.D.
        Development. 1999; 126: 4943-4953
        • Pannese M.
        • Cagliani R.
        • Pardini C.L.
        • Boncinelli E.
        Mech. Dev. 2000; 90: 111-114
        • Zearfoss N.R.
        • Chan A.P.
        • Wu C.F.
        • Kloc M.
        • Etkin L.D.
        Dev. Biol. 2004; 267: 60-71
        • Jambhekar A.
        • Derisi J.L.
        RNA. 2007; 13: 625-642
        • King M.L.
        • Messitt T.J.
        • Mowry K.L.
        Biol. Cell. 2005; 97: 19-33
        • Havin L.
        • Git A.
        • Elisha Z.
        • Oberman F.
        • Yaniv K.
        • Schwartz S.P.
        • Standart N.
        • Yisraeli J.K.
        Genes Dev. 1998; 12: 1593-1598
        • Deshler J.O.
        • Highett M.I.
        • Abramson T.
        • Schnapp B.J.
        Curr. Biol. 1998; 8: 489-496
        • Cote C.A.
        • Gautreau D.
        • Denegre J.M.
        • Kress T.L.
        • Terry N.A.
        • Mowry K.L.
        Mol. Cell. 1999; 4: 431-437
        • Zhao W.M.
        • Jiang C.
        • Kroll T.T.
        • Huber P.W.
        EMBO J. 2001; 20: 2315-2325
        • Kroll T.T.
        • Zhao W.M.
        • Jiang C.
        • Huber P.W.
        Development. 2002; 129: 5609-5619
        • Czaplinski K.
        • Köcher T.
        • Schelder M.
        • Segref A.
        • Wilm M.
        • Mattaj I.W.
        Dev. Cell. 2005; 8: 505-515
        • Claussen M.
        • Horvay K.
        • Pieler T.
        Development. 2004; 131: 4263-4273
        • Hudson C.
        • Woodland H.R.
        Mech. Dev. 1998; 73: 159-168
        • Allen L.
        • Kloc M.
        • Etkin L.D.
        Differentiation. 2003; 71: 311-321
        • Zhou Y.
        • King M.L.
        Dev. Biol. 1996; 179: 173-183
        • Kress T.L.
        • Yoon Y.J.
        • Mowry K.L.
        J. Cell Biol. 2004; 165: 203-211
        • Lewis R.A.
        • Gagnon J.A.
        • Mowry K.L.
        Mol. Cell. Biol. 2008; 28: 678-686
        • Allison R.
        • Czaplinski K.
        • Git A.
        • Adegbenro E.
        • Stennard F.
        • Houliston E.
        • Standart N.
        RNA. 2004; 10: 1751-1763
        • Zhang Q.
        • Yaniv K.
        • Oberman F.
        • Wolke U.
        • Git A.
        • Fromer M.
        • Taylor W.L.
        • Meyer D.
        • Standart N.
        • Raz E.
        • Yisraeli J.K.
        Mech. Dev. 1999; 88: 101-106
        • Kolev N.G.
        • Huber P.W.
        Mol. Cell. 2003; 11: 745-755
        • Alarcón V.B.
        • Elinson R.P.
        J. Cell Sci. 2001; 114: 1731-1741
        • Heasman J.
        • Wessely O.
        • Langland R.
        • Craig E.J.
        • Kessler D.S.
        Dev. Biol. 2001; 240: 377-386
        • Kloc M.
        • Etkin L.D.
        Science. 1994; 265: 1101-1103
        • Kloc M.
        • Wilk K.
        • Vargas D.
        • Shirato Y.
        • Bilinski S.
        • Etkin L.D.
        Development. 2005; 132: 3445-3457
        • Good P.J.
        Proc. Natl. Acad. Sci. U.S.A. 1995; 92: 4557-4561
        • Hinman M.N.
        • Lou H.
        Cell Mol. Life Sci. 2008; 65: 3168-3181
        • Bhattacharyya S.N.
        • Habermacher R.
        • Martine U.
        • Closs E.I.
        • Filipowicz W.
        Cell. 2006; 125: 1111-1124
        • Colegrove-Otero L.J.
        • Devaux A.
        • Standart N.
        Mol. Cell. Biol. 2005; 25: 9028-9039
        • Horvay K.
        • Claussen M.
        • Katzer M.
        • Landgrebe J.
        • Pieler T.
        Dev. Biol. 2006; 291: 1-11
        • Rupp R.A.
        • Snider L.
        • Weintraub H.
        Genes Dev. 1994; 8: 1311-1323
        • Koebernick K.
        • Hollemann T.
        • Pieler T.
        Dev. Biol. 2003; 260: 325-338
        • Git A.
        • Standart N.
        RNA. 2002; 8: 1319-1333
        • Ho S.N.
        • Hunt H.D.
        • Horton R.M.
        • Pullen J.K.
        • Pease L.R.
        Gene. 1989; 77: 51-59
        • Lisbin M.J.
        • Gordon M.
        • Yannoni Y.M.
        • White K.
        Genetics. 2000; 155: 1789-1798
        • Evans J.P.
        • Kay B.K.
        Methods Cell Biol. 1991; 36: 133-148
        • Abe S.
        • Davies E.
        Memoirs of the College of Agriculture. Vol. 31. Ehime University, Ehime, Japan1986: 187-199
        • Görg A.
        • Weiss W.
        • Dunn M.J.
        Proteomics. 2004; 4: 3665-3685
        • Jahn O.
        • Hesse D.
        • Reinelt M.
        • Kratzin H.D.
        Anal. Bioanal. Chem. 2006; 386: 92-103
        • Werner H.B.
        • Kuhlmann K.
        • Shen S.
        • Uecker M.
        • Schardt A.
        • Dimova K.
        • Orfaniotou F.
        • Dhaunchak A.
        • Brinkmann B.G.
        • Möbius W.
        • Guarente L.
        • Casaccia-Bonnefil P.
        • Jahn O.
        • Nave K.A.
        J. Neurosci. 2007; 27: 7717-7730
        • Reumann S.
        • Babujee L.
        • Ma C.
        • Wienkoop S.
        • Siemsen T.
        • Antonicelli G.E.
        • Rasche N.
        • Lüder F.
        • Weckwerth W.
        • Jahn O.
        Plant Cell. 2007; 19: 3170-3193
        • Livak K.J.
        • Schmittgen T.D.
        Methods. 2001; 25: 402-408
        • Mowry K.L.
        Proc. Natl. Acad. Sci. U.S.A. 1996; 93: 14608-14613
        • Chung S.
        • Jiang L.
        • Cheng S.
        • Furneaux H.
        J. Biol. Chem. 1996; 271: 11518-11524
        • Yisraeli J.K.
        • Melton D.A.
        Nature. 1988; 336: 592-595
        • Kloc M.
        • Etkin L.D.
        Richter J.D. A Comparative Methods Approach to the Study of Oocytes and Embryos. Oxford University Press Inc., Oxford, UK1999: 256-278
        • Harland R.M.
        Methods Cell Biol. 1991; 36: 685-695
        • Hollemann T.
        • Panitz F.
        • Pieler T.
        Richter J.D. A Comparative Methods Approach to the Study of Oocytes and Embryos. Oxford University Press Inc., Oxford, UK1999: 279-290
        • Rudt F.
        • Pieler T.
        EMBO J. 1996; 15: 1383-1391
        • Ladomery M.
        • Wade E.
        • Sommerville J.
        Nucleic Acids Res. 1997; 25: 965-973
        • Tanaka K.J.
        • Ogawa K.
        • Takagi M.
        • Imamoto N.
        • Matsumoto K.
        • Tsujimoto M.
        J. Biol. Chem. 2006; 281: 40096-40106
        • Devaux A.
        • Colegrove-Otero L.J.
        • Standart N.
        FEBS Lett. 2006; 580: 4947-4952
        • Atasoy U.
        • Watson J.
        • Patel D.
        • Keene J.D.
        J. Cell Sci. 1998; 111: 3145-3156
        • Fan X.C.
        • Steitz J.A.
        Proc. Natl. Acad. Sci. U.S.A. 1998; 95: 15293-15298
        • Chekulaeva M.
        • Hentze M.W.
        • Ephrussi A.
        Cell. 2006; 124: 521-533
        • Minshall N.
        • Standart N.
        Nucleic Acids Res. 2004; 32: 1325-1334
        • Nakamura A.
        • Amikura R.
        • Hanyu K.
        • Kobayashi S.
        Development. 2001; 128: 3233-3242
        • Marnef A.
        • Sommerville J.
        • Ladomery M.R.
        Int. J. Biochem. Cell Biol. 2009; 41: 977-981
        • Brennan C.M.
        • Steitz J.A.
        Cell Mol. Life Sci. 2001; 58: 266-277
        • Gorospe M.
        Cell Cycle. 2003; 2: 412-414
        • Dormoy-Raclet V.
        • Ménard I.
        • Clair E.
        • Kurban G.
        • Mazroui R.
        • Di Marco S.
        • von Roretz C.
        • Pause A.
        • Gallouzi I.E.
        Mol. Cell. Biol. 2007; 27: 5365-5380
        • Condeelis J.
        • Singer R.H.
        Biol. Cell. 2005; 97: 97-110
        • Atlas R.
        • Behar L.
        • Sapoznik S.
        • Ginzburg I.
        J. Neurosci. Res. 2007; 85: 173-183
        • Aronov S.
        • Aranda G.
        • Behar L.
        • Ginzburg I.
        J. Neurosci. 2001; 21: 6577-6587