40LoVe interacts with Vg1RBP/Vera and hnRNP I in binding the Vg1-Localization Element

Abstract

Localizing mRNAs within the cytoplasm gives cells the ability to spatially restrict protein production, a powerful means to regulate gene expression. Localized mRNA is often visible in microscopically observable particles or granules, and the association of mRNA localization with these structures is an indication that particles or granules may be essential to the localization process. Understanding how such structures form will therefore be important for understanding the function of localization RNPs (L-RNPs). We previously identified a novel component of an L-RNP from the Vg1 mRNA from Xenopus oocytes called 40LoVe. 40LoVe interaction with the Vg1-localization element (Vg1LE) was previously shown to be dependent on the VM1 and E2 sequence motifs within the Vg1LE that cross-link to hnRNP I and Vg1RBP/Vera, respectively. We report interaction of these motif-binding proteins with 40LoVe and identify a 40LoVe-Xenopus hnRNP D/AUF1 interaction. We further demonstrate that titration of VM1 and E2 motif binding activity in vivo surprisingly suggests that the motif binding proteins have differing roles during Vg1LE-dependent mRNA localization.

Cis-acting determinants of asymmetric, cytoplasmic RNA transport

“…Creating a high-density cluster of one protein via multimerization of its binding site may recruit other essential proteins to the mRNP via protein-protein, rather than protein-RNA, interactions. In support of this possibility, clusters of VM1 and E2 sites in Vg1 RNA recruit 40LoVe, a component of the localizing mRNP (Czaplinski and Mattaj 2006). Arn et al (2003) have proposed that specific RNA recognition involves multiple low-affinity and low-specificity interactions that can occur either on a complex RNA target or on tandem repeats of a minimal recognition element.…”

“…It is not clear whether depolarization causes a conformational change in the RNA itself, a change in the expression/activity of any trans-acting factors, or both. Analogous to the putative transport repressors in aCaMKII, the VM1 sites in the Vg1 zipcode have been proposed to repress transport, since injection of VM1-containing repeat RNA (which titrates out hnRNP I) enhanced Vg1 localization (Czaplinski and Mattaj 2006). Conclusive demonstration of cis-acting inhibitors of transport awaits isolation of sequences that can prevent localization out of context of their native RNAs.…”

“…Translational control has been reviewed elsewhere (e.g., Bashirullah et al 1998;Johnstone and Lasko 2001;Kindler et al 2005;Sossin and Desgroseillers 2006) and will not be discussed here. Additional RNA sequences may be required to promote the assembly of a localization-competent RNP (Czaplinski and Mattaj 2006). …”

Hnrpab regulates neural development and neuron cell survival after glutamate stimulation

“…In fact, evolutionarily conservation of the Hnrpab protein strongly supports this as cellular role for Hnrpab function. Injecting antibodies into the Xenopus Hnrpab ortholog, 40LoVe, impairs localization of the TGF-b family Vg1 mRNA in the cytoplasm of oocytes, and the Drosophila relative, called Squid, plays a role in localization of different mRNAs during Drosophila oogenesis (Norvell et al 1999;Czaplinski et al 2005;Czaplinski and Mattaj 2006;Delanoue et al 2007). Recombinant Hnrpab2 was suggested to have a detectable preference for an hnRNP A2 responsive element (A2RE), an RNA sequence involved in mRNA transport in oligodendrocytes and neurons, although this particular sequence was demonstrated to bind quite specifically to hnRNP A2 (Hoek et al 1998;Raju et al 2008).…”

RNA localization to the Balbiani body in Xenopus oocytes is regulated by the energy state of the cell and is facilitated by kinesin II

“…Thus, the ability to recruit kinesin II is an inherent property of this RNA localization element and occurs throughout all stages of oogenesis in which RNA localization takes place (Betley et al 2004). Since a number of in vivo competition studies indicate that RNA localization factors in Xenopus oocytes are in a large excess relative to microinjected RNA (Kwon et al 2002;Choo et al 2005;Czaplinski and Mattaj 2006), it is expected that detecting the enrichment of such factors in the Balbiani body would require more time than detecting enrichment of the RNA that recruits it (see Materials and Methods).…”