Staufen Recruitment into Stress Granules Does Not Affect Early mRNA Transport in Oligodendrocytes

Abstract

INTRODUCTIONFrom the early steps of mRNA transport to the latest events of degradation, cytoplasmic RNA granules are highly relevant to the physiology of mRNA, including silencing and activation (reviewed in Wickens and Goldstrohm, 2003). Granules packaging targeted mRNAs appear in oligodendrocytes and other polarized vertebrate cells as dense structures, containing also ribosomes and with an average diameter of 1 m ( Barbarese et al., 1995;Barry et al., 1996;Ainger et al., 1997;Knowles and Kosik, 1997;Carson et al., 2001;Krichevsky and Kosik, 2001). A different type of RNA granules known as stress granules (SGs) appears transiently upon induction of cellular stress. SGs are large ribonucleoparticles (RNPs) and are thought to be in dynamic equilibrium with translating polysomes (Kedersha et al., 2000Anderson and Kedersha, 2002).The double-stranded RNA-binding protein Staufen emerges as a relatively ubiquitous RNA granule-forming factor (Ferrandon et al., 1994;Duchaine et al., 2000; Kiebler and DesGrosseillers, 2000;Micklem et al., 2000). This protein was initially described in Drosophila oocytes, where it is found in granules involved in microtubule-dependent localization of maternal mRNAs to define the anterior-posterior axis of the embryo (Lasko, 1999;Kloc et al., 2002). Staufen is recruited into granules upon its interaction with bicoid mRNA 3ЈUTR sequences that mediate targeting of the messenger, and it is strictly required for the formation of these granules (Ferrandon et al., 1994(Ferrandon et al., , 1997. Likewise, the positioning of oskar mRNA at the oocyte posterior pole involves the formation of Staufen-containing granular structures known as polar bodies (Lasko, 1999;Kloc et al., 2002). Staufen also participates in actin-dependent segregation of prospero mRNA during asymmetric division of embryonic CNS cells (reviewed in Lasko, 1999; Kiebler and DesGrosseillers, 2000;Kloc et al., 2002). Moreover, Drosophila Staufen is essential for long-term memory acquisition, a phenomenon known to require mRNA targeting followed by local translation at the synapse (Dubnau et al., 2003).Two homologous genes, Staufen 1 and Staufen 2, were reported in mammalians and amphibians (Kiebler and DesGrosseillers, 2000;Monshausen et al., 2001;Tang et al., 2001;Kress et al., 2004;Yoon and Mowry, 2004 et al., , Kohrmann et al., 1999Macchi et al., 2003). Rat Staufen 1 binds to the dendrite targeting element (DTE) of MAP2 mRNA (Monshausen et al., 2001) and, in addition, Staufen 1 RNPs isolated from brain and cortical neurons contain localized RNAs and associate to motor molecules (Krichevsky and Kosik, 2001;Ohashi et al., 2002;Mallardo et al., 2003;Kanai et al., 2004). Furthermore, overexpression of a truncated form of Staufen 2 leads to a reduction of the dendritic RNA content (Tang et al., 2001). Likewise, interference strategies in amphibian oocytes indicates that Xenopus Staufen 1 is involved in the late localization pathway to the vegetal pole (Kress et al., 2004;Yoon and Mowry, 2004). In this study, we investigated the dist...

Dendritic Localization of the Translational Repressor Pumilio 2 and Its Contribution to Dendritic Stress Granules

“…The large granules that formed in the presence of puromycin were reminiscent of SGs. It has been reported that various cellular stresses, including puromycin treatment, induce the accumulation of a number of RNA-binding proteins such as Staufen (Thomas et al, 2005), FMRP (Mazroui et al, 2002), and elements of the translational machinery including PABP and eIF4E into SGs (Kedersha et al, 2005).…”

“…Recently, RNA-binding proteins such as fragile X mental retardation protein (FMRP), Staufen, and Smaug, which are involved in dendritic mRNA localization and translation, have been found to accumulate in stress granules (SGs) (Mazroui et al, 2002;Baez and Boccaccio, 2005;Thomas et al, 2005;Kim et al, 2006). This process occurs when cells are exposed to environmental stresses.…”

EGFP-FMRP Granules Are Proto-Granules That Can Be Shunted to Stress Granules During a Stress Response

“…Stress granules can be formed in response to heat shock (Mazroui et al, 2002), oxidative stress (Thomas et al, 2004), RNA binding protein over expression (Solomon et al, 2007), expression of a phosphomimetic mutant form of eukaryotic initiation factor 2 (eIF-2) (McEwen et al, 2005) and interfering with eIF4A activity (Mazroui et al, 2006). To determine whether the granules formed by expression of EGFP-FMRP were stress granules, rat pheochromocytoma cells (PC12) were transiently transfected with an EGFP-FMRP expression vector.…”

“…For presentation, granule size distributions were all normalized to 500 particles and the normalized distributions were compared using the Ftest for two sample variance. Protein co-localization measurements were performed by counting single-and double-stained granules of acquired images (Thomas et al, 2004). …”

Genome wide identification of Staufen2-bound mRNAs in embryonic rat brains

“…These proteins finely control the successive steps that insure proper expression of mRNA at specific times and space. Staufen2 (Stau2), a protein mainly expressed in brain is a well accepted player for mRNA localization (4)(5)(6)(7)(8)(9). In brain, Stau2 is expressed in several cell types including neurons and oligodendrocytes.…”