gurken and the I Factor Retrotransposon RNAs Share Common Localization Signals and Machinery

Abstract

Drosophila gurken mRNA is localized by dynein-mediated transport to a crescent near the oocyte nucleus, thus targeting the TGFalpha signal and forming the primary embryonic axes. Here, we show that gurken and the I factor, a non-LTR retrotransposon, share a small consensus RNA stem loop of defined secondary structure, which forms a conserved signal for dynein-mediated RNA transport to the oocyte nucleus. Furthermore, gurken and the I factor compete in vivo for the same localization machinery. I factor transposition leads to its mRNA accumulating near and within the oocyte nucleus, thus causing perturbations in gurken and bicoid mRNA localization and axis specification. These observations further our understanding of the close association of transposable elements with their host and provide an explanation for how I factor transposition causes female sterility. We propose that the transposition of other elements may exploit the host's RNA transport signals and machinery.

Cis-acting determinants of asymmetric, cytoplasmic RNA transport

“…The predicted secondary structure of this element is similar to that of a zipcode derived from the I factor transcript, an LTR RNA whose localization during stages 8-9 parallels that of grk (Van De Bor et al 2005). While Van de Bor and colleagues did not report a role for the grk 39 UTR in directing localization (Van De Bor et al 2005), two other studies reported that the 39 UTR was necessary for the final stages of anterodorasal accumulation (Saunders and Cohen 1999;Thio et al 2000). This discrepancy was attributed to differences in reporters used for assaying localization (Van De Bor et al 2005).…”

“…This discrepancy was attributed to differences in reporters used for assaying localization (Van De Bor et al 2005). All three studies agreed that the 39 UTR of grk, unlike that of several other transcripts localized in Drosophila oocytes, has no localization activity on its own (Saunders and Cohen 1999;Thio et al 2000;Van De Bor et al 2005).…”

“…While Van de Bor and colleagues did not report a role for the grk 39 UTR in directing localization (Van De Bor et al 2005), two other studies reported that the 39 UTR was necessary for the final stages of anterodorasal accumulation (Saunders and Cohen 1999;Thio et al 2000). This discrepancy was attributed to differences in reporters used for assaying localization (Van De Bor et al 2005). All three studies agreed that the 39 UTR of grk, unlike that of several other transcripts localized in Drosophila oocytes, has no localization activity on its own (Saunders and Cohen 1999;Thio et al 2000;Van De Bor et al 2005).…”

“…Two transcripts that are localized to the dorsoanterior corner of Drosophila oocytes, grk and I factor, share similar hairpin zipcodes that function during stage 8 of oogenesis (see above) (Van De Bor et al 2005). While both zipcodes contain three stem regions separated by two internal bulged loops, the precise stem lengths, bulge sizes and locations, and terminal loop lengths differ, as do the nucleotide identities.…”

Preparing Individual <em>Drosophila</em> Egg Chambers for Live Imaging

“…For early-and mid-stage egg chambers, mounting in halocarbon oil is good for survival in that it allows free diffusion of oxygen, prevents dehydration and hypoxia and has superb optical properties for microscopy. Imaging of fluorescent proteins is possible through the introduction of transgenes into the egg chamber or physical injection of labeled RNA, protein or antibodies [5][6][7] . For example, addition of MS2 constructs to the genome of animals enables real time observation of mRNAs in the oocyte 8 .…”