The central portion of oskar 3′ UTR is necessary and sufficient for oocyte transport. (A) Schematic representation of the reporter constructs analyzed in this panel and their ability to localize to the oocyte portion of stage 5–6 egg-chambers. Red rectangle: region 2b encompassing the oocyte entry signal (OES), gray rectangle: TLS of fs(1)K10. Numbers indicate nucleotide positions within the oskar 3′ UTR. (B–K) Stage 5–6 egg-chambers from oskar RNA null flies (oskA87/Df(3R)pXT103) expressing transgenic oskar 3′ UTR variants fused to the egfp open reading frame and under the control of a yeast UAS. Reporter mRNAs were expressed by pCog-Gal4 and nos-Gal4 drivers and detected by fluorescent in situ hybridization with an egfp-antisense probe. The asterisk indicates the position of the oocyte nucleus. Bar, 30 μm. The effects on localization shown were fully penetrant in all scored egg-chambers (n ≥ 20). Reporter mRNAs were fused to: the complete oskar 3′ UTR (B); region 1 + 2 (C); region 2 + 3 (D); region 1 (E); region 3 (F); region 2 (G); region 2b + 3 of the oskar 3′ UTR (H); the complete oskar 3′ UTR bearing a deletion of region 2b (I); region 2b of the oskar 3′ UTR (J); region 3 fused at its 5′ end to the TLS of fs(1)K10 mRNA (K). (L,M) Experimentally validated secondary structures of the 44-nt-long TLS of fs(1)K10 mRNA (L) (Bullock et al. 2010) and of the 67-nt-long OES of oskar mRNA (M) (Jambor et al. 2011).
