Figure 2.

Nucleolar localization of wild-type U17 snoRNA injected into X. laevis oocytes. Fluorescein-labeled wild-type U17 snoRNA or spliceosomal U2 snRNA as a control was injected into the nuclei of X. laevis oocytes. After 1.5 h, nucleoli were prepared and analyzed by phase-contrast (PC) or fluorescence (FL) microscopy. The nucleolar rDNA is stained (DAPI, blue). Injection at an amount of 0.9 ng per oocyte (100%) resulted in a strong nucleolar labeling by U17 snoRNA but not by U2 snRNA (FL, green). After dilution of U17, even 35% of this amount yields detectable nucleolar labeling 1.5 h after injection. Oocyte nucleoli vary in size (Wu and Gall, 1997) and can fuse into multinucleolar clusters (Shah et al., 1996). A lampbrush chromosome is visible by DAPI staining (see PC and DAPI panels for 70% of U17 injected). Bar, 10 μm.