Fig. 1. Characterization of the osk^A87 and osk¹⁸⁷ alleles. (A) Schematic representation of the oskar locus and the insertion points of the transposable elements in the new oskar alleles. E1 through E4 represent the oskar exons. The first exon contains a 15 nucleotide untranslated region. In osk^A87, a ZAM retrotransposable element is inserted 51 bp upstream of the first intron, in reverse orientation relative to oskar. In osk¹⁸⁷, an I element is inserted 534 bp upstream of the oskar transcription initiation site, in the same orientation as oskar. (B,C) Northern blot and RT-PCR analysis of oskar mRNA in the new oskar mutants. (B) Northern blot: WT1 sample is RNA from wild-type (Oregon R) egg chambers of stages 1 to 14, and WT2 from wild-type egg chambers of stages 1 to 7-8. The egl^RC12 sample represents ovaries whose development arrested during oogenesis at stages similar to the new oskar mutants. osk⁵⁴ and osk⁸⁴ are nonsense alleles of oskar (Kim-Ha et al., 1991). Only trace amounts of oskar mRNA are detected in homozygous osk¹⁸⁷ egg chambers and no oskar mRNA is detected in osk¹⁸⁷/Df(3R)p^XT103 egg chambers. (C) RT-PCR: in contrast to bcd (upper panel), no oskar mRNA is detected by RT-PCR in osk^A87/Df(3R)p^XT103 egg chambers (lower panel, lane 2) while a 126 bp band is detected in a control amplification from nos^A10/Df(3R)p^XT103 (lower panel, lane 1), an allele of nanos originating from the same genetic background as osk^A87. Lanes 3: negative controls without addition of template. (D) oskar RNA in situ hybridization in osk¹⁸⁷ and osk^A87. Fluorescently-labeled antisense oskar RNA probe was used to visualize the presence of endogenous oskar RNA in stage 3-4 wild-type, osk¹⁸⁷/Df(3R)p^XT103 and osk^A87/Df(3R)p^XT103 mutant egg chambers. Compared with wild type, considerably less or no oskar RNA is detected in osk¹⁸⁷/Df(3R)p^XT103 and in osk^A87/Df(3R)p^XT103 egg chambers, respectively.