The germinal vesicle of the Drosophila oocyte is transcriptionally quiescent during the latter part of the first meiotic prophase. Concomitant with silencing of the genome, the nucleolus disappears at an early stage and the chromatin condenses into a compact mass called the karyosome. A prominent Cajal body (endobody) is present during most of prophase, attached to the karyosome. Components of the U7 small nuclear (sn) RNP reside in a separate body, the histone locus body, which is also attached to the karyosome. The histone locus body is no longer detectable with probes for the U7 snRNP after about stage 5 of oogenesis. Several other nuclear bodies of unknown nature can be detected by phase contrast, differential interference contrast, and electron microscopy.
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