Nucleolar activity of germ cells in polytrophic ovaries of crane flies (Diptera: Tipulidae). Ultrastructural and cytochemical studies.
Ultrastructural and histochemical studies confirmed extrachromosomal amplification of rDNA in nuclei of the oocyte and one of its sibling nurse cells during early stages of oogenesis in Tipula spp. Decondensation of the extra DNA body in the oocyte nucleus coincides with the appearance of multiple nucleoli. In contrast, the amplified copies of ribosomal genes in the nurse cell nucleus remain condensed (i.e. transcriptionally inactive). Roughly of the same size, all nurse cells look almost identical. Their nuclei are spherical and contain single, prominent nucleoli, clumps of chromatin and accumulations of granular material. The cytoplasm is packed with free ribosomes, while in close vicinity of the nuclear envelope many islets of fine granular nuage material can be found. These data indicate that the nurse cells in crane fly ovaries are synthetically active, i.e. contribute to the overall production of ribosomes and their final accumulation in the oocyte. The invariable volume of the nurse cells throughout oogenesis may therefore result from the differences in the dynamics of transcriptional activity and transport of ribosomes, rather than indicate their low synthetic activity.
Mazurkiewicz
Marta
M
Department of General Zoology, Zoological Institute, University of Wrocław, Poland.
Kubrakiewicz
Janusz
J
D000818:Animals; D002466:Cell Nucleolus / Q000378:metabolism / Q000648:ultrastructure*; D004275:DNA, Ribosomal / Q000096:biosynthesis / Q000235:genetics / Q000648:ultrastructure*; D004175:Diptera / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure*; D005260:Female; D005456:Fluorescent Dyes; D005784:Gene Amplification / Q000235:genetics; D005854:Germ Cells / Q000378:metabolism / Q000648:ultrastructure*; D008854:Microscopy, Electron; D009866:Oogenesis / Q000235:genetics; D010053:Ovary / Q000378:metabolism / Q000648:ultrastructure*; D021381:Protein Transport / Q000235:genetics; D012335:RNA, Ribosomal / Q000096:biosynthesis / Q000235:genetics / Q000648:ultrastructure; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure*; D016622:Silver Staining; D014158:Transcription, Genetic / Q000502:physiology
D004275:DNA, Ribosomal; D005456:Fluorescent Dyes; D012335:RNA, Ribosomal