Regulation of transcription of genes of ribosomal rna during amphibian oogenesis. A biochemical and morphological study.

Abstract

Natural changes in the transcription of rRNA genes were studied in nucleoli from three oogenic stages of the newt Triturus alpestris with electron microscope, autoradiographic, and biochemical techniques. From determinations of the uridine triphosphate pool sizes and [SH]uridine uptake, phosphorylation, and incorporation into 28S and 18S rRNAs in vivo it was estimated that the rate of rRNA synthesis was about 0.01% in previtellogenic oocytes and 13% in mature oocytes when compared to midvitellogenesis. Spread preparations of nucleoli showed significant morphological changes in the transcriptional complexes. The total number of lateral fibrils, i.e., ribonucleoproteins containing the nascent rRNA precursor, were drastically decreased in stages of reduced synthetic activity. This indicates that rRNA synthesis is regulated primarily at the level of transcription. The resulting patterns of fibril coverage of the nucleolar chromatin axes revealed a marked heterogeneity. On the same nucleolar axis occurred matrix units that were completely devoid of lateral fibrils, matrix units that were almost fully covered with lateral fibrils, and various forms of matrix units with a range of lateral fibril densities intermediate between the two extremes. Granular particles that were tentatively identified as RNA polymerase molecules were not restricted to the transcriptional complexes. They were observed, although less regularly and separated by greater distances, in untranscribed spacer regions as well as in untranscribed gene intercepts. The results show that the pattern of transcriptional control of rRNA genes differs widely in different genes, even in the same genetic unit.

20β-hydroxysteroid dehydrogenase and CYP19A1 are differentially expressed during maturation in Atlantic cod (Gadus morhua)

“…High peaks in the range of about 100 nucleotides completely dwarfed the normally predominant 18S and 28S rRNA peaks characteristic of intact total RNA. A similar phenomenon was observed in early studies of Xenopus oocytes where first 5S rRNA and to a certain extent also protein components of the ribosomes were synthesized before a switch occurred to 18S and 28S RNA production later in oogenesis (Scheer et al 1976). A simple change in the extraction method from isopropanol precipitation to column purification removed the large peaks of presumably 5S rRNA and tRNA, but the seasonal trend in eef1a remained (Fig.…”

Changes of nucleosome frequency in nucleolar and non-nucleolar chromatin as a function of transcription: an electron microscopic study

“…In addition , the use of a detergent for the discrimination between nucleosome and RNA polymerase particles is illustrated . The numerous nucleoli and chromosome loops of amphibian 00-cytes are especially suitable for such studies, since pronounced natural variations in their transcriptional activity occur during oogenesis (for example , Davidson, 1976;Scheer, Trendelenburg and Franke, 1976b) and an inhibition of transcription of both classes of genes can be induced in relatively short times by treatment with drugs (for example , Snow and Callan, 1969;Scheer , Trendelenburg and Franke, 1975;Rungger and Crippa , 1977) . The results of the present study show that there is a lag period before nontranscribed regions assume the nucleosomal configuration and support the concept that the condensation of DNA into nucleosomal particles is characteristic of inactive chromatin .…”

Frequencies of Circular Units of Nucleolar DNA in Oocytes of Two Insects, Acheta domesticus and Dytiscus marginalis, and Changes of Nucleolar Morphology during Oogenesis

“…also the dispersion and condensation cycle of amplified nucleolar material during amphibian oogenesis; for refs. see [17]). …”

“…these units, and (3) "light" regions with only very loosely packed, thin filaments that may correspond to the "cavities" or "vacuolizations" described in other forms of nucleoli (for refs. see [17,43,50]). Within this large "nucleolar aggregate", usually somewhat excentrically located, one often identifies a dense "core" body of a characteristic complex architecture (for details see Figs.…”

“…Selective amplification of rDNA has also been reported in nuclei of proliferating cells and plasmodia, for example the macronucleus of the ciliate, Tetrahymena pyriformiS [6][7][8], in the plasmodia of the slime mold, Physarum polycephalum [9] and in somatic amphibian cells [10]. Detailed molecular biological studies have shown that such amplified rDNA gene units can occur both in apparently linear molecules (see in particular Tetrahymena pyriformis [11,12]) and in covalently closed circles of different Differentiation 7,133-158 (1977) -© by Springer-VerJag 1977 sizes that contain variable numbers of pre-rRNA genes (amphibia [10, [13][14][15][16][17]; insects [18][19][20]; slime molds [9]; Tetrahymena [7]). In these studies it has further been demonstrated that relatively small circular units containing only a few (up to ten) genes can occur side by side with usually longer linear molecules in one and the same cell system.…”