Showing papers on "Nucleolus published in 1982"
TL;DR: In addition to its previously characterized, six different polypeptide components, signal recognition protein—which functions in protein translocation across and integration into the endoplasmic reticulum membrane—contains a 7S RNA molecule that is required for both structural and functional properties of signal recognition particle.
Abstract: In addition to its previously characterized, six different polypeptide components, signal recognition protein--which functions in protein translocation across and integration into the endoplasmic reticulum membrane--contains a 7S RNA molecule. The RNA is closely identified with the small cytoplasmic 7SL RNA and is required for both structural and functional properties of signal recognition protein--which we therefore rename signal recognition particle.
701 citations
TL;DR: Examination of oocytes of Xenopus laevis shows that the large extrachromosomal nucleoli are heavily stained with the Ag technique and that the Ag deposits are largely enriched in, if not exclusive to, the internal, fibrillar region.
148 citations
TL;DR: The results of immunocytochemical studies, using 4 of these monoclonal antibodies and immunoperoxidase detection methods, document the exclusively intranuclear localization of DNA polymerase alpha in three separate lines of cultured human cells.
142 citations
TL;DR: The mechanism by which some RNAs are segregated in the cell nucleus was analysed by microinjecting 32P-labelled total RNA from HeLa cells into the cytoplasm of Xenopus oocytes, showing that the migrating RNAs become associated with oocyte RNA-binding proteins.
Abstract: The mechanism by which some RNAs are segregated in the cell nucleus was analysed by microinjecting 32P-labelled total RNA from HeLa cells into the cytoplasm of Xenopus oocytes. Small nuclear RNAs (U1, U2, U4, U5 and U6) migrated into the cell nucleus, where they became 30–60 fold more concentrated than in the cytoplasm. Other RNAs, such as tRNA and 7S RNA, remained in the cytoplasm, while 5S RNA became concentrated in the nucleolus. Studies with lupus erythematosus antibodies showed that the migrating RNAs become associated with oocyte RNA-binding proteins.
127 citations
TL;DR: It is suggested that the Aegilops umbellulata nucleolus organisers are dominant over those of wheat because they compete more effectively for some limiting factor.
Abstract: Two pairs of chromosomes (1U and 5U) in Aegilops umbellulata possess ribosomal RNA genes. This has been proven by studying wheat plants into which 1U and 5U chromosomes have been introduced separately. These plants have more ribosomal RNA genes than the recipient wheat plants and additional clusters of rDNA when examined by in situ hybridisation. The repeating rDNA unit in Aegilops umbellulata is longer than most of the units in the wheat variety Chinese Spring, the additional DNA probably being in the non-transcribed spacer. This was determined from restriction endonuclease maps of rDNA. In Chinese Spring plants possessing 1U or 5U chromosomes, the largest nucleoli are formed on 1U or 5U chromosomes and the wheat nucleolus organisers form micronucleoli. This is not because the nucleolus organisers on chromosomes 1U and 5U have many more rRNA genes than wheat nucleolus organisers. It is suggested that the Aegilops umbellulata nucleolus organisers are dominant over those of wheat because they compete more effectively for some limiting factor. — The partial inactivation of the wheat nucleolus organisers by chromosomes 1U or 5U does not result in a reduced total nucleolus volume in root tip or pollen mother cells, because of the compensation by the nucleolus organisers of chromosomes 1U or 5U. The amount of RNA in seedlings is not markedly affected by the partial inactivation of the wheat nucleolus organisers.
87 citations
TL;DR: The qualitative analysis of the Ag-stainability of the NORs was in very good agreement with the results obtained for mammals: Ag-stained NORs are detectable during the entire meiotic prophase up to the pachytene stage, completely absent in the meiotic metaphases I and II, and again demonstrable in early spermatid nuclei.
Abstract: The patterns of activity of the nucleolus organizer regions (NORs) in the spermatogeneses of ten species of all non-mammalian classes of vertebrates and one species of the cephalochordates were investigated with the silver (Ag)-staining technique. The Ag-stainability of the NORs is a measure of the transcriptional activity of the ribosomal RNA genes. In all species, there is a very similar pattern of NOR-activity in the various stages of Spermatogenesis. The qualitative analysis of the Ag-stainability of the NORs was in very good agreement with the results obtained for mammals: Ag-stained NORs are detectable during the entire meiotic prophase up to the pachytene stage, completely absent in the meiotic metaphases I and II, and again demonstrable in early spermatid nuclei. The results confirm the occurrence of postmeiotic reactivation of the RNA genes. The preferential inhibition of rRNA synthesis by low doses of actinomycin D induced a rapid decline of the Ag-stainability of the postmeiotically reactivated NORs. The significance of the evolutionary conservation of the postmeiotic NOR-reactivation is discussed.
78 citations
Journal Article•
TL;DR: It is thought that FCs are not the whole interphasic counterpart of the mitotic nucleolar organizing region (NOR), but only the portion of the NOR that is temporarily inactive in transcription; the transcriptionally active part of theNOR is in the fibrillar component, bound to its earliest product of transcription.
Abstract: In plant cells nucleolar fibrillar centres (FCs) undergo ultrastructural changes, depending on the nucleolar activity. We have found two types of FC structure in nucleoli with either high or low activity, to which we have given the conventional names of homogeneous and heterogeneous, respectively. The first type is characterized by the presence of fibres that we describe structurally and cytochemically as decondensed chromatin; the second type, in addition to these fibres, contains a variable number of dense cores made up of condensed chromatin. Moreover, RNA does not appear to be present in FCs, while proteins are a major component. Autoradiography after tritiated uridine incorporation shows that FCs are not the site of transcription, but that this takes place in the fibrillar component; the same result is obtained using the lead acetate fixation technique for detecting orthophosphate ions. This fact leads us to think that FCs are not the whole interphasic counterpart of the mitotic nucleolar organizing region (NOR), as stated by other authors, but only the portion of the NOR that is temporarily inactive in transcription; the transcriptionally active part of the NOR is in the fibrillar component, bound to its earliest product of transcription. Thus, FCs and the fibrillar component constitute a functional unit.
75 citations
TL;DR: An antibody has been raised to Tetrahymena histone variant hv1 that specifically stains the macron nucleus, but not the micronucleus, of TetrahYmena, suggesting that this histone variants has been highly conserved in evolution and may be associated with transcribed sequences.
65 citations
TL;DR: In this article, a positive localization of a karyoskeletal protein in the nuclear interior of Xenopus oocytes was reported, i.e. away from the pore complex-lamina structure of the nuclear cortex.
Abstract: Oocyte nuclei of Xenopus laevis contain two major karyoskeletal proteins characterized by their resistance to extractions in high salt buffers and the detergent Triton X-100, i.e. a polypeptide of 68,000 mol wt which is located in the core complex-lamina structure and a polypeptide of 145,000 mol wt enriched in nucleolar fractions. Both proteins are also different by tryptic peptide maps and immunological determinants. Mouse antibodies were raised against insoluble karyoskeletal proteins from Xenopus oocytes and analyzed by immunoblotting procedures. Affinity purified antibodies were prepared using antigens bound to nitrocellulose paper. In immunofluorescence microscopy of Xenopus oocytes purified antibodies against the polypeptide of 145,000 mol wt showed strong staining of nucleoli, with higher concentration in the nucleolar cortex, and of smaller nucleoplasmic bodies. In various other cells including hepatocytes, Sertoli cells, spermatogonia, and cultured kidney epithelial cells antibody staining was localized in small subnucleolar granules. The results support the conclusion that this "insoluble" protein is a major nucleus-specific protein which is specifically associated with--and characteristic of--nucleoli and certain nucleolus-related nuclear bodies. It represents the first case of a positive localization of a karyoskeletal protein in the nuclear interior, i.e. away from the pore complex-lamina structure of the nuclear cortex.
65 citations
TL;DR: Application of NOR silver staining to Pleurodeles oocyte nuclei showed selective silver deposits on the fibrillar part of the nucleoli in situ, and proteins seemed preferentially located on the DNP axis rather than on the RNP fibrils.
Abstract: Application of NOR silver staining to Pleurodeles oocyte nuclei showed selective silver deposits on the fibrillar part of the nucleoli in situ. This staining was adapted to nucleoli spread on grids, by a procedure which allowed the spreading of transcription units from both nucleoli and lampbrush chromosomes on the same grids. This permitted localization of the predominant nucleolar Ag-stained proteins on the nucleolar transcriptional units and not on the lampbrush chromosomes. These proteins were found exclusively on the transcribed part of the nucleolar genes and were not seen in apparently untranscribed spacer regions. The proteins seemed preferentially located on the DNP axis rather than on the RNP fibrils.
58 citations
TL;DR: Protein C23 (Mr = 110,000; pI, 5.5) is the major phosphoprotein in the nucleolus of Novikoff hepatoma cells and comprises 9.5% of the total nucleolar protein.
TL;DR: The changes in size and structure of the nucleolus taking place during the migration of columnar cells can be correlated with the maturation of the cells and the loss of their ability to synthesize ribosomal RNA.
Abstract: An image analyser was used to measure the area of the nucleolus and its component parts in columnar cells at six levels of the jejunal epithelium, corresponding to stages in cell migration from crypt base to villus top In columnar cells of crypt base, which function as stem cells for the epithelium, the nucleolus is large (31 micron2), irregular and reticulated As cells migrate up the crypt, divide and differentiate, the nucleolus decreases in size (17 micron2) and becomes spherical, but remains reticulated In the fully differentiated cells of the midvillus, however, the nucleolus becomes small (09 micron2) and compact At the villus top, as the cells display early signs of degeneration, the nucleolus is further compacted (05 micron2) Most nucleolar components also decrease in size Pars fibrosa (about 19% of the nucleolar area in crypt base) and pars granulosa (about 70%) decrease in proportion to the rest of the nucleolus, except in mid-villus and villus top where loss of pars granulosa predominates In contrast, the total area of fibrillar centres remains constant (about 01 micron2), even though individual centres are small and numerous in crypt base, larger and fewer at higher levels, and they coalesce into a single structure in villus top The other nucleolar components are also segregated into distinct, but adjacent, areas at this level The changes in size and structure of the nucleolus taking place during the migration of columnar cells can be correlated with the maturation of the cells and the loss of their ability to synthesize ribosomal RNA
TL;DR: The silver impregnation technique clearly demonstrates that two main components are responsible for the argentophily of the nucleolus.
Abstract: Hela cells were impregnated with silver according to Paweletz et al. (1967). In cells in mitosis not only the nucleolar organizer regions (NORs) are strongly impregnated but also part of the nucleolar material, which accumulates in and around the chromosomes. The treatment with adenosine, which in interphase cells spreads the nucleolar material within the nucleus, also distributes the argentophilic material in and around the chromosomes. During the reconstruction phase this material reassembles around the NORs to form parts of the new nucleolus. The silver impregnation technique clearly demonstrates that two main components are responsible for the argentophily of the nucleolus. This is in agreement with the results obtained by Lischwe et al. (1979).
Journal Article•
TL;DR: The method for electron microscopy of the Ag-staining of NOR-specific proteins was adapted to tissue sections from solid organs and it was concluded that in interphase nucleoli the Ag -staining NOR proteins are associated with the fibrillar components and with the derived nucleolar fibrillsar remnants.
TL;DR: The concept that an internal proteinaceous network is part of the isolated nuclear matrix and that this intranuclear structure represents a framework that exists in vivo is supported.
TL;DR: It is concluded that, at least in reticulated nucleoli, there is no numerical relationship between theNumber of fibrillar centres and the number of NORs, and that the fibrillsar centers cannot be considered only as the nucleolar counterparts of the NORs.
Abstract: In mouse testis, the diploid Sertoli cell displays one large nucleolus flanked symmetrically by two heterochromatic masses. The hybridization in situ with [3H]rRNA confirmed that the ribosomal cistrons are localized with in the central nucleolar mass. At the ultrastructural level this nucleolar mass appears to be reticulated and contains numerous fibrillar centres. These fibrillar centres are surrounded and interconnected by an electron-opaque fibrillar network, which constitutes the reticulated nucleolonema of the nucleolus. Ag—NOR staining reveals the presence of the argyrophilic proteins associated with active nucleolus-organizing regions (NORs) within both the fibrillar centres and the electron-opaque fibrillar component. Autoradiographic studies after [3H]uridine incorporation show that ribosomal DNA transcription only takes place in this dense fibrillar component. Three-dimensional reconstruction of four Sertoli cell nucleoli after serial sectioning reveals that the size and number of the fibrillar centers are very variable from one cell to another (26, 35, 38 an 41 fibrillar centres). The analysis of the volume occupied by the fibrillar centres as compared to the whole nucleolar volume demonstrates that the larger the nucleolus, the more fibrillar centres it contains, but also the more numerous the fibrillar centres, the larger their total volume. While in each case the number of the NORs is virtually the same, i.e. ten. In the light of these results we concluded that, at least in reticulated nucleoli, there is no numerical relationship between the number of fibrillar centres and the number of NORs, and that the fibrillar centers cannot be considered only as the nucleolar counterparts of the NORs. Moreover, the increasing number of fibrillar centres from the smallest nucleolus to the largest one is difficult to explain by the previously postulated hypothesis of a reserve of inactive rDNA packaged in the fibrillar centers. These data led us to reconsider the role of the fibrillar centres in the transcriptional activity of reticulated nucleoli.
TL;DR: It is suggested that the pattern of nucleolar fusion is determined in part by the position of the organizers in the nucleus, and their positions are altered in these ditelosomic stocks.
Abstract: Two pairs of major nucleoli form in cells of the wheat variety Chinese Spring and these frequently fuse during the cell cycle. The volume of the nucleolus formed at the organizer on chromosome 1B is approximately twice the volume of the nucleolus formed at the organizer on chromosome 6B. The volumes of fused nucleoli are distributed around the additive means expected if the nucleoli of the two different sizes fused in all possible combinations. Thus nucleolar volume but not the surface area is additive on fusion. Four nucleoli can fuse to produce nuclei with nine different nucleolar patterns. All nine were found but the frequencies of the different fusion classes were different in different genotypes. The frequencies in euploid Chinese Spring and tetrasomic 3B showed small deviations from those expected if fusion between different nucleoli occurred with equal frequency, but in the aneuploids DT 5 B L and DT 5 A L the fusion of heterologous nucleoli from chromosome 1B and 6B organizers occurred with a much higher frequency. It is suggested that the pattern of nucleolar fusion is determined in part by the position of the organizers in the nucleus, and their positions are altered in these ditelosomic stocks.
Journal Article•
TL;DR: The finding that persistent foci continued to display ultrastructural abnormalities, some of which changed or progressed in the absence of further carcinogen exposure, suggests that the persistent iron-excluding foci are a permanently altered population.
Abstract: Hepatocellular altered foci were induced in rat liver by cycles of feeding of N-2-fluorenylacetamide and were distinguished by their resistance to iron accumulation following production of hepatic siderosis by dietary administration of 8-hydroxyquinoline and ferrous gluconate. The foci were readily identified by their iron exclusion in plastic-embedded sections stained for iron. Sections from iron-free regions processed for electron microscopy permitted ultrastructural study of cells in foci identified by reduced cytoplasmic ferritin. Altered foci of the eosinophilic type produced by cyclic feeding of carcinogen for 16 weeks were composed of both normal-appearing hepatocytes and others with ultrastructural abnormalities, including increased agranular reticulum with associated glycogen particles, decreased rough endoplasmic reticulum with reduced length of cisternae, degranulated rough vesicles, altered and displaced Golgi complexes, and abnormal bile canaliculi. At 12 and 24 weeks after cessation of carcinogen exposure, cells in persistent eosinophilic foci continued to display ultrastructural abnormalities. They possessed increased rough endoplasmic reticulum with rather regular cisternal arrangement and relatively increased smooth endoplasmic reticulum. Golgi complexes were abnormal. Bile canaliculi were abnormal and occasionally increased in number. Nuclei displayed prominent nucleoli. Cells in a basophilic focus were characterized by the presence of numerous free polyribosomes diffusely scattered throughout the cytoplasm, distended rough endoplasmic reticulum with loss of parallel-stack and hypertrophic dilated Golgi complexes, and prominent marginated nucleoli. The finding that persistent foci continued to display ultrastructural abnormalities, some of which changed or progressed in the absence of further carcinogen exposure, suggests that the persistent iron-excluding foci are a permanently altered population.
TL;DR: The nucleoli of lymphocytes undergo a typical sequence of structural changes after stimulation by phytohaemagglutinin, but these changes are independent of the cell cycle.
Abstract: The nucleoli of lymphocytes undergo a typical sequence of structural changes after stimulation by phytohaemagglutinin. These changes are independent of the cell cycle. Neither the inhibition of DNA-synthesis (by adenosine and methotrexate), nor the elimination of postmitotic interphase nuclei (by a colchicine block of mitoses), nor the release from such blocks has a noticeable effect on nucleolar structure or on the sequence of nucleolar changes. The number of nucleoli per cell is clearly influenced by the cell cycle. Mitosis leads to a marked increase in the number of nucleoli, whereas in all stages of interphase a decrease occurs.
TL;DR: In porcine thyroid cells cultivated in vitro, thyrotropin stimulation resulted in formation of nucleolar buds which subsequently detached themselves, giving rise to nuclear bodies, a finding which formally demonstrated the nucleolar origin of nuclear bodies.
TL;DR: It is shown that as embryonic cleavage continues, the amount of amplified rDNA decreases until it is no longer detectable in the early gastrula embryo, and it is concluded that the precursor rRNA sequences synthesized in the oocyte are neither processed nor degraded during early development.
Journal Article•
TL;DR: Classical electron-microscopic techniques allied with autoradiographic studies after [3H]uridine incorporation or after RNA synthesis initiated by an exogeneous RNA polymerase in the presence of tritiated GTP, enabled us to describe the fine structure and activity of the nucleolus in an established Drosophila cell line.
Abstract: Classical electron-microscopic techniques (enzymic digestion, EDTA regressive staining) allied with autoradiographic studies after [3H]uridine incorporation or after RNA synthesis initiated by an exogeneous RNA polymerase in the presence of tritiated GTP, enabled us to describe the fine structure and activity of the nucleolus in an established Drosophila cell line. This nucleolus is composed of a large central multilobed core containing proteins, RNA molecules and a DNA-containing component. This core is surrounded by and connected to large clumps of dense fibrillar nucleolus-associated chromatin, which are intermingled with fibrillogranular ramifications extending from the core towards the nuclear envelope. These ramifications are covered by granules of ribosomal ribonucleoprotein. As shown by EDTA regressive staining the nucleolar core contains a ribonucleoprotein network, which unravels and ramifies within a fibrous matrix. RNA synthesis takes place at the level of this network in the internal part of the core. The molecules synthesized are associated with proteins and are exported out of the core in the form of granules. Although it is composed of the same constituents as other nucleoli, the nucleolus of Drosophila cells seems to be less organized, in that it never displays fibrillar centres, which have been referred to as the nucleolar counterparts of the nucleolus-organizers in a wide variety of organisms.
TL;DR: It is suggested that the VMH experiences a neuronal depopulation in diabetic hamsters which may have a functional influence on the hypothalamic-pancreatic axis in this species.
Abstract: The relationship between diabetes and the size, density and area of the ventromedial hypothalamic nucleus (VMH) was studied in the genetically diabetic Chinese hamster. Matched diabetic and non-diabetic control chinese hamsters were perfused, the hypothalamus collected, sectioned and stained for light microscopy. The mid-point of each VMH nucleus was located, photographed and enlarged for morphometric analysis. Each neuron that possessed a nucleolus and was located within the confines of a VMH was counted, and subsequently the area of each nucleus and the density of neurons per area of VMH were calculated. The results indicated that both the area and absolute number of neurons within the VMH of diabetic hamsters were significantly reduced compared to control values (P<0.01). The density of neurons per unit area of VMH was similar in both groups. These data suggest that the VMH experiences a neuronal depopulation in diabetic hamsters which may have a functional influence on the hypothalamic-pancreatic axis in this species.
TL;DR: Analysis of nucleoproteins in resting human embryonic fibroblasts in vitro at different population doubling levels (PDL) using electron microscopy revealed the disappearance of non-nucleolar ribonucleoprotein structures at high PDL, the nucleoli became larger and the filamentous masses containing the nascent nucleolar RNA displayed a fibrillo-granular pattern which has never been described previously.
TL;DR: It is concluded that all the 45S pre-rRNA molecules synthesized are processed and transferred as 28S and 18S rRNA in the cytoplasm, i.e. degradation (wastage) of newly synthesized ribosomes in the nucleus does not occur in both normal and regenerating rat liver.
Abstract: Kinetic experiments of labelling in vivo with [14C]orotate of cellular free UMP and/or UTP, nucleolar, nucleoplasmic and cytoplasmic rRNA in normal and 12 h-regenerating rat liver were performed. The specific-radioactivity curves obtained were analysed by computer and the rates of synthesis of precursor rRNA (45S pre-rRNA) and cytoplasmic 28S and 18S rRNA calculated. (a) The rates of synthesis of 45S pre-rRNA in normal and regenerating rat liver are 1400 and 3700 molecules/min per nucleus respectively; (b) the average rates of formation of mature 28S and 18S rRNA are identical with the rates of synthesis of 45S pre-rRNA in both normal and regenerating rat liver. Thus the synthesis of rRNA in 12h-regenerating rat liver is activated 2.7-fold. The analysis of rRNA synthesis in isolated nucleoli also shows a 2.7-fold stimulation of transcription in regenerating liver. It is concluded that all the 45S pre-rRNA molecules synthesized are processed and transferred as 28S and 18S rRNA in the cytoplasm, i.e. degradation (wastage) of newly synthesized ribosomes in the nucleus does not occur in both normal and regenerating rat liver. Thus the enhanced production of ribosomes in regenerating rat liver is regulated only at the transcriptional level.
TL;DR: An endoribonuclease which cleaves only single-stranded RNA has been purified from nucleoli of Ehrlich ascites tumor cells, and the enzyme makes endonucleolytic cleavages which generate 5'-phosphate-terminated oligonucleotides.
TL;DR: It is concluded that the autosomal rDNA sequences are inactive in salivary glands and supply additional evidence in favour of a transcriptional inactivity of ribosomal genes with an IVS in Drosophila.
Abstract: The locations of nucleolus organizer regions in the genomes of D. neohydei, D. eohydei and D. repleta were studied by in situ hybridization. All three species carry one nucleolus organizer in the X heterochromatin. The Y chromosomes of D. neohydei and D. eohydei carry two nucleolus organizers in terminal positions comparable to those of D. hydei. The Y chromosome of D. repleta appears also to carry two nucleolus organizer regions, but this is difficult to establish because of the small size of this chromosome. In situ hybridization of ribosomal RNA with salivary gland chromosomes revealed the presence of additional ribosomal DNA sequence clusters in autosomes 2, 3 and 4 of D. neohydei. They form no nucleolus in salivary glands nor are they associated with the nucleolus originating from the sex chromosomal nucleolus organizers. After in vitro pulse-labelling salivary glands with radioactive RNA precursors, no autoradiographic label is associated with the autosomal ribosomal RNA genes. Transcript in situ hybridization gives no label in these autosomal loci. We conclude therefore that the autosomal rDNA sequences are inactive in salivary glands. In situ hybridization with clones of a major part of the 28S intervening sequence (IVS) of D. hydei to polytene chromosomes of D. neohydei results in intense hybridization of the 28S IVS fragment to the autosomal ribosomal DNA sequences. It is therefore suspected that most if not all of the rDNA copies in the autosomes contain an IVS. The inactivity of these ribosomal genes might be the consequence of the presence of intervening sequences in the 28S gene. These observation supply additional evidence in favour of a transcriptional inactivity of ribosomal genes with an IVS in Drosophila. Additional loci with IVS sequences are found in different positions of the genome which do not hybridize with rDNA sequences without IVS.
TL;DR: Evidence was found for the movement and fusion of organizer flanking regions during growth at 35 ° C and the number of junctions between chromatin and nucleolar organizers drops by about half giving one per organizer after segregation, an arrangement suggestive of incipient fusion.
Abstract: Serial sectioning of wheat roots prepared for electron microscopy was used to count the number of fibrillar centres per nucleus and nucleolus and to calculate their sizes. After growth at 35 ° C for two days the nucleoli became segregated and a one to one relationship was evident between chromosomal nucleolar organizers and fibrillar centres. This was confirmed using an aneuploid line carrying an additional pair of organizers. Quantitative studies showed that the fibrillar centres occupied a volume 0.24% of the total chromatin reticulum. From this it was calculated that only about 1/3 of the fibrillar centre material was likely to be nucleolar organizer chromatin. The other material was considered to be the protein revealed in silver staining studies. The importance of this was shown by its constant ratio to the size of all nucleoli in a given nucleus. — Evidence was found for the movement and fusion of organizer flanking regions during growth at 35 ° C. The number of junctions between chromatin and nucleolar organizers drops by about half giving one per organizer after segregation, and serial sectioning demonstrated such junctions in close proximity, an arrangement suggestive of incipient fusion.
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TL;DR: The localization of DNA and RNA synthesis at the various stages of meiosis is discussed in relation to current concepts of chromosome pairing, crossing-over, ribosomal DNA amplification and cycles of RNA metabolism.
Abstract: In an electron microscopic autoradiographic study of DNA and RNA synthesis during meiosis isolated Lilium microsporocytes were supplied with [3H]thymidine and [3H]uridine. DNA synthesis occurred in the nucleus during the zygotene and pachytene intervals of meiotic prophase. Most of the activity was associated with the chromatin, but some synthesis early in zygotene was located at the nucleolus. RNA synthesis occurred throughout prophase until diplotene, when all activity ceased until after division. The newly synthesized RNA was found mostly in association with the chromosomal peripheries or in the space between chromosomes. There was also a peak of [3H]uridine incorporation at the nucleolus, which followed shortly after the synthesis of DNA at that site. The localization of DNA and RNA synthesis at the various stages of meiosis is discussed in relation to current concepts of chromosome pairing, crossing-over, ribosomal DNA amplification and cycles of RNA metabolism.
TL;DR: It is suggested that this persistently labeled RNA represents maternal RNA stored for use during early embryonic development that is incorporated into mouse oocytes during the growth stages.
Abstract: Oocyte development in several nonmammalian species is characterized by the synthesis of large quantities of ribonucleic acids during lampbrush stages of meiosis. These are stored in the oocyte and used during later oocyte maturation and early embryogenesis. This autoradiographic study examined the incorporation and persistence of ribonucleic acid in mouse oocytes during comparable stages of development. At each age examined, fetal through juvenile, the radiolabeled RNA precursors were incorporated into mouse oocytes during the growth stages. The RNAase-digestible label appeared first over nucleoli and meiotic chromosomes, becoming cytoplasmic after 24 hours, and remaining cytoplasmic through all remaining stages. Once incorporated the label persisted during subsequent oocyte growth and maturation through preimplantation embryo stages with apparently undiminished levels. It is suggested that this persistently labeled RNA represents maternal RNA stored for use during early embryonic development.