Histomorphometry and quantification of nucleolar organizer regions in bovine thyroid containing methylthiouracil residues.
(9/367)
In order to study the morphology and morphometry and to characterize and quantify the nucleolar organizer regions (NORs) of bovine thyroids containing methylthiouracil (MTU) residues, five animals were orally treated with a suspension of MTU (5 g/animal/day) for 20 days (group A). This treatment protocol was interrupted 5 days before the the animals were slaughtered. Six animals receiving placebos composed group B. A third group (group C) was composed of normal thyroids obtained from a slaughterhouse. All glands were previously assessed for detection of antithyroid residues by chromatography, and only those glands from MTU-treated animals were positive. Follicles of glands from group A showed wide variation in size and shape. There was a predominance of small follicles covered by multiple layers of columnar cells, sometimes forming papillary projections into the lumen, characterizing severe interfollicular and intrafollicular adenomatosis. Many follicles had vacuolated cells with nuclei showing karyolysis or pyknosis and reduced amounts of a low-density and very excavated colloid. They also showed higher follicular epithelia and larger proportions of their structural components when compared with glands of groups B and C. In the thyroids from group A, the argyrophilic nucleolar organizer region-associated proteins (AgNORs) were greater in number, with small ones scattered all over the nucleus. Although the size of AgNORs in thyroids from groups B and C was variable, these AgNORs were fewer and larger than were those in glands from group A. In conclusion, the MTU induces proliferation and regressive changes in follicular cells, and the AgNOR technique is efficient to distinguish different degrees of thyroid hyperplasia. (+info)
Nodal signaling patterns the organizer.
(10/367)
Spemann's organizer plays an essential role in patterning the vertebrate embryo. During gastrulation, organizer cells involute and form the prechordal plate anteriorly and the notochord more posteriorly. The fate mapping and gene expression analyses in zebrafish presented in this study reveal that this anteroposterior polarity is already initiated in the organizer before gastrulation. Prechordal plate progenitors reside close to the blastoderm margin and express the homeobox gene goosecoid, whereas notochord precursors are located further from the margin and express the homeobox gene floating head. The nodal-related genes cyclops and squint are expressed at the blastoderm margin and are required for prechordal plate and notochord formation. We show that differential activation of the Nodal signaling pathway is essential in establishing anteroposterior pattern in the organizer. First, overexpression of cyclops and squint at different doses leads to the induction of floating head at low doses and the induction of both goosecoid and floating head at higher doses. Second, decreasing Nodal signaling using different concentrations of the antagonist Antivin inhibits goosecoid expression at low doses and blocks expression of both goosecoid and floating head at higher doses. Third, attenuation of Nodal signaling in zygotic mutants for the EGF-CFC gene one-eyed pinhead, an essential cofactor for Nodal signaling, leads to the loss of goosecoid expression and expansion of floating head expression in the organizer. Concomitantly, cells normally fated to become prechordal plate are transformed into notochord progenitors. Finally, activation of Nodal signaling at different times suggests that prechordal plate specification requires sustained Nodal signaling, whereas transient signaling is sufficient for notochord development. Together, these results indicate that differential Nodal signaling patterns the organizer before gastrulation, with the highest level of activity required for anterior fates and lower activity essential for posterior fates. (+info)
Expression of a highly conserved protein, p27BBP, during the progression of human colorectal cancer.
(11/367)
The highly conserved protein p27BBP is a cytoplasmic interactor of integrin beta4 expressed in epithelia. p27BBP is found in two pools: one nuclear pool enriched in the perinucleolar region, and one cytoplasmic pool. Deletion of p27BBP in yeast is lethal as a result of loss of the ribosomal 60S subunit. The aim of this study was to investigate the distribution of p27BBP in gut epithelium and its behavior during progression of human colorectal carcinomas. Results indicated that p27BBP is high in rapidly cycling cells and decreased in villous cells committed to apoptotic cell death. In dysplastic adenomas and carcinomas, p27BBP displayed a large increase of its nucleolar component that was superimposable to argyrophylic nucleolar organizing region-associated proteins and was associated with the nuclear matrix. Western blotting confirmed increased p27BBP in dysplastic adenomas and in carcinomas. In particular, p27BBP increased progressively from adenomas to carcinomas and, in the latter, was related to the tumor stage. The overexpression of p27BBP corresponded to mRNA up-regulation in carcinomas, supporting the idea of transcriptional or post-transcriptional regulation of its expression. Results suggested that p27BBP alterations are an early event in the transition from benign to malignant colorectal phenotypes and provide a novel tool in surgical pathology. (+info)
NOR regions of polychaete worms of the genus Ophryotrocha studied by chromosome banding techniques and FISH.
(12/367)
This article reports the results of cytogenetic analyses carried out on 10 species of polychaete worms belonging to the genus Ophryotrocha (Dorvilleidae). Nucleolar organizer regions (NORs) were characterized by Ag staining, C-banding, CMA3 staining, and ribosomal fluorescent in situ hybridization (rDNA FISH). Extensive intraspecific variation in NOR number and distribution were observed in O. costlowi, O. sp. macrovifera, O. notoglandulata, O.l. labronica, O. l. pacifica (2n = 6), O. p. puerilis, O. diadema (2n = 8), O. hartmanni, O. gracilis (2n = 10). In O. sp. robusta (2n = 10), Ag-NORs were always located on a single chromosome pair. CMA3 staining suggests a possible trend toward a GC-rich rDNA compartmentalization. In O.l. labronica, O. p. puerilis, O. diadema, and O. sp. robusta rDNA FISH shows that Ag and FISH signals coincide. Results from C-banding seem to indicate that the increased genome size (GS) observed in O. sp. macrovifera (0.8 pg) and O. hartmanni (1.16 pg) compared to the base GS value of the genus (0.4 pg) cannot be attributed to variation in the heterochromatin content. (+info)
The pattern of localized chromosomal breakage induced by the restriction endonuclease HaeIII in reconstructed barley karyotypes T-1586 and T-21 was investigated. It was found that nucleolus organizing regions (NORs) of chromosomes 6 and 7 (segments 46 and 38, respectively), containing actively transcribed ribosomal (r)DNA, as well as segments 39 and 47, both containing condensed rDNA repeats, are the most pronounced aberration hot-spots in T-1586. The number of aberrations observed in these segments was three to five times higher than theoretically expected. The intrachromosomal distribution of chromatid aberrations in karyotype T-21, where the NOR-bearing segments in chromosomes 6 and 7 change their position, revealed a substantial difference in the aberration hot-spot behaviour. A position-specific increase in aberration clustering was observed, most pronounced in segments 38 and 47. On the other hand, segment 46 retained its initial sensitivity, while segment 39 in the new position lost its previous status as a mutation hot-spot. The data are indicative of the expressivity of aberration hot-spots generated after treatment with this restriction endonuclease being influenced by their distinct chromosomal location. (+info)
Antagonists of growth hormone-releasing hormone (GH-RH) inhibit IGF-II production and growth of HT-29 human colon cancers.
(14/367)
Insulin-like growth factors (IGFs) I and II are implicated in progression of various tumours including colorectal carcinomas. To interfere with the production of IGFs, we treated male nude mice bearing xenografts of HT-29 human colon cancer with various potent growth hormone-releasing hormone (GH-RH) antagonists. Twice daily injections of antagonist MZ-4-71, 10 microg intraperitoneally or 5 microg subcutaneously (s.c.) resulted in a significant 43-45% inhibition of tumour growth. Longer acting GH-RH antagonists, MZ-5-156 and JV-1-36 given once daily at doses of 20 microg s.c. produced a 43-58% decrease in volume and weight of cancers. Histological analyses of HT-29 cancers demonstrated that both a decreased cell proliferation and an increased apoptosis contributed to tumour inhibition. GH-RH antagonists did not change serum IGF-I or IGF-II levels, but significantly decreased IGF-II concentration and reduced mRNA expression for IGF-II in tumours. In vitro studies showed that HT-29 cells produced and secreted IGF-II into the medium, and addition of MZ-5-156 dose-dependently decreased IGF-II production by about 40% as well as proliferation of HT-29 cells. Our studies demonstrate that GH-RH antagonists inhibit growth of HT-29 human colon cancers in vivo and in vitro. The effect of GH-RH antagonists may be mediated through a reduced production and secretion of IGF-II by cancer cells. (+info)
Chromosome nondisjunction and instabilities in tapetal cells are affected by B chromosomes in maize.
(15/367)
Abnormal mitosis occurs in maize tapetum, producing binucleate cells that later disintegrate, following a pattern of programmed cell death. FISH allowed us to observe chromosome nondisjunction and micronucleus formation in binucleate cells, using DNA probes specific to B chromosomes (B's), knobbed chromosomes, and the chromosome 6 (NOR) of maize. All chromosome types seem to be involved in micronucleus formation, but the B's form more micronuclei than do knobbed chromosomes and knobbed chromosomes form more than do chromosomes without knobs. Micronuclei were more frequent in 1B plants and in a genotype selected for low B transmission rate. Nondisjunction was observed in all types of FISH-labeled chromosomes. In addition, unlabeled bridges and delayed chromatids were observed in the last telophase before binucleate cell formation, suggesting that nondisjunction might occur in all chromosomes of the maize complement. B nondisjunction is known to occur in the second pollen mitosis and in the endosperm, but it was not previously reported in other tissues. This is also a new report of nondisjunction of chromosomes of the normal set (A's) in tapetal cells. Our results support the conclusion that nondisjunction and micronucleus formation are regular events in the process of the tapetal cell death program, but B's strongly increase A chromosome instability. (+info)
Assembly and functional organization of the nucleolus: ultrastructural analysis of Saccharomyces cerevisiae mutants.
(16/367)
Using Saccharomyces cerevisiae strains with genetically modified nucleoli, we show here that changing parameters as critical as the tandem organization of the ribosomal genes and the polymerase transcribing rDNA, although profoundly modifying the position and the shape of the nucleolus, only partially alter its functional subcompartmentation. High-resolution morphology achieved by cryofixation, together with ultrastructural localization of nucleolar proteins and rRNA, reveals that the nucleolar structure, arising upon transcription of rDNA from plasmids by RNA polymerase I, is still divided in functional subcompartments like the wild-type nucleolus. rRNA maturation is restricted to a fibrillar component, reminiscent of the dense fibrillar component in wild-type cells; a granular component is also present, whereas no fibrillar center can be distinguished, which directly links this latter substructure to rDNA chromosomal organization. Although morphologically different, the mininucleoli observed in cells transcribing rDNA with RNA polymerase II also contain a fibrillar subregion of analogous function, in addition to a dense core of unknown nature. Upon repression of rDNA transcription in this strain or in an RNA polymerase I thermosensitive mutant, the nucleolar structure falls apart (in a reversible manner), and nucleolar constituents partially relocate to the nucleoplasm, indicating that rRNA is a primary determinant for the assembly of the nucleolus. (+info)