Nucleolar morphology and rDNA in situ hybridisation in monocytes

Impaired monocyte activation in schizophrenia: ultrastructural abnormalities and increased IL-1β production

Monocyte activation is consistently reported in patients with schizophrenia (SZ). We aimed to study the ultrastructure of monocytes and monocyte production of IL-1β in drug-free patients with SZ and controls. Monocytes from young (18-30 y.o.) healthy and SZ men in relapse were studied. Electron microscopy and morphometry were applied to estimate areas of monocytes, volume density (Vv), areas, and number of organelles. The production IL-1β by monocytes was estimated by the ELISA method. Group differences were examined using ANCOVA. Pearson's correlation coefficients were used to examine the effects of possible confounding variables. Correlation analyses were applied to detect the relationships between the parameters of monocytes measured and between the parameters measured and the IL-1β production. Area of nucleolus, Vv and area of mitochondria and lysosomes, and the number of lysosomes were significantly increased in patients as compared to controls. Area of mitochondria was correlated significantly with Vv and area of lysosomes, and the number of lysosomes was significantly correlated with area of monocyte and Vv of vacuoles only in the control group. The production of IL-1β by monocytes was higher in patients than in controls (p = 0.01) and was correlated with Vv of lysosomes (r = 0.68, p = 0.04) and area of lysosomes (r = 0.78, p = 0.013). The data provide new evidence for over activation of monocytes in SZ and disturbed metabolic relationships between lysosomes, mitochondria, and vacuoles.

Histone deacetylase inhibition improves activation of ribosomal RNA genes and embryonic nucleolar reprogramming in cloned mouse embryos

Our group found that the treatment of embryos with histone deacetylase inhibitors (HDACi), including trichostatin A, Scriptaid, suberoylanilide hydroxamic acid, and oxamflatin, after cloning by somatic cell nuclear transfer (SCNT) resulted in significantly improved efficiency. Although many researchers have investigated the use of HDACi treatment to improve the quality of cloned mouse embryos, the mechanism underlying this treatment has not been completely understood. We believe that the effect of HDACi on embryonic gene activation (EGA) is important for normal development of cloned embryos. In the present study, using highly sensitive fluorescence in situ hybridization (FISH) with probes complementary to mouse rDNA, the effect of Scriptaid on the onset of rRNA synthesis was examined in cloned embryos. In addition, to determine how Scriptaid affects pre-rRNA processing machinery in SCNT embryos with activated rDNA transcription, functional nucleolar formation was analyzed in detail by combined assessment of rRNA synthesis and nucleolar protein allocation in preimplantation embryos. In this experiment, at least part of the rRNA localization by FISH was substituted by 5-bromouridine 5'-triphosphate staining after alpha-amanitin treatment. The results show that in the late 2-cell stage, a number of SCNT embryos initiated transcriptional activation while having one blastomere showing inactivated rRNA transcription and another blastomere showing activated rRNA transcription and despite both nuclei being in interphase. In addition, in some SCNT embryos, the same nuclei contained a mixture of inactively and actively transcribed rRNA, which was rarely observed in intracytoplasmic sperm injection embryos. This asynchronous transcription induced a delay of one cell cycle in SCNT embryo activation of functional nucleoli. Scriptaid can overcome this failure in the timely onset of embryonic gene transcription by activation of rRNA genes and promotion of nucleolar protein allocation during the early phase of EGA.

High Resolution Mapping of Ribosomal DNA in Early Mouse Embryos by Fluorescence In Situ Hybridization1

The nucleolar precursor bodies (NPBs) are numerous discrete entities present in the nuclei of early mammalian embryos, which structurally support active rRNA genes. However, whether all rRNA genes, including those not transcribed, are spatially associated with NPBs, and moreover what is the general arrangement of ribosomal DNA (rDNA) in early mouse embryos, still remain unanswered questions. In our study, we examined the localization of rDNA in transcriptionally silent (one-cell and early two-cell) and transcriptionally active (late two-cell) mouse embryos by highly sensitive fluorescence in situ hybridization with probes complementary to mouse rDNA repeats. The results obtained showed that irrespective of the rDNA transcriptional status, one or more NPBs per nucleus were not structurally associated with rDNA. These observations support the idea that NPBs are heterogeneous in their ability to recruit rRNA genes and thus to participate in reassembly of the mature nucleolus. As in somatic cells, and despite the absence of the characteristic nucleoli, the general arrangement of rRNA genes in early mouse embryos reflected the intensity of rDNA transcription. Ribosomal RNA genes were unequally distributed with respect to repeat putative copy numbers between nucleolar organizing region (NOR)-bearing chromosomes at the first cleavage division, and more strikingly, between sister chromatid NORs of a single nucleolar organizing chromosome. The latter indicates that sister chromatids might harbor various numbers of rRNA gene copies, and that the genes might be unequally distributed between the two blastomeres during the first cleavage mitosis.

Preferential silver reaction of nucleolar regions adjacent to fibrillar centers in ring shaped nucleoli of leukemic lymphocytes

Silver stained proteins (SSPs) characteristic for interphasic nucleolus organizer regions (NORs) associated with fibrillar centers (FCs) and adjacent nucleolar regions of ring shaped nucleoli in leukemic lymphocytes exhibit a different sensitivity to the mild acid extraction including that with HCl. Such extractions permit a preferential visualization of fibrillar centers adjacent regions (FCARs) which are believed to represent sites of the ribosomal RNA (rRNA) transcription. The resistance of SSPs in FCARs to the extraction with HCl seems to be due to their binding to other components present in these regions. The extractibility of SSPs with HCl was influenced by the fixatives used. The largest resistance of SSPs to the extraction with HCl was noted after fixation with glutaraldehyde. In contrast, the largest extractibility of these proteins was observed after fixation with unbuffered formaldehyde.

Association of pKi-67 with satellite DNA of the human genome in early G1 cells

pKi-67 is a nucleolar antigen that provides a specific marker for proliferating cells. It has been shown previously that pKi-67's distribution varies in a cell cycle-dependent manner: it coats all chromosomes during mitosis, accumulates in nuclear foci during G1 phase (type I distribution) and localizes within nucleoli in late G1 S and G2 phase (type II distribution). Although no function has as yet been ascribed to pKi-67, it has been found associated with centromeres in G1. In the present study the distribution pattern of pKi-67 during G1 in human dermal fibroblasts (HDFs) was analysed in more detail. Synchronization experiments show that in very early G1 cells pKi-67 coincides with virtually all satellite regions analysed, i.e. with centromeric (alpha-satellite), telomeric (minisatellite) and heterochromatic blocks (satellite III) on chromosomes 1 and Y (type Ia distribution). In contrast, later in the G1 phase, a smaller fraction of satellite DNA regions are found collocalized with pKi-67 foci (type Ib distribution). When all pKi-67 becomes localized within nucleoli, even fewer satellite regions remain associated with the pKi-67 staining. However, all centromeric and short arm regions of the acrocentric chromosomes, which are in very close proximity to or even contain the rRNA genes, are collocalized with anti-pKi-67 staining throughout the remaining interphase of the cell cycle. Thus, our data demonstrate that during post-mitotic reformation and nucleogenesis there is a progressive decline in the fraction of specific satellite regions of DNA that remain associated with pKi-67. This may be relevant to nucleolar reformation following mitosis.

Analysis of nucleolar transcription and processing domains and pre-rRNA movements by in situ hybridization

We have examined the cytological localization of rRNA synthesis, transport, and processing events within the mammalian cell nucleolus by double-label fluorescent in situ hybridization analysis using probes for small selected segments of pre-rRNA, which have known half-lives. In particular, a probe for an extremely short-lived 5' region that is not found separate of the pre-rRNA identifies nascent transcripts within the nucleolus of an intact active cell, while other characterized probes identify molecules at different stages in the rRNA processing pathway. Through these studies, visualized by confocal and normal light microscopy, we (1) confirm that rDNA transcription occurs in small foci within nucleoli, (2) show that the nascent pre-rRNA transcripts and most likely also the rDNA templates are surprisingly extended in the nucleolus, (3) provide evidence that the 5' end of the nascent rRNA transcript moves more rapidly away from the template DNA than does the 3' end of the newly released transcript, and (4) demonstrate that the various subsequent rRNA processing steps occur sequentially further from the transcription site, with each early processing event taking place in a distinct nucleolar subdomain. These last three points are contrary to the generally accepted paradigms of nucleolar organization and function. Our findings also imply that the nucleolus is considerably more complex than the conventional view, inferred from electron micrographs, of only three kinds of regions - fibrillar centers, dense fibrillar components, and granular components - for the dense fibrillar component evidently consists of several functionally distinct sub-domains that correlate with different steps of ribosome biogenesis.

Nucleolar coefficient and cytochemistry of human blood monocytes

Nucleoli in peripheral blood monocytes represented mostly by micronucleoli were investigated by means of cytochemical procedures for the demonstration of RNA, proteins of silver stained nucleolus organizer region, nucleophosmin, nucleolin and fibrillarin. The values of the nucleolar coefficient (mean number of nucleoli per cell) were influenced by the procedure used for the visualization of nucleoli. The differences in the values of the nucleolar coefficient of monocytes in one and the same person using above mentioned procedures suggested that micronucleoli in blood monocytes represent heterogeneous nuclear structures and only some of them possess both RNA and characteristic nucleolar proteins. Therefore, the procedures used for the visualization of nucleoli must be always taken into consideration when the values of the nucleolar coefficient are evaluated.

The nucleolus

Nucleoli are the sites of biosynthesis of the ribosomal precursors. They contain may copies of the genes for the main rRNAs (18S- and 28 S-rRNA) in the form of tandemly arranged repeats at the chromosomal nucleolar organizer regions (NORs). They also contain the small rRNA (5S-rRNA) that is synthesized outside the nucleolus, specific nucleolar proteins, among them the factors and enzymes necessary for transcription and transcript processing, and the precursor units of the ribosomes. In man as in may vertebrate species, three main components of nucleoli, besides chromatin, can be detected: fibrillar centres (FC), dense fibrillar component (DCF), and granular component (GC). Within a nucleolus the FCs are in many cases situated in its central region. The DFc forms a network of strands surrounding the FCs, but may sometimes reach for out towards the periphery of the nucleolus. The GC is usually situated in the peripheral regions of the nucleolus. In cells with a low level of ribosomal biosynthesis the nucleoli are small, usually with a single FC and little surrounding DFC and GC ("ring-shaped nucleolus"). In active cells the DFC forms a large network enclosing several, sometimes up to hundreds of FCs, and the GC covers a large area in the periphery ("compact nucleoli"). In cells at the onset of a new stimulation, the DFC is very prominent whereas the FCs are few and small, and the GC is also not very extensive ("reticulate nucleoli"). In some special cell types that are very active other arrangements of the structural components are found. In Sertoli cells, for instance, only one nucleolus is found, or occasionally two, each with a single large FC and a distinct area of GC, both areas being engulfed by DFC intermingled with some peripheral GC. Immunocytological and in situ hybridization studies to localize the rRNA genes within the nucleolus have so far led to divergent results. Both fibrillar components, the FCs and the DFC, have been claimed as the most probable candidates. Transcription of rDNA and the subsequent early steps of ribosome biosynthesis are localized in the DFC, whereas later steps (mature rRNA, preribosomes) are localized in the GC. The FCs may also serve as sites for the preparation of the rDNA for transcription, and as a store for certain nucleolar proteins. During mitosis, parts of the nucleolar proteins remain at the NORs. A direct contact between the nucleolus and the nuclear envelope is frequently observed but is not dependent on nucleolar activity.(ABSTRACT TRUNCATED AT 400 WORDS)