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Joseph G Gall

Publications and source records attributed to Joseph G Gall.

15 recordsLinked to original sources
PubMed2006

The Drosophila melanogaster Cajal body.

Cajal bodies (CBs) are nuclear organelles that are usually identified by the marker protein p80-coilin. Because no orthologue of coilin is known in Drosophila melanogaster, we identified D. melanogaster CBs using probes for other components that are relatively diagnostic for CBs in vertebrate cells. U85 small CB-specific RNA, U2 small nuclear RNA, the survival of motor neurons protein, and fibrillarin occur together in a nuclear body that is closely associated with the nucleolus. Based on its similarity to CBs in other organisms, we refer to this structure as the D. melanogaster CB. Surprisingly, the D. melanogaster U7 small nuclear RNP resides in a separate nuclear body, which we call the histone locus body (HLB). The HLB is invariably colocalized with the histone gene locus. Thus, canonical CB components are distributed into at least two nuclear bodies in D. melanogaster. The identification of these nuclear bodies now permits a broad range of questions to be asked about CB structure and function in a genetically tractable organism.

Animals↗
PubMed2006

Nuclear bodies in the Drosophila germinal vesicle.

The germinal vesicle of the Drosophila oocyte is transcriptionally quiescent during the latter part of the first meiotic prophase. Concomitant with silencing of the genome, the nucleolus disappears at an early stage and the chromatin condenses into a compact mass called the karyosome. A prominent Cajal body (endobody) is present during most of prophase, attached to the karyosome. Components of the U7 small nuclear (sn) RNP reside in a separate body, the histone locus body, which is also attached to the karyosome. The histone locus body is no longer detectable with probes for the U7 snRNP after about stage 5 of oogenesis. Several other nuclear bodies of unknown nature can be detected by phase contrast, differential interference contrast, and electron microscopy.

Animals↗
PubMed2006

Exporting actin.

Explore the source record for details and available documents.

Actins↗
PubMed2005

Subnuclear organelles: new insights into form and function.

The cell nucleus is a complex and highly dynamic environment with many functionally specialized regions of substructure that form and maintain themselves in the absence of membranes. Relatively little is known about the basic physical properties of the nuclear interior or how domains within the nucleus are structurally and functionally organized and interrelated. Here, we summarize recent data that shed light on the structural and functional properties of three prominent subnuclear organelles--nucleoli, Cajal bodies (CBs) and speckles. We discuss how these findings impact our understanding of the guiding principles of nuclear organization and various types of human disease.

Animals↗
PubMed2004

Cajal bodies, nucleoli, and speckles in the Xenopus oocyte nucleus have a low-density, sponge-like structure.

Nuclear organelles, unlike many cytoplasmic organelles, lack investing membranes and are thus in direct contact with the surrounding nucleoplasm. Because the properties of the nucleoplasm and nuclear organelles influence the exchange of molecules from one compartment to another, it is important to understand their physical structure. We studied the density of the nucleoplasm and the density and permeability of nucleoli, Cajal bodies (CBs), and speckles in the Xenopus oocyte nucleus or germinal vesicle (GV). Refractive indices were measured by interferometry within intact GVs isolated in oil. The refractive indices were used to estimate protein concentrations for nucleoplasm (0.106 g/cm3), CBs (0.136 g/cm3), speckles (0.162 g/cm3), and the dense fibrillar region of nucleoli (0.215 g/cm3). We determined similar protein concentrations for nuclear organelles isolated in aqueous media, where they are no longer surrounded by nucleoplasm. To examine the permeability of nuclear organelles, we injected fluorescent dextrans of various molecular masses (3-2000 kDa) into the cytoplasm or directly into the GV and measured the extent to which they penetrated the organelles. Together, the interferometry and dextran penetration data show that organelles in the Xenopus GV have a low-density, sponge-like structure that provides access to macromolecules from the nucleoplasm.

Animals↗
PubMed2004

Structure in the amphibian germinal vesicle.

The germinal vesicle (GV) of Xenopus laevis is an enormous nucleus that contains 18 giant lampbrush chromosomes and thousands of inclusions. The inclusions are primarily of three types: approximately 1500 extrachromosomal nucleoli, 50-100 Cajal bodies, and several thousand B-snurposomes, which correspond to speckles or interchromatin granule clusters in other nuclei. The large size and abundance of the GV organelles, as well as the ease with which they can be studied both in vivo and in vitro, make the GV an ideal object for analysis of nuclear structure and function.

Amphibians↗
PubMed2004

Dynamics of coilin in Cajal bodies of the Xenopus germinal vesicle.

Cajal bodies (CBs) are complex organelles found in the nuclei of a wide variety of organisms, including vertebrates, invertebrates, plants, and yeast. In most cell types CBs are <1 microm in diameter, severely limiting the range of experimental observations that can be made on them. By contrast, CBs in the amphibian oocyte nucleus (also called the germinal vesicle) are 2-10 microm in diameter. We have taken advantage of this large size to carry out kinetic studies on coilin, a protein that is specifically enriched in CBs. We labeled coilin with photoactivatable green fluorescent protein and analyzed the movement of the protein by confocal microscopy in unfixed germinal vesicles isolated in oil. We showed that coilin leaves the CB relatively slowly (minutes rather than seconds) with kinetics similar to earlier measurements on its entrance. We also showed that coilin diffuses very slowly within the CB, consistent with its being in a large macromolecular complex. Finally, we found that the movement of coilin is not directly affected by the transcriptional state of the nucleus or ongoing nucleocytoplasmic exchange. These data on the kinetics of coilin reinforce the conclusion that CB components are in a constant state of flux, consistent with models that postulate an active role for CBs in nuclear physiology.

Animals↗
PubMed2003

Steady-state dynamics of Cajal body components in the Xenopus germinal vesicle.

Cajal bodies (CBs) are evolutionarily conserved nuclear organelles that contain many factors involved in the transcription and processing of RNA. It has been suggested that macromolecular complexes preassemble or undergo maturation within CBs before they function elsewhere in the nucleus. Most such models of CB function predict a continuous flow of molecules between CBs and the nucleoplasm, but there are few data that directly support this view. We used fluorescence recovery after photobleaching (FRAP) on isolated Xenopus oocyte nuclei to measure the steady-state exchange rate between the nucleoplasm and CBs of three fluorescently tagged molecules: U7 small nuclear RNA, coilin, and TATA-binding protein (TBP). In the nucleoplasm, the apparent diffusion coefficients for the three molecules ranged from 0.26 to 0.40 microm2 s-1. However, in CBs, fluorescence recovery was markedly slower than in the nucleoplasm, and there were at least three kinetic components. The recovery rate within CBs was independent of bleach spot diameter and could not be attributed to high CB viscosity or density. We propose that binding to other molecules and possibly assembly into larger complexes are the rate-limiting steps for FRAP of U7, coilin, and TBP inside CBs.

Active Transport, Cell Nucleus↗
PubMed2003

[A role for Cajal bodies in assembly of the nuclear transcription machinery].

Cajal bodies (CBs) are small nuclear organelles that contain the three eukaryotic RNA polymerases and variety of factors involved in transcription and processing of all types of RNA. A number of these factors, as well as subunits of polymerase (pol) II itself, are rapidly and specifically targeted to CBs when injected into the cell. It is suggested that pol I, pol II and pol III transcription and processing complexes are preassembled in the CBs before transport to the sites of transcription on the chromosomes and in the nucleoli.

Active Transport, Cell Nucleus↗
PubMed2002

Heat shock induces mini-Cajal bodies in the Xenopus germinal vesicle.

Cajal bodies are evolutionarily conserved nuclear organelles that are believed to play a central role in assembly of RNA transcription and processing complexes. Although knowledge of Cajal body composition and behavior has greatly expanded in recent years, little is known about the molecules and mechanisms that lead to the formation of these organelles in the nucleus. The Xenopus oocyte nucleus or germinal vesicle is an excellent model system for the study of Cajal bodies, because it is easy to manipulate and it contains 50-100 Cajal bodies with diameters up to 10 microm. In this study we show that numerous mini-Cajal bodies (less than 2 microm in diameter) form in the germinal vesicle after oocytes recover from heat shock. The mechanism for heat shock induction of mini-Cajal bodies is independent of U7 snRNA and does not require transcription or import of newly translated proteins from the cytoplasm. We suggest that Cajal bodies originate by self-organization of preformed components, preferentially on the surface of B-snurposomes.

Animals↗
PubMed2002

RNA polymerase III in Cajal bodies and lampbrush chromosomes of the Xenopus oocyte nucleus.

We used immunofluorescence to study the distribution and targeting of RNA polymerase (pol) III subunits and pol III transcription factors in the Xenopus laevis oocyte nucleus. Antibodies against several of these proteins stained Cajal bodies and approximately 90 specific sites on the lampbrush chromosomes. Some of the chromosomal sites had been identified previously by in situ hybridization as the genes for 5S rRNA. The remaining sites presumably encode tRNAs and other pol III transcripts. Pol III sites were often resolvable as loops similar to the much more abundant pol II loops, but without a matrix detectable by phase contrast or differential interference contrast. This morphology is consistent with the transcription of short repeated sequences. Hemagglutinin-tagged transcripts encoding core subunits and transcription factors were injected into the oocyte cytoplasm, and the distribution of newly translated proteins inside the nucleus was monitored by immunostaining. Cajal bodies were preferentially targeted by these proteins, and in some cases the chromosomal sites were also weakly stained. The existence of pol III subunits and pol III transcription factors in Cajal bodies and their targeting to these organelles are consistent with a model of Cajal bodies as sites for preassembly of the nuclear transcription machinery.

Amanitins↗
PubMedDate not supplied

The distribution of RNA polymerase II largest subunit (RPB1) in the Xenopus germinal vesicle.

We describe the localization of the largest subunit of RNA polymerase II (RPB1) in the oocyte nucleus of Xenopus laevis. A single oocyte nucleus contains 18 lampbrush chromosomes, approximately 1500 extrachromosomal nucleoli, 50-100 Cajal bodies (CBs) and hundreds to thousands of B-snurposomes. CBs contain many factors involved in RNA transcription and processing, whereas B-snurposomes contain a subset of these factors involved in mRNA processing. Immunofluorescent staining demonstrates that most RPB1 is in the nucleoplasm and that the heptapeptide repeat comprising its carboxy-terminal domain (CTD) is not phosphorylated. A minor fraction of RPB1 is associated with the transcription units of the lampbrush chromosomes and is phosphorylated on serines 2 and 5 of the CTD. Another minor fraction occurs in CBs, which react with antibodies against unphosphorylated CTD repeats and repeats phosphorylated on serine 5. Although B-snurposomes are stained by an antibody against phosphorylated RPB1 (mAb H5), we present evidence that this stain is due to cross-reaction with one or more SR proteins. We show that constructs consisting of 15-17 CTD heptapeptide repeats fused to glutathione-S-transferase are targeted rapidly and specifically to CBs but not to B-snurposomes after injection into the nucleus. The staining and targeting data define at least three distinct populations of RPB1 in the GV with different states of phosphorylation. We suggest that CBs play a unique role in RPB1 metabolism, possibly as sites for assembly or modification of transcription complexes.

Animals↗