Although bulk chromatin is thought to have limited mobility within the interphase eukaryotic nucleus, directed long-distance chromosome movements are not unknown. Cajal bodies (CBs) are nuclear suborganelles that nonrandomly associate with small nuclear RNA (snRNA) and histone gene loci in human cells during interphase. However, the mechanism responsible for this association is uncertain. In this study, we present an experimental system to probe the dynamic interplay of CBs with a U2 snRNA target gene locus during transcriptional activation in living cells. Simultaneous four-dimensional tracking of CBs and U2 genes reveals that target loci are recruited toward relatively stably positioned CBs by long-range chromosomal motion. In the presence of a dominant-negative mutant of β-actin, the repositioning of activated U2 genes is markedly inhibited. This supports a model in which nuclear actin is required for these rapid, long-range chromosomal movements.

Chromosomal aneuploidies are observed in essentially all sporadic carcinomas. These aneuploidies result in tumor-specific patterns of genomic imbalances that are acquired early during tumorigenesis, continuously selected for and faithfully maintained in cancer cells. Although the paradigm of translocation induced oncogene activation in hematologic malignancies is firmly established, it is not known how genomic imbalances affect chromosome-specific gene expression patterns in particular and how chromosomal aneuploidy dysregulates the genetic equilibrium of cells in general. To model specific chromosomal aneuploidies in cancer cells and dissect the immediate consequences of genomic imbalances on the transcriptome, we generated artificial trisomies in a karyotypically stable diploid yet mismatch repair-deficient, colorectal cancer cell line and in telomerase immortalized, cytogenetically normal human breast epithelial cells using microcell-mediated chromosome transfer. The global consequences on gene expression levels were analyzed using cDNA arrays. Our results show that regardless of chromosome or cell type, chromosomal trisomies result in a significant increase in the average transcriptional activity of the trisomic chromosome. This increase affects the expression of numerous genes on other chromosomes as well. We therefore postulate that the genomic imbalances observed in cancer cells exert their effect through a complex pattern of transcriptional dysregulation.

To identify sequential alterations of the genome, transcriptome, and proteome during colorectal cancer progression, we have analyzed tissue samples from 36 patients, including the complete mucosa-adenoma-carcinoma sequence from 8 patients. Comparative genomic hybridization (CGH) revealed patterns of stage specific, recurrent genomic imbalances. Gene expression analysis on 9K cDNA arrays identified 58 genes differentially expressed between normal mucosa and adenoma, 116 genes between adenoma and carcinoma, and 158 genes between primary carcinoma and liver metastasis (P < 0.001). Parallel analysis of our samples by CGH and expression profiling revealed a direct correlation of chromosomal copy number changes with chromosome-specific average gene expression levels. Protein expression was analyzed by two-dimensional gel electrophoresis and subsequent mass spectrometry. Although there was no direct match of differentially expressed proteins and genes, the majority of them belonged to identical pathways or networks. In conclusion, increasing genomic instability and a recurrent pattern of chromosomal imbalances as well as specific gene and protein expression changes correlate with distinct stages of colorectal cancer progression. Chromosomal aneuploidies directly affect average resident gene expression levels, thereby contributing to a massive deregulation of the cellular transcriptome. The identification of novel genes and proteins might deliver molecular targets for diagnostic and therapeutic interventions.

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Primary ciliary dyskinesia syndrome is characterised by chronic sinusitis, bronchiectasis, and, in 50% of cases, dextrocardia. It is generally believed to be inherited as an autosomal recessive disorder. In this report, we describe a family consisting of a mother and her five male children, the offspring of three different fathers, all of whom have this syndrome. This argues for either an X linked or autosomal dominant pattern of inheritance. Cytogenetic and FISH (fluorescent in situ hybridisation) analyses were done on the mother and one son and were found to be normal.

The azoxymethane (AOM)-induced mouse colon tumor model recapitulates many of the histopathological features associated with the multistage progression of human sporadic colorectal cancers (CRCs). To better define the genetic events associated with tumorigenesis in this murine model, we analysed tumors from A/J mice for chromosomal (CIN) and microsatellite (MSI) instabilities, two fundamental pathways of genomic instability that play a critical role in the pathogenesis of human CRCs. Male A/ J mice, 6-week old, were injected with either AOM (n ¼ 5) (10 mg/kg b.w., i.p.) or vehicle (n ¼ 5) (0.9% NaCl solution) once a week for 6 weeks. At 32 weeks after the last dose, comparative genomic hybridization (CGH) was performed on 16 tumors harvested from five animals. Although 25% of the tumors displayed either a gain of chromosome 2 or loss of Y, the majority (75%) showed no genomic imbalances. Further analysis of chromosomal aberrations, using CGH and spectral karyotyping (SKY) was performed in our recently established A/J colon tumor-derived cell line, AJ02-NM 0 . Results showed a pseudotetraploid karyotype with loss of only the Y chromosome in these cultured cells, thereby providing additional evidence for the minimal role of CIN in the primary AOM-induced tumors. Interestingly, the majority (81%) of A/J tumors displayed low-level microsatellite instability (MSI-L) when analysed using mono-and dinucleotide repeat markers, and showed a significant expansion to high-level instability (MSI-H) in the AJ02-NM 0 cells. This finding in cultured cells additionally provides evidence that a mild mutator pathway may contribute to the development of behaviorally benign carcinomas in situ in A/J mice. To better understand the tumorigenic process in the A/J colons, we screened for mutational alterations in key regions of the K-ras and Apc genes. Results showed a very low frequency (6%) of K-ras activating mutations, together with the absence of Apc truncation mutations in primary tumors and AJ02-NM 0 cells. However, these tumors displayed intense nuclear accumulation of b-catenin protein, indicating activation of the Wnt signaling pathway. Based on our molecular and cytogenetic findings, we propose that carcinogen-induced tumors may develop via mechanisms independent of the 'classical' CIN or MSI pathways.

BackgroundChromosomal aneuploidy is a defining feature of carcinomas. For instance, in colon cancer, an additional copy of Chromosome 7 is not only observed in early pre-malignant polyps, but is faithfully maintained throughout progression to metastasis. These copy number changes show a positive correlation with average transcript levels of resident genes. An independent line of research has also established that specific chromosomes occupy a well conserved 3D position within the interphase nucleus.Methodology/Principal FindingsWe investigated whether cancer-specific aneuploid chromosomes assume a 3D-position similar to that of its endogenous homologues, which would suggest a possible correlation with transcriptional activity. Using 3D-FISH and confocal laser scanning microscopy, we show that Chromosomes 7, 18, or 19 introduced via microcell-mediated chromosome transfer into the parental diploid colon cancer cell line DLD-1 maintain their conserved position in the interphase nucleus.ConclusionsOur data is therefore consistent with the model that each chromosome has an associated zip code (possibly gene density) that determines its nuclear localization. Whether the nuclear localization determines or is determined by the transcriptional activity of resident genes has yet to be ascertained.

Neuronal elimination in the developing CNS is accomplished by an orderly type of cellular suicide called programmed cell death. The principal non-neuronal cells implicated in regulating programmed cell death and subsequent phagocytosis of dying neurons are the brain’s macrophage population, the microglia. Little is known about the signaling between microglia and neurons during programmed cell death. However, macrophages in non-neural tissues express receptors for immunoglobulin (IgG) and complement, and these molecules help regulate phagocytosis of dying cells and foreign organisms. Since many of the neurons generated early in CNS development are transient cell types that are immunoreactive for IgG [Upender et al.: J Comp Neurol 1997; 384:271–282], we hypothesized that IgG might alter the phagocytic properties of microglia within the developing nervous system and potentiate engulfment of dying cells. To begin to address this hypothesis, we first asked whether cortical neurons immunoreactive for IgG or calbindin-D28k exhibit morphological evidence of programmed cell death in the cerebral cortex of neonatal rat pups. Secondly, we quantified the incidence of contacts made by microglia on IgG- vs. calbindin-immunoreactive neurons. Thirdly, perturbation experiments were performed to elevate intracortical levels of IgG and the incidence of microglia:neuron contacts were determined. We found that although the nuclei of some IgG-immunoreactive neurons exhibited condensation and fragmentation characteristic of programmed cell death, we did not observe pyknotic calbindin-immunoreactive neurons. IgG-immunoreactive neurons were also more likely to be contacted by microglia than calbindin-immunoreactive neurons. Elevating intracortical levels of IgG experimentally led to a dramatic increase in the expression of microglia complement receptors throughout the cerebral cortex. Taken together, these results suggest that IgG normally present within neuronal subsets in the developing cerebral cortex could serve to locally regulate the expression of complement receptors on microglia.