Mitotic recombination in the heterochromatin of the sex chromosomes of Drosophila melanogaster.
(1/1803)
The frequency of spontaneous and X-ray-induced mitotic recombination involving the Y chromosome has been studied in individuals with a marked Y chromosome arm and different XY compound chromosomes. The genotypes used include X chromosomes with different amounts of X heterochromatin and either or both arms of the Y chromosome attached to either side of the centromere. Individuals with two Y chromosomes have also been studied. The results show that the bulk of mitotic recombination takes place between homologous regions. (+info)
Dynamic repositioning of genes in the nucleus of lymphocytes preparing for cell division.
(2/1803)
We show that several transcriptionally inactive genes localize to centromeric heterochromatin in the nucleus of cycling but not quiescent (noncycling) primary B lymphocytes. In quiescent cells, centromeric repositioning of inactive loci was induced after mitogenic stimulation. A dynamic repositioning of selected genes was also observed in developing T cells. Rag and TdT loci were shown to relocate to centromeric domains following heritable gene silencing in primary CD4+8+ thymocytes, but not in a phenotypically similar cell line in which silencing occurred but was not heritable. Collectively, these data indicate that the spatial organization of genes in cycling and noncycling lymphocytes is different and that locus repositioning may be a feature of heritable gene silencing. (+info)
Polymorphisms for the size of heterochromatic regions allow sex-independent quantification of post-BMT chimerism targeting metaphase and interphase cells.
(3/1803)
BACKGROUND AND OBJECTIVE: Fully quantitative cytological techniques for the analysis of hemopoietic chimerism are very limited and largely restricted to sex-chromosome detection after sex-mismatched bone marrow transplants (BMTs). The aim of the present investigation was to assess the usefulness of autosomal polymorphisms for the size of heterochromatic regions in the identification of donor and recipient cells and therefore in the quantification of the hemopoietic chimerism after sex-matched BMT. DESIGN AND METHODS: Hemopoietic chimerism was followed up in 3 transplanted patients targeting a polymorphism for the size of the pericentromeric heterochromatin (PCH) of chromosome 9, uncovered by restriction endonuclease (RE) in situ digestion (REISD) with the RE Sau3A, to differentiate donor and recipient cells on conventional bone marrow chromosome preparations. RESULTS: The polymorphism for the size of the PCH of chromosome 9 allowed differentiation of donor and recipient cells targeting both metaphase and interphase nuclei. The misidentification error for the polymorphism for the size of HPC of chromosome 9 was estimated as 1% for metaphases and 6-11% for interphases. The 3 cases studied showed complete chimerism in the first post-BMT sample analyzed, which was maintained in 2 of them. One patient relapsed and showed transient mixed chimerism. One month later, this patient achieved a second complete remission, showing complete chimerism again. In this patient, who received a sex-mismatched BMT, chimerism was also quantified by sex-chromosome identification using established methods, such as conventional cytogenetics and FISH, and the results obtained were similar to those rendered by Sau3A-REISD. INTERPRETATION AND CONCLUSIONS: The polymorphism for the size of the PCH of chromosome 9 uncovered by Sau3A-REISD allows accurate quantification of the hemopoietic chimerism after sex-matched BMT. (+info)
The relationship between DNA methylation and chromosome imprinting in the coccid Planococcus citri.
(4/1803)
The phenomenon of chromosome, or genomic, imprinting indicates the relevance of parental origin in determining functional differences between alleles, homologous chromosomes, or haploid sets. In mealybug males (Homoptera, Coccoidea), the haploid set of paternal origin undergoes heterochromatization at midcleavage and remains so in most of the tissues. This different behavior of the two haploid sets, which depends on their parental origin, represents one of the most striking examples of chromosome imprinting. In mammals, DNA methylation has been postulated as a possible molecular mechanism to differentially imprint DNA sequences during spermatogenesis or oogenesis. In the present article we addressed the role of DNA methylation in the imprinting of whole haploid sets as it occurs in Coccids. We investigated the DNA methylation patterns at both the molecular and chromosomal level in the mealybug Planococcus citri. We found that in both males and females the paternally derived haploid set is hypomethylated with respect to the maternally derived one. Therefore, in males, it is the paternally derived hypomethylated haploid set that is heterochromatized. Our data suggest that the two haploid sets are imprinted by parent-of-origin-specific DNA methylation with no correlation with the known gene-silencing properties of this base modification. (+info)
Functional mammalian homologues of the Drosophila PEV-modifier Su(var)3-9 encode centromere-associated proteins which complex with the heterochromatin component M31.
(5/1803)
The chromo and SET domains are conserved sequence motifs present in chromosomal proteins that function in epigenetic control of gene expression, presumably by modulating higher order chromatin. Based on sequence information from the SET domain, we have isolated human (SUV39H1) and mouse (Suv39h1) homologues of the dominant Drosophila modifier of position-effect-variegation (PEV) Su(var)3-9. Mammalian homologues contain, in addition to the SET domain, the characteristic chromo domain, a combination that is also preserved in the Schizosaccharyomyces pombe silencing factor clr4. Chromatin-dependent gene regulation is demonstrated by the potential of human SUV39H1 to increase repression of the pericentromeric white marker gene in transgenic flies. Immunodetection of endogenous Suv39h1/SUV39H1 proteins in a variety of mammalian cell lines reveals enriched distribution at heterochromatic foci during interphase and centromere-specific localization during metaphase. In addition, Suv39h1/SUV39H1 proteins associate with M31, currently the only other characterized mammalian SU(VAR) homologue. These data indicate the existence of a mammalian SU(VAR) complex and define Suv39h1/SUV39H1 as novel components of mammalian higher order chromatin. (+info)
UASrpg can function as a heterochromatin boundary element in yeast.
(6/1803)
The HM loci in Saccharomyces cerevisiae constitute region-specific but gene-nonspecific repression domains, as a number of heterologous genes transcribed by RNA polymerase II or III are silenced when placed at these loci. The promoters of the Ashbya gossypii TEF gene and the S. cerevisiae TEF1 and TEF2 genes, however, are resistant to transcriptional silencing by the HM silencers in yeast. Moreover, when interposed between the HML alpha genes and the E silencer, certain segments of these promoters block the repression effect of the silencer on the alpha genes. All of these fragments contain UASrpg (upstream activation sequence of ribosome protein genes) composed of multiple binding sites for Rap1. In fact, a 149-bp segment consisting essentially of only three tandem Rap1-binding sites from the UASrpg of yeast TEF2 exhibits silencer-blocking activity. This element also exhibits insulating activity and orientation dependence characteristic of known chromatin boundary elements. Finally, the element blocks the physical spread of heterochromatin initiated at a silencer. This segment provides the first example of chromatin domain boundary or insulator elements in yeast. (+info)
Phosphorylation of heterochromatin protein 1 by casein kinase II is required for efficient heterochromatin binding in Drosophila.
(7/1803)
Heterochromatin-associated protein 1 (HP1) is a nonhistone chromosomal protein with a dose-dependent effect on heterochromatin mediated position-effect silencing. It is multiply phosphorylated in vivo. Hyperphosphorylation of HP1 is correlated with heterochromatin assembly. We report here that HP1 is phosphorylated by casein kinase II in vivo at three serine residues located at the N and C termini of the protein. Alanine substitution mutations in the casein kinase II target phosphorylation sites dramatically reduce the heterochromatin binding activity of HP1, whereas glutamate substitution mutations, which mimic the charge contributions of phosphorylated serine, have apparently wild-type binding activity. We propose that phosphorylation of HP1 promotes protein-protein interaction between HP1 and target binding proteins in heterochromatin. (+info)
KAP-1 corepressor protein interacts and colocalizes with heterochromatic and euchromatic HP1 proteins: a potential role for Kruppel-associated box-zinc finger proteins in heterochromatin-mediated gene silencing.
(8/1803)
Kruppel-associated box (KRAB) domains are present in approximately one-third of all human zinc finger proteins (ZFPs) and are potent transcriptional repression modules. We have previously cloned a corepressor for the KRAB domain, KAP-1, which is required for KRAB-mediated repression in vivo. To characterize the repression mechanism utilized by KAP-1, we have analyzed the ability of KAP-1 to interact with murine (M31 and M32) and human (HP1alpha and HP1gamma) homologues of the HP1 protein family, a class of nonhistone heterochromatin-associated proteins with a well-established epigenetic gene silencing function in Drosophila. In vitro studies confirmed that KAP-1 is capable of directly interacting with M31 and hHP1alpha, which are normally found in centromeric heterochromatin, as well as M32 and hHP1gamma, both of which are found in euchromatin. Mapping of the region in KAP-1 required for HP1 interaction showed that amino acid substitutions which abolish HP1 binding in vitro reduce KAP-1 mediated repression in vivo. We observed colocalization of KAP-1 with M31 and M32 in interphase nuclei, lending support to the biochemical evidence that M31 and M32 directly interact with KAP-1. The colocalization of KAP-1 with M31 is sometimes found in subnuclear territories of potential pericentromeric heterochromatin, whereas colocalization of KAP-1 and M32 occurs in punctate euchromatic domains throughout the nucleus. This work suggests a mechanism for the recruitment of HP1-like gene products by the KRAB-ZFP-KAP-1 complex to specific loci within the genome through formation of heterochromatin-like complexes that silence gene activity. We speculate that gene-specific repression may be a consequence of the formation of such complexes, ultimately leading to silenced genes in newly formed heterochromatic chromosomal environments. (+info)