Polytene chromosome

About: Polytene chromosome is a research topic. Over the lifetime, 2667 publications have been published within this topic receiving 88255 citations.

Polycomb and polyhomeotic are constituents of a multimeric protein complex in chromatin of Drosophila melanogaster.

Abstract: The polycomb group (Pc-G) genes are responsible for maintaining the repressed state of homeotic genes during development. It has been suggested that the Pc-G exerts its transcriptional control by regulating higher order chromatin structure. In particular, the finding of genetic and molecular similarities to components involved in heterochromatin formation, led to the proposal that homeotic genes are permanently repressed by mechanisms similar to those responsible for heterochromatin compaction. Because of synergistic effects, Pc-G gene products are thought to act in a multimeric complex. Using immunoprecipitation we show that two members of the Pc-G, Polycomb and polyhomeotic, are constituents of a soluble multimeric protein complex. Size fractionation indicates that a large portion of the two proteins are found in a distinct complex of molecular weight 2-5 x 10(6) Da. During embryogenesis the two proteins show the same spatial distribution. In addition, by double-immunofluorescence labelling we can demonstrate that Polycomb and polyhomeotic have exactly the same binding patterns on polytene chromosomes of larval salivary glands. We propose that some Pc-G proteins act in multimeric complexes to compact the chromatin of stably repressed genes like the homeotic regulators.

A conserved family of nuclear phosphoproteins localized to sites of polymerase II transcription.

Abstract: An antibody was identified previously that recognizes sites of polymerase II transcription on lampbrush chromosomes, puffs on polytene chromosomes, and many small granules in the nucleoplasm of all cells tested. This antibody binds a conserved family of phosphorylated polypeptides in vertebrate and invertebrate cells. We developed a method for purifying these proteins that involves differential solubility in MgCl2. We isolated a Drosophila cDNA encoding one of the proteins using information obtained from microsequencing. In vivo expression studies show that this protein is concentrated on sites of polymerase II transcription and that it is highly phosphorylated. The protein shares a high degree of homology with proteins involved in alternative splicing of pre-mRNA suggesting the possibility that this protein plays a role in pre-mRNA splicing.

Related chromosome binding sites for zeste, suppressors of zeste and Polycomb group proteins in Drosophila and their dependence on Enhancer of zeste function.

Abstract: Polycomb group genes are necessary for maintaining homeotic genes repressed in appropriate parts of the body plan Some of these genes, eg Psc, Su(z)2 and E(z), are also modifiers of the zeste-white interaction The products of Psc and Su(z)2 were immunohistochemically detected at 80-90 sites on polytene chromosomes The chromosomal binding sites of these two proteins were compared with those of zeste protein and two other Polycomb group proteins, Polycomb and polyhomeotic The five proteins co-localize at a large number of sites, suggesting that they frequently act together on target genes In larvae carrying a temperature sensitive mutation in another Polycomb group gene, E(z), the Su(z)2 and Psc products become dissociated from chromatin at non-permissive temperatures from most but not all sites, while the binding of the zeste protein is unaffected The polytene chromosomes in these mutant larvae acquire a decondensed appearance, frequently losing characteristic constrictions These results suggest that the binding of at least some Polycomb group proteins requires interactions with other members of the group and, although zeste can bind independently, its repressive effect on white involves the presence of at least some of the Polycomb group proteins

Active chromatin and transcription play a key role in chromosome partitioning into topologically associating domains

Abstract: Recent advances enabled by the Hi-C technique have unraveled many principles of chromosomal folding that were subsequently linked to disease and gene regulation. In particular, Hi-C revealed that chromosomes of animals are organized into topologically associating domains (TADs), evolutionary conserved compact chromatin domains that influence gene expression. Mechanisms that underlie partitioning of the genome into TADs remain poorly understood. To explore principles of TAD folding in Drosophila melanogaster, we performed Hi-C and poly(A)(+) RNA-seq in four cell lines of various origins (S2, Kc167, DmBG3-c2, and OSC). Contrary to previous studies, we find that regions between TADs (i.e., the inter-TADs and TAD boundaries) in Drosophila are only weakly enriched with the insulator protein dCTCF, while another insulator protein Su(Hw) is preferentially present within TADs. However, Drosophila inter-TADs harbor active chromatin and constitutively transcribed (housekeeping) genes. Accordingly, we find that binding of insulator proteins dCTCF and Su(Hw) predicts TAD boundaries much worse than active chromatin marks do. Interestingly, inter-TADs correspond to decompacted inter-bands of polytene chromosomes, whereas TADs mostly correspond to densely packed bands. Collectively, our results suggest that TADs are condensed chromatin domains depleted in active chromatin marks, separated by regions of active chromatin. We propose the mechanism of TAD self-assembly based on the ability of nucleosomes from inactive chromatin to aggregate, and lack of this ability in acetylated nucleosomal arrays. Finally, we test this hypothesis by polymer simulations and find that TAD partitioning may be explained by different modes of inter-nucleosomal interactions for active and inactive chromatin.

Drosophila Inversion Polymorphism

Abstract: Introduction (C.B. Krimbas and Jeffrey R. Powell). Inferring Chromosome Trees from Inversion Data (J. Sourdis and C.B. Krimbas). Inversion Polymorphisms in Drosophila Pseudoobscura and Drosophila Persimilis (J.R. Powell). The Inversion Polymorphism of Drosophila Subobscura (C.B. Krimbas). Chromosomal Variation in Drosophila Robusta Sturtevant (M. Levitan). Inversion Polymorphism in Drosophila Melanogaster (F. Lemeunier and S. Aulard). Inversion in Hawaiian Drosophila (H.L. Carson). Polytene Chromosome Maps for Hawaiian Drosophila (H.L. Carson, J. Tonzetich, and L.T. Teramoto). Cytological Evolution of the Drosophila Repleta Species Group (M. Wasserman).