Organization Of Polytene Chromosomes Research Articles

Study of the organization of polytene chromosomes in the nuclei of Drosophila melanogaster pseudonurse cells with the use of the DNA library of the Drosophila orena chromocenter

The location of the Drosophila orena chromocenter in polytene chromosomes of pseudonurse cells of the D. melanogaster ovaries (the otu11 mutation) and salivary glands has been studied. Numerous sites of location of the D. orena chromocenter DNA have been found throughout the length of D. melanogaster chromosomes. The specific distribution of the binding sites for the DNA probe has made it possible to identify chromosomes and analyze their mutual positions in the three-dimensional space of the nuclei of pseudonurse cells. The mutual positions of chromosomes have been found to vary, the pericentromeric regions of different chromosomes differing from one another in associative ratios.

An integrated description of polytene chromosome structure

An integrated description from nucleohistone fiber level to light microscopic level of polytene chromosomes is presented. The integration is based on the results obtained by different new applications of electron microscopic techniques and on the analysis of earlier data of chromatin structure. A model for the organization of polytene chromosomes in vivo is extrapolated from the EM-data by approximating the effects of the physico-chemical parameters changing during preparative procedures. The nucleosome unit fiber forms loops, which are organized into about 500A diameter coils with 24 nucleosomes per turn of the double fiber, leading to an overall packing ratio of about 1:78. The coils are packed differentially into structural units forming the polytene bands, which are separated from each other by interbands of unit fibers with no higher order coiling evident. For the general higher order structure of chromatin a model capable of explaining former observations in other eukaryotic chromosome systems is proposed. A whole mount method suitable for nucleosome fiber examination in polytene chromosomes is introduced. A sectioning method preserving the nucleosomal structures and a quick method for whole mounting polytene chromosomes retaining their light microscopic morphology are also described.

Polytene chromosomes from ovarian nurse cells of Drosophila melanogaster otu mutants.

Polytene chromosomes from the salivary gland cells of Drosophila melanogaster larvae have been the most useful model for studying the functional morphology of interphase eukaryotic chromosomes since their discovery almost 70 yr ago (). The question remains as to whether the polytene structure is universal. How similar is the organization of polytene chromosomes in different tissues, because cell differentiation may lead to diverse functional chromosome states? The greatest difference can be expected to be seen between the chromosomes of the germ-line cells and the cells of somatic tissue.

Organization of the Drosophila genome in mutants with changes in second messenger metabolism and learning ability.

Mechanisms modifying the structural-functional organization of polytene chromosomes were studied in a Drosophila line in which the activating properties of calmodulin were altered and learning ability was increased, by treating mutants with homeopathic preparations which affect Ca2+ and F- ion metabolism. The results indicated a dominant role for Ca2+ ions and calmodulin in determining the chromocentric organization of the nucleus. F- ions, which stimulate the adenylate cyclase complex, were found not to have a role.

Molecular cytogenetic organization of polytene chromosomes

The results of the works carried out in the Laboratory of Molecular Cytogenetics (Institute of Cytology and Genetics of Siberian Branch of the RAS, Novosibirsk) devoted to the molecular genetic analysis of main units of polytene chromosomes, bands, interbands, and puffs, as well as intercalary and pericentric heterochromatin, are summarized. The results are discussed in terms of the dynamic model of organization of polytene chromosomes.

RNA synthesis in the embryo suspensor ofPhaseolus coccineus at two stages of embryogenesis, and the effect of supplied gibberellic acid

RNA synthesis in giant cells containing polytene chromosomes in the embryo suspensor ofPhaseolus coccineus was analyzed by autoradiography after [3H]-uridine treatment. Embryos at the heart-shaped stage of development and at a cotyledonary stage were studied. Discontinuous labelling of the polytene chromosomes was always observed. The chromosomes were subdivided into segments (chromosome regions) which behaved as functional units, since discontinuous labelling was never seen within any of the regions. It was found that most chromosome regions were engaged in RNA synthesis to different degrees at the two embryo developmental stages. Regions showing identical labelling patterns tended to lie close together in the chromosome arms and to keep their functional activity coordinated at both stages of embryo development. The chromosome regions bearing 18 S+25 S ribosomal genes were never simultaneously active in RNA synthesis and different regions were preferentially transcribed at each stage of embryo development. However, at both stages, all the chromosome regions bearing 5 S ribosomal genes showed comparable labelling frequencies. The effect on transcription of gibberellic acid (GA3) treatments was also studied. At both embryo developmental stages, GA3 enhanced the rate of RNA synthesis in the polytene suspensor cells. The frequency with which certain chromosome regions were transcribed was also increased significantly (P⩽0.001) and this stimulatory effect was greater in embryos at the cotyledonary stage than in heart-shaped embryos. At the latter developmental stage, RNA synthesis was repressed by GA3 in a few chromosome regions. These results are discussed briefly in relation to previous findings using different methods of studying the organization of polytene chromosomes and the functional activity of the embryo suspensor ofPhaseolus coccineus.

Chromomeric organization of polytene chromosomes

This is a review summarizing work carried out at the Laboratory of Molecular Cytogenetics in recent years. Problems of genetic organization of bands, interbands and puffs as well as intercalary heterochromatin and position effect variegation are discussed from the point of view of the dynamic model of polytene chromosome organization.

Genetic interpretation of polytene chromosomes banding pattern.

This mini-review covers new data regarding the problem of the functional organization of polytene chromosomes: The localization of RNA synthesis in the polytene chromosome puffs, diffuse bands and interbands; The relative stability of banding pattern and its functional value; The informational content of bands.

Functional organization of polytene chromosomes.

Functional organization of polytene chromosomes.