Chromocenter


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chromocenter

[′krō·mō‚sen·tər]
(cell and molecular biology)
An irregular, densely staining mass of heterochromatin in the chromosomes, with six armlike extensions of euchromatin, in the salivary glands of Drosophila.

Chromocenter

 

the heterochromatic region of a chromosome that retains the tightly spiralized structure of a chromonema between two successive cell divisions in the interphase. When stained with nuclear dyes, the chromocenter appears under the microscope to be a solid body.

The size and number of chromocenters differ in the interphase nuclei of different organisms and in different tissues of the same organism. Large chromocenters are generally formed by grouped regions of the pericentromere, nucleolar, and telomere hetero-chromatin, as well as by sex chromosomes. In some organisms the number of large chromocenters coincides with the number of chromosomes; in others it is smaller, owing to the fusion of chromocenters, or larger. If polyploid nuclei come into being during the differentiation of somatic cells, complex chromocenters may appear owing to the uniting of the chromocenters of homologous and nonhomologous chromosomes. In Drosophila and in some other dipteran insects, a single large chromocenter is formed in cells with giant polytene chromosomes through the uniting of the centromere regions of all the chromosomes.

A given group of chromocenters reflects the number of chromosome regions inactive in ribonucleic acid (RNA) synthesis and, accordingly, the functional characteristics of the nuclei of different types of cells. The functions of the chromocenter have not been adequately clarified. Frequently repeating sequences of deoxyribonucleic acid (DNA) are generally localized in chromocenters formed by pericentromere heterochromatin.

I. I. KIKNADZE

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For the specimen injected with a solution containing 1.7 mL/kg iron oxide (Figure 7(c)), we observed that the lung parenchyma shows preserved alveolar architecture with rare macrophages in the alveolar septa, discreet anisokaryosis, and anisochromia of type II pneumocytes, with rare chromocenters and nucleoli.
Likewise, the two-dimensional areas of chromocenters in sibling ([bar.x] = 754.9, SD = 279.9) and combinational ([bar.x] = 758.7, SD 299.6) types were not significantly different (t = -0.029, d.f.
This is reflected at the cytological level in lower chromocenter numbers with small sizes.
The amount of interphase heterochomatin per nucleus that was estimated based on chromocenter number and relative area of chromocenter, in A.
Relationship of chromocenter number, size, and density to plant biomass.
Location, geographic coordinates and mean chromocenter number previously reported is shown.
The heterochromatin in the interphase nucleus can be visualized as easily discernible heteropycnotic bodies, called chromocenters, which can vary in number and size.
The chromocenters of the nuclei were stained using a fluorescent dye (Hoechst 33258) which displays a high affinity for interphase heterochromatic regions (Latt and Wohlled, 1975).
The interphase nuclei from nauplii cells, which display the chromocenters observed in the 12 populations studied, are shown in Figure 1.
Analysis of the interphase heterochromatin in Artemia has been based mostly on counting the number of chromocenters using visual methods.