Transcription sites are not correlated with chromosome territories in wheat nuclei - PubMed (original) (raw)

Transcription sites are not correlated with chromosome territories in wheat nuclei

R Abranches et al. J Cell Biol. 1998.

Abstract

We have determined the relationship between overall nuclear architecture, chromosome territories, and transcription sites within the nucleus, using three-dimensional confocal microscopy of well preserved tissue sections of wheat roots. Chromosome territories were visualized by GISH using rye genomic probe in wheat/rye translocation and addition lines. The chromosomes appeared as elongated regions and showed a clear centromere-telomere polarization, with the two visualized chromosomes lying approximately parallel to one another across the nucleus. Labeling with probes to telomeres and centromeres confirmed a striking Rabl configuration in all cells, with a clear clustering of the centromeres, and cell files often maintained a common polarity through several division cycles. Transcription sites were detected by BrUTP incorporation in unfixed tissue sections and revealed a pattern of numerous foci uniformly distributed throughout the nucleoplasm, as well as more intensely labeled foci in the nucleoli. It has been suggested that the gene-rich regions in wheat chromosomes are clustered towards the telomeres. However, we found no indication of a difference in concentration of transcription sites between telomere and centromere poles of the nucleus. Neither could we detect any evidence that the transcription sites were preferentially localized with respect to the chromosome territorial boundaries.

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Figures

Figure 1

Figure 1

Root tissue from wheat 1R addition line, in which a pair of rye chromosomes (1R) is present. The rye chromosomes have been labeled by genomic fluorescence in situ hybridization using a total rye genomic DNA probe. A series of optical sections collected by confocal microscopy is shown. The chromosomes stretch across the nuclei, the two arms next to each other, and the two labeled chromosomes are usually parallel to one another. In some cases, the two arms can be distinguished (arrow). Focal distance between section = 1 μm. Bar, 10 μm.

Figure 2

Figure 2

(a) Wheat root tissue double labeled by fluorescence in situ hybridization with probes to the centromeres (green) and telomeres (red). Projection of five confocal optical sections (focal distance between original sections = 1 μm). (b) Diagram showing the interpretation of the labeling in (a) as the Rabl configuration. The chromosomes must all be parallel to one another, with the centromeres clustered on one side of the nuclear periphery, and the telomeres somewhat more dispersed on the other side of the nuclear periphery. A common (alternating) polarity is often maintained through the lines of cells as in this image. Bar, 10 μm.

Figure 3

Figure 3

Labeling of transcription sites in wheat root tissue by incorporation of BrUTP. A single confocal optical section is shown. (a) BrUTP labeling of several nuclei (red). The nucleolar transcription sites are more strongly labeled than the nucleoplasmic sites, and are overexposed in this image. The nucleoplasmic sites are fairly uniformly distributed throughout the nucleoplasm. There is some variability in the intensity of BrUTP labeling, so that, for example, the upper left nucleus is less strongly labeled, but the pattern of labeling is equivalent to that in the other cells. (b) Corresponding DAPI image (blue). (c) Enlargement of the boxed area in a, showing the correspondence between BrUTP sites and chromatin structure. In some cases transcription foci localize to DAPI-dark regions (e.g., arrows), but this is not universal. Bar, 10 μm.

Figure 4

Figure 4

A single confocal image showing double labeling of transcription sites (red, left panel) and centromeres (green, central panel). The two labels are superimposed in the right panel. There is no indication of a polarized distribution of transcription sites, which appear as dense at the centromeric poles of the nuclei as at the opposite, telomeric poles. Bar, 10 μm.

Figure 5

Figure 5

Double labeling of the wheat 1A/1R translocation line, in which one arm of wheat chromosome 1A is substituted by an arm of rye chromosome 1. BrUTP incorporation is shown in red (left-hand panels), genomic in situ labeling in green (central panels), the two labels superimposed in the right hand panels. Three consecutive confocal sections are shown. The distribution of transcription sites shows no sign of being excluded from the interior of the labeled chromosome territory. In fact two prominent sites are clearly inside the chromosome territory (arrows). Section spacing = 1 μm. Bar, 5 μm.

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