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45S rDNA regions are chromosome fragile sites expressed as gaps in vitro on metaphase chromosomes of root-tip meristematic cells in Lolium spp.

Huang J, Ma L, Yang F, Fei SZ, Li L - PLoS ONE (2008)

Bottom Line: During the course of cytological mapping of rDNA on ryegrass chromosomes, we found that the number of chromosomes plus chromosome fragments was often more than the expected 14 in most cells for Lolium perenne L. cv.Top One.The chromosome lesions observed in this study are very similar cytologically to that of fragile sites observed in human chromosomes, and thus we conclude that the high frequency of chromosome lesions in vitro in Lolium species is the result of the expression of 45S rDNA fragile sites.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Ministry of Education for Plant Development Biology, College of Life Sciences, Wuhan University, Wuhan, China.

ABSTRACT

Background: In humans, chromosome fragile sites are regions that are especially prone to forming non-staining gaps, constrictions or breaks in one or both of the chromatids on metaphase chromosomes either spontaneously or following partial inhibition of DNA synthesis and have been well identified. So far, no plant chromosome fragile sites similar to those in human chromosomes have been reported.

Methods and results: During the course of cytological mapping of rDNA on ryegrass chromosomes, we found that the number of chromosomes plus chromosome fragments was often more than the expected 14 in most cells for Lolium perenne L. cv. Player by close cytological examination using a routine chromosome preparation procedure. Further fluorescent in situ hybridization (FISH) using 45S rDNA as a probe indicated that the root-tip cells having more than a 14-chromosome plus chromosome fragment count were a result of chromosome breakage or gap formation in vitro (referred to as chromosome lesions) at 45S rDNA sites, and 86% of the cells exhibited chromosome breaks or gaps and all occurred at the sites of 45S rDNA in Lolium perenne L. cv. Player, as well as in L. multiflorum Lam. cv. Top One. Chromatin depletion or decondensation occurred at various locations within the 45S rDNA regions, suggesting heterogeneity of lesions of 45S rDNA sites with respect to their position within the rDNA region.

Conclusions: The chromosome lesions observed in this study are very similar cytologically to that of fragile sites observed in human chromosomes, and thus we conclude that the high frequency of chromosome lesions in vitro in Lolium species is the result of the expression of 45S rDNA fragile sites. Possible causes for the spontaneous expression of fragile sites and their potential biological significance are discussed.

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Related in: MedlinePlus

a: Varied chromosome plus chromosome fragment count of mitotic chromosomes in vitro in the diploid Lolium perenne cv. Player (2n = 14) due to chromosome lesions.Figs A–F show the variation of chromosome plus chromosome fragment numbers from 15 to 20 in different metaphase cells. A: 15, B: 16, C: 17, D: 18, E: 19, F: 20. b: The pie chart represents the percentages of cells with different chromosome plus chromosome fragment counts. Bar = 5 µm.
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pone-0002167-g001: a: Varied chromosome plus chromosome fragment count of mitotic chromosomes in vitro in the diploid Lolium perenne cv. Player (2n = 14) due to chromosome lesions.Figs A–F show the variation of chromosome plus chromosome fragment numbers from 15 to 20 in different metaphase cells. A: 15, B: 16, C: 17, D: 18, E: 19, F: 20. b: The pie chart represents the percentages of cells with different chromosome plus chromosome fragment counts. Bar = 5 µm.

Mentions: During the course of cytological mapping of rDNA on ryegrass chromosomes, we found that the number of chromosomes plus chromosome fragments was often more than the expected 14 in most cells for Lolium perenne L. cv. Player by close cytological examination using a routine chromosome preparation procedure (Figure 1a). However, it is difficult to distinguish whether one “chromosome” is a complete chromosome or merely a chromosome fragment before mapping 45S rDNA by FISH. The frequency of chromosome lesions in vitro was quite high. In the 119 metaphase cells analyzed, there were only 18 cells with the normal 14 chromosomes (15%), while the number of cells with 15, 16, 17, 18, 19 or 20 chromosomes plus chromosome fragments accounted for the majority of cells (85%, Figure 1b).


45S rDNA regions are chromosome fragile sites expressed as gaps in vitro on metaphase chromosomes of root-tip meristematic cells in Lolium spp.

Huang J, Ma L, Yang F, Fei SZ, Li L - PLoS ONE (2008)

a: Varied chromosome plus chromosome fragment count of mitotic chromosomes in vitro in the diploid Lolium perenne cv. Player (2n = 14) due to chromosome lesions.Figs A–F show the variation of chromosome plus chromosome fragment numbers from 15 to 20 in different metaphase cells. A: 15, B: 16, C: 17, D: 18, E: 19, F: 20. b: The pie chart represents the percentages of cells with different chromosome plus chromosome fragment counts. Bar = 5 µm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2366065&req=5

pone-0002167-g001: a: Varied chromosome plus chromosome fragment count of mitotic chromosomes in vitro in the diploid Lolium perenne cv. Player (2n = 14) due to chromosome lesions.Figs A–F show the variation of chromosome plus chromosome fragment numbers from 15 to 20 in different metaphase cells. A: 15, B: 16, C: 17, D: 18, E: 19, F: 20. b: The pie chart represents the percentages of cells with different chromosome plus chromosome fragment counts. Bar = 5 µm.
Mentions: During the course of cytological mapping of rDNA on ryegrass chromosomes, we found that the number of chromosomes plus chromosome fragments was often more than the expected 14 in most cells for Lolium perenne L. cv. Player by close cytological examination using a routine chromosome preparation procedure (Figure 1a). However, it is difficult to distinguish whether one “chromosome” is a complete chromosome or merely a chromosome fragment before mapping 45S rDNA by FISH. The frequency of chromosome lesions in vitro was quite high. In the 119 metaphase cells analyzed, there were only 18 cells with the normal 14 chromosomes (15%), while the number of cells with 15, 16, 17, 18, 19 or 20 chromosomes plus chromosome fragments accounted for the majority of cells (85%, Figure 1b).

Bottom Line: During the course of cytological mapping of rDNA on ryegrass chromosomes, we found that the number of chromosomes plus chromosome fragments was often more than the expected 14 in most cells for Lolium perenne L. cv.Top One.The chromosome lesions observed in this study are very similar cytologically to that of fragile sites observed in human chromosomes, and thus we conclude that the high frequency of chromosome lesions in vitro in Lolium species is the result of the expression of 45S rDNA fragile sites.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Ministry of Education for Plant Development Biology, College of Life Sciences, Wuhan University, Wuhan, China.

ABSTRACT

Background: In humans, chromosome fragile sites are regions that are especially prone to forming non-staining gaps, constrictions or breaks in one or both of the chromatids on metaphase chromosomes either spontaneously or following partial inhibition of DNA synthesis and have been well identified. So far, no plant chromosome fragile sites similar to those in human chromosomes have been reported.

Methods and results: During the course of cytological mapping of rDNA on ryegrass chromosomes, we found that the number of chromosomes plus chromosome fragments was often more than the expected 14 in most cells for Lolium perenne L. cv. Player by close cytological examination using a routine chromosome preparation procedure. Further fluorescent in situ hybridization (FISH) using 45S rDNA as a probe indicated that the root-tip cells having more than a 14-chromosome plus chromosome fragment count were a result of chromosome breakage or gap formation in vitro (referred to as chromosome lesions) at 45S rDNA sites, and 86% of the cells exhibited chromosome breaks or gaps and all occurred at the sites of 45S rDNA in Lolium perenne L. cv. Player, as well as in L. multiflorum Lam. cv. Top One. Chromatin depletion or decondensation occurred at various locations within the 45S rDNA regions, suggesting heterogeneity of lesions of 45S rDNA sites with respect to their position within the rDNA region.

Conclusions: The chromosome lesions observed in this study are very similar cytologically to that of fragile sites observed in human chromosomes, and thus we conclude that the high frequency of chromosome lesions in vitro in Lolium species is the result of the expression of 45S rDNA fragile sites. Possible causes for the spontaneous expression of fragile sites and their potential biological significance are discussed.

Show MeSH
Related in: MedlinePlus