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The C. elegans dosage compensation complex mediates interphase X chromosome compaction.

Lau AC, Nabeshima K, Csankovszki G - Epigenetics Chromatin (2014)

Bottom Line: In addition, we show that SET-1, SET-4, and SIR-2.1, histone modifiers whose activity is regulated by the DCC, need to be present for the compaction of the X chromosome territory.These results support the idea that condensin I(DC), and the histone modifications regulated by the DCC, mediate interphase X chromosome compaction.Our results link condensin-mediated chromosome compaction, an activity connected to mitotic chromosome condensation, to chromosome-wide repression of gene expression in interphase.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109 Michigan.

ABSTRACT

Background: Dosage compensation is a specialized gene regulatory mechanism which equalizes X-linked gene expression between sexes. In Caenorhabditis elegans, dosage compensation is achieved by the activity of the dosage compensation complex (DCC). The DCC localizes to both X chromosomes in hermaphrodites to downregulate gene expression by half. The DCC contains a subcomplex (condensin I(DC)) similar to the evolutionarily conserved condensin complexes which play fundamental roles in chromosome dynamics during mitosis and meiosis. Therefore, mechanisms related to mitotic chromosome condensation have been long hypothesized to mediate dosage compensation. However experimental evidence was lacking.

Results: Using 3D FISH microscopy to measure the volumes of X and chromosome I territories and to measure distances between individual loci, we show that hermaphrodite worms deficient in DCC proteins have enlarged interphase X chromosomes when compared to wild type. By contrast, chromosome I is unaffected. Interestingly, hermaphrodite worms depleted of condensin I or II show no phenotype. Therefore X chromosome compaction is specific to condensin I(DC). In addition, we show that SET-1, SET-4, and SIR-2.1, histone modifiers whose activity is regulated by the DCC, need to be present for the compaction of the X chromosome territory.

Conclusion: These results support the idea that condensin I(DC), and the histone modifications regulated by the DCC, mediate interphase X chromosome compaction. Our results link condensin-mediated chromosome compaction, an activity connected to mitotic chromosome condensation, to chromosome-wide repression of gene expression in interphase.

No MeSH data available.


Related in: MedlinePlus

The decondensed X chromatin structure in DCC-depleted worms is a result of defective compaction. (A, B) Adult RNAi treated hermaphrodite diploid nuclei stained with X-paint FISH (red) to label X chromosome territories and DAPI (blue) to label DNA. (A) Representative stained nuclei after vector RNAi treatment, dpy-30(RNAi), dpy-21(RNAi), and dpy-27(RNAi). Scale bars equal 5 μm. (B) Quantification of the percentage of nuclear volume occupied by X in vector RNAi (n = 40), dpy-30(RNAi) (n = 40), dpy-21(RNAi) (n = 40), and dpy-27(RNAi) (n = 40). Error bars indicate standard deviation. Asterisks indicate level of statistical significance by t-test analysis (three asterisks, P <0.001). (C, D) Adult hermaphrodite diploid nuclei stained with chromosome I paint FISH (red) to label chromosome I territories and DAPI (blue) to label DNA after DCC depletion. (C) Representative stained nuclei after vector RNAi treatment, dpy-30(RNAi), dpy-21(RNAi), and dpy-27(RNAi). Scale bars equal 5 μm. (D) Quantification of the percentage of nuclear volume occupied by chromosome I in vector RNAi (n = 40), dpy-30(RNAi) (n = 40), dpy-21(RNAi) (n = 40), and dpy-27(RNAi) (n = 40). Error bars indicate standard deviation.
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Fig3: The decondensed X chromatin structure in DCC-depleted worms is a result of defective compaction. (A, B) Adult RNAi treated hermaphrodite diploid nuclei stained with X-paint FISH (red) to label X chromosome territories and DAPI (blue) to label DNA. (A) Representative stained nuclei after vector RNAi treatment, dpy-30(RNAi), dpy-21(RNAi), and dpy-27(RNAi). Scale bars equal 5 μm. (B) Quantification of the percentage of nuclear volume occupied by X in vector RNAi (n = 40), dpy-30(RNAi) (n = 40), dpy-21(RNAi) (n = 40), and dpy-27(RNAi) (n = 40). Error bars indicate standard deviation. Asterisks indicate level of statistical significance by t-test analysis (three asterisks, P <0.001). (C, D) Adult hermaphrodite diploid nuclei stained with chromosome I paint FISH (red) to label chromosome I territories and DAPI (blue) to label DNA after DCC depletion. (C) Representative stained nuclei after vector RNAi treatment, dpy-30(RNAi), dpy-21(RNAi), and dpy-27(RNAi). Scale bars equal 5 μm. (D) Quantification of the percentage of nuclear volume occupied by chromosome I in vector RNAi (n = 40), dpy-30(RNAi) (n = 40), dpy-21(RNAi) (n = 40), and dpy-27(RNAi) (n = 40). Error bars indicate standard deviation.

Mentions: Because intestinal nuclei are 32-ploid, the possibility remained that the enlarged X territories were a result of the dispersing of the multiple copies of the X chromosomes and not a result of perturbed compaction of individual chromosomes. To test this possibility, we examined the X chromosomes in the diploid tail tip hypodermal cells, hyp 8-11 [55]. We found similar results to that of intestinal nuclei in the diploid cells (Figure 3A and B). The X chromosome territories in vector control RNAi diploid cells were tightly compact occupying 9.94 ± 2.20%, whereas the X chromosome territories in dpy-30, dpy-21, and dpy-27 RNAi diploid cells were decondensed occupying 16.27 ± 2.62% (P = 6.70E-19), 16.09 ± 2.22% (P = 3.02E-20), and 16.17 ± 2.59% (P = 1.15E-18), respectively. Additionally, the percent volume occupied by chromosome I in diploid cells was not statistically different amongst the control and DCC-depleted animals, averaging 13.2% in all cases (Figure 3C and D). This suggests that the decondensed X chromatin structure in DCC-depleted worms is not solely a result of the dispersing of the multiple copies of the X chromosome in the 32-ploid intestinal nuclei, but it is a result of defective compaction. We did not look at separate X chromosome territories in diploid cells because due to their small size only a small percentage of nuclei had clearly distinguishable X chromosome territories. Only 35% of both vector and dpy-27(RNAi) diploid nuclei clearly exhibited two separate X chromosome territories.Figure 3


The C. elegans dosage compensation complex mediates interphase X chromosome compaction.

Lau AC, Nabeshima K, Csankovszki G - Epigenetics Chromatin (2014)

The decondensed X chromatin structure in DCC-depleted worms is a result of defective compaction. (A, B) Adult RNAi treated hermaphrodite diploid nuclei stained with X-paint FISH (red) to label X chromosome territories and DAPI (blue) to label DNA. (A) Representative stained nuclei after vector RNAi treatment, dpy-30(RNAi), dpy-21(RNAi), and dpy-27(RNAi). Scale bars equal 5 μm. (B) Quantification of the percentage of nuclear volume occupied by X in vector RNAi (n = 40), dpy-30(RNAi) (n = 40), dpy-21(RNAi) (n = 40), and dpy-27(RNAi) (n = 40). Error bars indicate standard deviation. Asterisks indicate level of statistical significance by t-test analysis (three asterisks, P <0.001). (C, D) Adult hermaphrodite diploid nuclei stained with chromosome I paint FISH (red) to label chromosome I territories and DAPI (blue) to label DNA after DCC depletion. (C) Representative stained nuclei after vector RNAi treatment, dpy-30(RNAi), dpy-21(RNAi), and dpy-27(RNAi). Scale bars equal 5 μm. (D) Quantification of the percentage of nuclear volume occupied by chromosome I in vector RNAi (n = 40), dpy-30(RNAi) (n = 40), dpy-21(RNAi) (n = 40), and dpy-27(RNAi) (n = 40). Error bars indicate standard deviation.
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Fig3: The decondensed X chromatin structure in DCC-depleted worms is a result of defective compaction. (A, B) Adult RNAi treated hermaphrodite diploid nuclei stained with X-paint FISH (red) to label X chromosome territories and DAPI (blue) to label DNA. (A) Representative stained nuclei after vector RNAi treatment, dpy-30(RNAi), dpy-21(RNAi), and dpy-27(RNAi). Scale bars equal 5 μm. (B) Quantification of the percentage of nuclear volume occupied by X in vector RNAi (n = 40), dpy-30(RNAi) (n = 40), dpy-21(RNAi) (n = 40), and dpy-27(RNAi) (n = 40). Error bars indicate standard deviation. Asterisks indicate level of statistical significance by t-test analysis (three asterisks, P <0.001). (C, D) Adult hermaphrodite diploid nuclei stained with chromosome I paint FISH (red) to label chromosome I territories and DAPI (blue) to label DNA after DCC depletion. (C) Representative stained nuclei after vector RNAi treatment, dpy-30(RNAi), dpy-21(RNAi), and dpy-27(RNAi). Scale bars equal 5 μm. (D) Quantification of the percentage of nuclear volume occupied by chromosome I in vector RNAi (n = 40), dpy-30(RNAi) (n = 40), dpy-21(RNAi) (n = 40), and dpy-27(RNAi) (n = 40). Error bars indicate standard deviation.
Mentions: Because intestinal nuclei are 32-ploid, the possibility remained that the enlarged X territories were a result of the dispersing of the multiple copies of the X chromosomes and not a result of perturbed compaction of individual chromosomes. To test this possibility, we examined the X chromosomes in the diploid tail tip hypodermal cells, hyp 8-11 [55]. We found similar results to that of intestinal nuclei in the diploid cells (Figure 3A and B). The X chromosome territories in vector control RNAi diploid cells were tightly compact occupying 9.94 ± 2.20%, whereas the X chromosome territories in dpy-30, dpy-21, and dpy-27 RNAi diploid cells were decondensed occupying 16.27 ± 2.62% (P = 6.70E-19), 16.09 ± 2.22% (P = 3.02E-20), and 16.17 ± 2.59% (P = 1.15E-18), respectively. Additionally, the percent volume occupied by chromosome I in diploid cells was not statistically different amongst the control and DCC-depleted animals, averaging 13.2% in all cases (Figure 3C and D). This suggests that the decondensed X chromatin structure in DCC-depleted worms is not solely a result of the dispersing of the multiple copies of the X chromosome in the 32-ploid intestinal nuclei, but it is a result of defective compaction. We did not look at separate X chromosome territories in diploid cells because due to their small size only a small percentage of nuclei had clearly distinguishable X chromosome territories. Only 35% of both vector and dpy-27(RNAi) diploid nuclei clearly exhibited two separate X chromosome territories.Figure 3

Bottom Line: In addition, we show that SET-1, SET-4, and SIR-2.1, histone modifiers whose activity is regulated by the DCC, need to be present for the compaction of the X chromosome territory.These results support the idea that condensin I(DC), and the histone modifications regulated by the DCC, mediate interphase X chromosome compaction.Our results link condensin-mediated chromosome compaction, an activity connected to mitotic chromosome condensation, to chromosome-wide repression of gene expression in interphase.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109 Michigan.

ABSTRACT

Background: Dosage compensation is a specialized gene regulatory mechanism which equalizes X-linked gene expression between sexes. In Caenorhabditis elegans, dosage compensation is achieved by the activity of the dosage compensation complex (DCC). The DCC localizes to both X chromosomes in hermaphrodites to downregulate gene expression by half. The DCC contains a subcomplex (condensin I(DC)) similar to the evolutionarily conserved condensin complexes which play fundamental roles in chromosome dynamics during mitosis and meiosis. Therefore, mechanisms related to mitotic chromosome condensation have been long hypothesized to mediate dosage compensation. However experimental evidence was lacking.

Results: Using 3D FISH microscopy to measure the volumes of X and chromosome I territories and to measure distances between individual loci, we show that hermaphrodite worms deficient in DCC proteins have enlarged interphase X chromosomes when compared to wild type. By contrast, chromosome I is unaffected. Interestingly, hermaphrodite worms depleted of condensin I or II show no phenotype. Therefore X chromosome compaction is specific to condensin I(DC). In addition, we show that SET-1, SET-4, and SIR-2.1, histone modifiers whose activity is regulated by the DCC, need to be present for the compaction of the X chromosome territory.

Conclusion: These results support the idea that condensin I(DC), and the histone modifications regulated by the DCC, mediate interphase X chromosome compaction. Our results link condensin-mediated chromosome compaction, an activity connected to mitotic chromosome condensation, to chromosome-wide repression of gene expression in interphase.

No MeSH data available.


Related in: MedlinePlus