Heterochromatin: Constitutive


Heterochromatin consists of a variety of nontranscribed tandemly repeated and interspersed repetitive deoxyribonucleic acid DNA sequences. The major classes of tandemly repeated DNA are: satellite DNA, composed of very long arrays mainly found in and around centromeres; minisatellite DNA, composed of moderately sized arrays located at or close to telomeres; and microsatellites, defined by short arrays and dispersed throughout the human genome. long interspersed nuclear elements and short interspersed nuclear elements are the two major classes of interspersed repeats, also referred to as transposon‐derived repeats. Rare fragile sites involve large expansions of microsatellites or minisatellites.

Keywords: heterochromatin; satellite DNA; LINEs, SINEs; minisatellites; centromere‐associated proteins; fragile sites

Figure 1.

Half karyotypes from metaphases showing the CBG bands (C bands by barium hydroxide using Giemsa) (left) and the double distamycin A/4,6‐diamino‐2‐phenol‐indole (DA/DAPI) staining (right).

Figure 2.

Location of different classes of satellite DNA (indicated by differently shaded regions) at the centromeric and pericentromeric regions of the idiogrammed chromosomes 1, 9, 14, 16 and Y. The arrowed black square brackets to the left of each chromosome indicate the major sites of methylcytosine‐rich heterochromatin.

Figure 3.

General distribution of interspersed LINE‐1 and SINE‐Alu sequences (black arrows) and tandemly repeated DNA (differently shaded regions) on an idealized chromosome. The arrowed black square brackets to the left indicate the sites of methylcytosine‐rich heterochromatin corresponding to T bands.

Figure 4.

Hybridization of conserved alphoid (p82H) and telomeric sequences in the centromeric and telomeric regions of metaphase chromosomes. The probes (bright spots) are detected using fluoresceinisothiocyanate (FITC). The chromosomes are counterstained with 4,6‐diamino‐2‐phenol‐indole (DAPI).

Figure 5.

Partial QFQ‐banded metaphases showing chromosome breaks at the expressed rare folate‐sensitive fragile site fra(10)(q23.3) or fra(10)(q24.2) (FRA10A) (a) and the common aphidicolin inducible fragile site, fra(7)(q36) (FRA7I) (b).



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Further Reading

Ballif BC, Kashork CD and Shafer LG (2000) The promise and pitfalls of telomere region‐specific probes. American Journal of Human Genetics 67: 1356–1359.

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Web Links

Caveolin 1, caveolae protein, 22 kDa (CAV1); Locus ID: 857. LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=857

Caveolin 2 (CAV2); Locus ID: 858. LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=858

Fragile site, aphidicolin type, common, fra(3)(p14.2) (FRA3B); Locus ID: 2385. LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=2385

Fragile site, aphidicolin type, common, fra(7)(q31.2) (FRA7G); Locus ID: 2414. LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=2414

WW domain containing oxidoreductase (WWOX); Locus ID: 51741. LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/LocRpt.cgi?l=51741

Caveolin 1, caveolae protein, 22 kDa (CAV1); MIM number: 601047. OMIM: http://www.ncbi.nlm.nih.gov/htbin‐post/Omim/dispmim?601047

Caveolin 2 (CAV2); MIM number: 601048. OMIM: http://www.ncbi.nlm.nih.gov/htbin‐post/Omim/dispmim?601048

Fragile site, aphidicolin type, common, fra(3)(p14.2) (FRA3B); MIM number: 601153. OMIM: http://www.ncbi.nlm.nih.gov/htbin‐post/Omim/dispmim?601153

Fragile site, aphidicolin type, common, fra(7)(q31.2) (FRA7G); MIM number: 606085. OMIM: http://www.ncbi.nlm.nih.gov/htbin‐post/Omim/dispmim?606085

WW domain containing oxidoreductase (WWOX); MIM number: 605131. OMIM: http://www.ncbi.nlm.nih.gov/htbin‐post/Omim/dispmim?605131

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How to Cite close
Larizza, Lidia, and Doneda, Luisa(Jan 2006) Heterochromatin: Constitutive. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0005786]