Human chromosome fragility
- PMID: 18078840
- DOI: 10.1016/j.bbagrm.2007.10.005
Human chromosome fragility
Abstract
Fragile sites are heritable specific chromosome loci that exhibit an increased frequency of gaps, poor staining, constrictions or breaks when chromosomes are exposed to partial DNA replication inhibition. They constitute areas of chromatin that fail to compact during mitosis. They are classified as rare or common depending on their frequency within the population and are further subdivided on the basis of their specific induction chemistry into different groups differentiated as folate sensitive or non-folate sensitive rare fragile sites, and as aphidicolin, bromodeoxyuridine (BrdU) or 5-azacytidine inducible common fragile sites. Most of the known inducers of fragility share in common their potentiality to inhibit the elongation of DNA replication, particularly at fragile site loci. Seven folate sensitive (FRA10A, FRA11B, FRA12A, FRA16A, FRAXA, FRAXE and FRAXF) and two non-folate sensitive (FRA10B and FRA16B) fragile sites have been molecularly characterized. All have been found to represent expanded DNA repeat sequences resulting from a dynamic mutation involving the normally occurring polymorphic CCG/CGG trinucleotide repeats at the folate sensitive and AT-rich minisatellite repeats at the non-folate sensitive fragile sites. These expanded repeats were demonstrated, first, to have the potential, under certain conditions, to form stable secondary non-B DNA structures (intra-strand hairpins, slipped strand DNA or tetrahelical structures) and to present highly flexible repeat sequences, both conditions which are expected to affect the replication dynamics, and second, to decrease the efficiency of nucleosome assembly, resulting in decondensation defects seen as fragile sites. Thirteen aphidicolin inducible common fragile sites (FRA2G, FRA3B, FRA4F, FRA6E, FRA6F, FRA7E, FRA7G, FRA7H, FRA7I, FRA8C, FRA9E, FRA16D and FRAXB) have been characterized at a molecular level and found to represent relatively AT-rich DNA areas, but without any expanded repeat motifs. Analysis of structural characteristics of the DNA at some of these sites (FRA2G, FRA3B, FRA6F, FRA7E, FRA7G, FRA7H, FRA7I, FRA16D and FRAXB) showed that they contained more areas of high DNA torsional flexibility with more highly AT-dinucleotide-rich islands than neighbouring non-fragile regions. These islands were shown to have the potential to form secondary non-B DNA structures and to interfere with higher-order chromatin folding. Therefore, a common fragility mechanism, characterized by high flexibility and the potential to form secondary structures and interfere with nucleosome assembly, is shared by all the cloned classes of fragile sites. From the clinical point of view, the folate sensitive rare fragile site FRAXA is the most important fragile site as it is associated with the fragile X syndrome, the most common form of familial mental retardation, affecting about 1/4000 males and 1/6000 females. Mental retardation in this syndrome is considered as resulting from the abolition of the FMR1 gene expression due to hypermethylation of the gene CpG islands adjacent to the expanded methylated trinucleotide repeat. FRAXE is associated with X-linked non-specific mental retardation, and FRA11B with Jacobsen syndrome. There is also some evidence that fragile sites, especially common fragile sites, are consistently involved in the in vivo chromosomal rearrangements related to cancer, whereas the possible implication of common fragile sites in neuropsychiatric and developmental disorders is still poorly documented.
Similar articles
-
Fragile sites, chromosomal lesions, tandem repeats, and disease.Front Genet. 2022 Nov 17;13:985975. doi: 10.3389/fgene.2022.985975. eCollection 2022. Front Genet. 2022. PMID: 36468036 Free PMC article. Review.
-
Folate-sensitive fragile site FRA10A is due to an expansion of a CGG repeat in a novel gene, FRA10AC1, encoding a nuclear protein.Genomics. 2004 Jul;84(1):69-81. doi: 10.1016/j.ygeno.2003.12.017. Genomics. 2004. PMID: 15203205
-
Molecular basis for expression of common and rare fragile sites.Mol Cell Biol. 2003 Oct;23(20):7143-51. doi: 10.1128/MCB.23.20.7143-7151.2003. Mol Cell Biol. 2003. PMID: 14517285 Free PMC article.
-
Common fragile sites and cancer (review).Int J Oncol. 1998 Jan;12(1):187-96. Int J Oncol. 1998. PMID: 9454904 Review.
-
Isolation of a GCC repeat showing expansion in FRAXF, a fragile site distal to FRAXA and FRAXE.Nat Genet. 1994 Nov;8(3):229-35. doi: 10.1038/ng1194-229. Nat Genet. 1994. PMID: 7874164
Cited by
-
Genetic Analysis of a Mosaic Fra(16)(q22)/Del(16)(q22) Karyotype in a Primary Infertile Woman.Int J Womens Health. 2024 Apr 16;16:637-644. doi: 10.2147/IJWH.S450272. eCollection 2024. Int J Womens Health. 2024. PMID: 38645979 Free PMC article.
-
Identification of Genomic Instability in Cows Infected with BVD Virus.Animals (Basel). 2023 Dec 9;13(24):3800. doi: 10.3390/ani13243800. Animals (Basel). 2023. PMID: 38136837 Free PMC article.
-
MutSβ protects common fragile sites by facilitating homology-directed repair at DNA double-strand breaks with secondary structures.Nucleic Acids Res. 2024 Feb 9;52(3):1120-1135. doi: 10.1093/nar/gkad1112. Nucleic Acids Res. 2024. PMID: 38038265 Free PMC article.
-
DEK oncoprotein participates in heterochromatin replication via SUMO-dependent nuclear bodies.J Cell Sci. 2023 Dec 1;136(23):jcs261329. doi: 10.1242/jcs.261329. Epub 2023 Dec 15. J Cell Sci. 2023. PMID: 37997922 Free PMC article.
-
Effect of Selected Micro- and Macroelements and Vitamins on the Genome Stability of Bovine Embryo Transfer Recipients following In Vitro Fertilization.Animals (Basel). 2023 Mar 14;13(6):1056. doi: 10.3390/ani13061056. Animals (Basel). 2023. PMID: 36978597 Free PMC article.
Publication types
MeSH terms
Substances
LinkOut - more resources
Full Text Sources