Formation of extrachromosomal circles from telomeric DNA in Xenopus laevis.
Instability and plasticity of telomeric DNA, which includes extrachromosomal DNA, are usually correlated with the absence of telomerase and with abnormal growth of mammalian cells. Here, we show the formation of extrachromosomal circular DNA of telomeric repeats (tel-eccDNA) during the development of Xenopus laevis. Tel-eccDNA is double-stranded relaxed circles composed of the vertebrate consensus telomeric repeats [TTAGGG](n). Its size varies from <2 to >20 kb and it comprises up to 10% of the total cellular telomere content of the early embryo (pre-MBT stage). The amount of tel-eccDNA is reduced in later developmental stages and in adult tissues. Using a cell-free system derived from Xenopus egg extracts, we show that tel-eccDNA can be formed de novo from the telomere chromosomal tracts of sperm nuclei and naked DNA in a replication-independent manner. These results reveal an unusual plasticity of telomeric DNA during normal development of Xenopus.
Cohen
Sarit
S
Institute of Human Genetics, CNRS, Genome Dynamics and Development, 141 rue de la Cardonille, 34396 Montpellier cedex 5, France.
Méchali
Marcel
M
D000818:Animals; D004261:DNA Replication / Q000235:genetics / Q000502:physiology; D004270:DNA, Circular / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D066298:In Vitro Techniques; D015335:Molecular Probes; D016615:Telomere / Q000235:genetics* / Q000378:metabolism; D014981:Xenopus
D004270:DNA, Circular; D015335:Molecular Probes