A novel minisatellite repeat expansion identified at FRA16B in a Japanese carrier.
Previously, the allelic expansion of a 33-bp AT-rich minisatellite repeat has been reported to cause FRA16B, a distamycin A-inducible fragile site. Here, we identified a novel 35-bp minisatellite repeat at FRA16B in a Japanese carrier. The nucleotide sequence of the 35-bp minisatellite was highly AT-rich and nearly identical to the 33-bp one but with insertion of two nucleotides, thymine and adenine. The copy number of the AT-rich minisatellite was 21 in total in the carrier, while only a few copies of the 33-bp minisatellite were present in a non-carrier Japanese subject. These results suggest that the molecular mechanism involved in the allelic expansion of the minisatellite repeat in FRA16B recognizes both minisatellites, the 33-bp one and the 35-bp one, as an amplicon. These observations were different from the ones at folate-sensitive fragile sites, where the CCG triplet repeat was commonly involved in the allelic expansion. Although a slight reduction in AT content (95% > 90%) in the region of minisatellite expansion in the carrier subject was observed, both AT-content and length of the highly AT-rich region seem to play important roles in the cytogenetic expression of the distamycin A-inducible fragile site. In another normal subject, without fragile site expression, allelic expansion involving the 33-bp minisatellite was observed, and the length of the AT-rich DNA region was increased up to approximately 1000 bp. Since the length of the AT-rich minisatellite region was increased up to approximately 1,100-bp in the carrier subject, the threshold length for the cytogenetic expression of the AT-rich DNA region may be between about 1,000-bp and 1,100-bp.
Yamauchi
M
M
Genome Research Group, National Institute of Radiological Sciences, Chiba, Japan. m_yam@nirs.go.jp
Tsuji
S
S
Mita
K
K
Saito
T
T
Morimyo
M
M
D044466:Asian People / Q000235:genetics*; D001483:Base Sequence; D002460:Cell Line; D043283:Chromosome Fragile Sites; D002873:Chromosome Fragility; D018076:DNA, Complementary; D015870:Gene Expression; D006579:Heterozygote; D006801:Humans; D007564:Japan; D018598:Minisatellite Repeats; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods; D017422:Sequence Analysis, DNA
D018076:DNA, Complementary