Fragile X expression in thymidine-prototrophic and auxotrophic human-mouse somatic cell hybrids under low and high thymidylate stress conditions.
Expression of the fragile X site fra(X)(q27.3) was studied in thymidine-prototrophic and auxotrophic human-mouse somatic cell hybrids. In these cells, low thymidylate stress, achieved by 5-fluoro-2'-deoxyuridine (FdU) treatment and by limiting the exogenous supply of thymidine (dT), induced fragile X expression. High thymidylate stress, produced by supplying excess amounts of dT, was also effective in inducing fragile X expression, even in a hybrid clone that retained a fragile X chromosome as the only human chromosome; addition of deoxycytidine (dC) completely abolished this effect. In contrast, 5-bromo-2'-deoxyuridine (BrdU) did not induce fragile X expression. Cell-cycle analysis of BrdU-deprived thymidine-auxotrophic hybrid cells indicated that one round of DNA replication under thymidylate stress conditions is sufficient for fragile X expression. Our results suggest that the expression is an intrinsic property of the fragile site itself, which is believed to be composed of replicon clusters with pyrimidine-rich DNA sequence(s).
Division of Genetics, National Institute of Radiological Sciences, Chiba, Japan.
T
T
Hori
E
E
Takahashi
H
H
Tsuji
S
S
Tsuji
M
M
Murata
D000818:Animals; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002453:Cell Cycle; D003845:Deoxycytosine Nucleotides / Q000502:physiology; D005600:Fragile X Syndrome / Q000235:genetics*; D005786:Gene Expression Regulation; D006801:Humans; D006822:Hybrid Cells; D008297:Male; D051379:Mice; D005810:Multigene Family; D012093:Replicon; D012729:Sex Chromosome Aberrations / Q000235:genetics*; D013936:Thymidine / Q000502:physiology; D013938:Thymidine Monophosphate / Q000494:pharmacology*; D013942:Thymine Nucleotides / Q000494:pharmacology* / Q000502:physiology
D003845:Deoxycytosine Nucleotides; D013942:Thymine Nucleotides; C024107:2'-deoxycytidine 5'-triphosphate; D013938:Thymidine Monophosphate; D001973:Bromodeoxyuridine; C024157:thymidine 5'-triphosphate; D013936:Thymidine