Involvement of V(D)J recombinase in the generation of intragenic deletions in the Rit1/Bcl11b tumor suppressor gene in gamma-ray-induced thymic lymphomas and in normal thymus of the mouse.
Mouse thymic lymphomas induced by gamma-irradiation exhibited homozygous deletions of the Rit1/Bcl11b tumor suppressor gene on chromosome 12 at high frequencies. Internal deletions of one allele were frequently accompanied by loss of the other allele. In order to elucidate the mechanism of these internal deletions, the sites of breakage and rejoining were examined by PCR mapping and sequencing. The 5' site of the deletions clustered within an approximately 5 kb region of intron 1 and the 3' site was confined to a site in intron 3. These sites contained P and/or N nucleotides and cryptic sequences recognizable by the RAG1/2 recombinase in the vicinity. This suggests that the Rit1 intragenic deletions were generated by endogenous illegitimate V(D)J recombinase activity and such aberrant recombination was also detected by nested PCR of DNA from the thymus of unirradiated mice but not of RAG2-deficient mice. A rough estimate indicated that there reside as many as 10(3)-10(4) thymocytes having Rit1 deletions, assuming the presence of 10(8) thymocytes in the thymus of unirradiated mice. Moreover, the recombination frequency was not affected by gamma-irradiation. These results show no effect of radiation on Rit1 mutations and suggest an indirect mechanism for its role in lymphomagenesis.
Sakata
Jun
J
Department of Molecular Genetics, Graduate School of Medical and Dental Sciences, Niigata University, Asahimachi 1-757, Niigata 951-8122, Japan.
Inoue
Jun
J
Ohi
Hiroyuki
H
Kosugi-Okano
Hitomi
H
Mishima
Yukio
Y
Hatakeyama
Katsuyoshi
K
Niwa
Ohtsura
O
Kominami
Ryo
R
D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D005260:Female; D005720:Gamma Rays; D017353:Gene Deletion; D008223:Lymphoma / Q000201:enzymology / Q000209:etiology / Q000235:genetics*; D008297:Male; D051379:Mice; D009381:Neoplasms, Radiation-Induced / Q000201:enzymology / Q000209:etiology / Q000235:genetics*; D013950:Thymus Gland / Q000201:enzymology / Q000378:metabolism*; D013953:Thymus Neoplasms / Q000201:enzymology / Q000209:etiology / Q000235:genetics*; D045567:VDJ Recombinases / Q000378:metabolism*; D018631:ras Proteins / Q000235:genetics*
D017931:DNA Primers; D045567:VDJ Recombinases; C472865:Rit1 protein, mouse; D018631:ras Proteins