Cytogenetic characterization of the transgenic Big Blue(R) Rat2 and Big Blue(R) mouse embryonic fibroblast cell lines

The transgenic Big Blue^® Rat2 and Big Blue^® mouse embryonicfibroblast cell lines have been used to complement the transgenicBig Blue® rat and mouse in vivo mutagenesis assays. However,limited information is available regarding the karyology ofthese cell lines. Therefore, we have characterized the ploidy,mitotic index, spontaneous frequencies of chromosome and chromatidaberrations and rate of micronucleus (MN) formation in bothcell lines. We have also characterized the frequency of sisterchromatid exchange (SCE) in transgenic Big Blue^® mouse cells.Big Blue^® Rat2 cells are hyperploid and have extremely highbaseline frequencies of cytogenetic damage. In addition, BigBlue^® Rat2 cells are BrdU-resistant, therefore, SCE frequenciescannot be assessed in these cells. We conclude that Big Blue^®Rat2 cells are not useful for routine cytogenetic toxicologystudies. The transgenic Big Blue^® mouse cell line is polyploidand consistently yields a low mitotic index (1%) in untreatedcells. These mouse cells also exhibited moderately high baselinefrequencies of chromosome and chromatid aberrations, however,baseline frequencies of SCE and of MN were not elevated. TransgenicBig Blue^® mouse embryonic fibroblasts were further studiedfor MN induction following treatment with Nethyl-N-nitrosourea(ENU) for 0.5 h at concentrations of 0.425,0.85 and 1.7 mM.Concentration-dependent increases in MN were observed in thesecells. Thus, while an ENU-induced cytogenetic response usingtransgenic Big Blue^® mouse cells demonstrates that thiscellular model could be used to cytogenetically complement themutagenesis assays, the low mitotic index and the high spontaneousfrequency of chromosome damage confounds its use for routinegenetic toxicology studies. ³To whom correspondence should be addressed. Tel: +1 919 541 3275; Fax: +1 919 541 1460; Email: tindall{at}niehs.nih.gov