SELECTION IN-VIVO IN CELL-POPULATIONS OF RAT RA-23 RHABDOMYOSARCOMA AT THE TRAIT FREQUENCY OF CELLS WITH BRIDGES

Selection in vivo of cell clones of rat transplantable organospecific rhabdomyosarcoma RA-23 for increased and decreased frequencies of cell s with chromosomal bridges (FCB) was performed. The initial average FC B in clones was 0.8% at a range of variation of from 0 to 3.0%. Select ion for an increase, as well as for a decrease, in the FCB in RA-23 cl ones was effective. After one step of selection for an increase in the FCB, the average FCB increased to 3.0%. Thereafter, selection for an increase in the FCB was impracticable due to loss of transplantability in cell populations in which the FCB exceeded 5.0%. Over five steps o f selection for a decrease in the FCB, the average FCB significantly d ecreased to 0.3% (P < 0.001). The heritability coefficient h(2) of the trait FCB upon selection ranged from 0.25 to 0.30. The high and low F CBs attained by selection correlated with the index ''frequency of cel ls with micronuclei.'' The population of RA-23 cells after selection f or a decrease in the FCB differed from the population of cells of the original RA-23 strain by significantly lower karyotypic heterogeneity. The values of h(2) obtained upon selection for the FCB and the effect iveness of selection for an increase, as well as for a decrease, in th e FCB show that, with selection at the trait ''frequency of cells with bridges,'' which characterizes the stability of the karyotype, existi ng cell strains can be subjected to karyotypic stabilization or destab ilization.