Somatic chromosomal changes of rat liver cells during in vitro cultivation

In order to examine how long diploid cells can be maintained in vitro cultivation without any chromosomal aberrations and to evaluate the mechanism of chromosomal heteroploid transformation, changes of chromosomes were studied in the course of serial in vitro transfers in four normal rat liver cell lines. As a result the diploid cells decreased in number gradually at early culture stage and disappeared completely in the periods between 350 and 500 days. The culture shifted to heteroploid as follow: diploidy---tpseudodiploidy---thypodiploidy---thypertriploidy or hypotetraploidy. This proces to heteroploid transformation is divided into five stages according to ploidy: 1- and II-stages show diploidy, III-stage, pseudodiploidy, IVstage, hypodiploidy and V-stage, hypertriploidy or hypotetraploidy. Chromosomal heteroploid transformation and neoploastic conversion occurred in IV-stage of the cultures. A possible mechanism involved in the process of chromosomal transformation was discussed.