[A cytogenetic analysis of the cells of spontaneously transformed LREC rat cell lines. I. Chromosomal rearrangements detected in the early stages of rat embryonic cell transformation in vitro].

Seven spontaneously transformed cell lines LREC of rat embryo fibroblasts were obtained by an originally elaborated cloning technique (method 2T7). Six lines (1-6) were obtained from Rattus norvegicus cells, and one line (LREC-7) from Wistar rats. Method 2T7 was based on a serial propagation of rat embryo cells, brought to a "crisis" stage under conditions of a higher cell density and followed by the appearance of actively proliferating cell clones. These lines were analysed cytogenetically at the earliest stages using the Giemsa G-banding technique. In the karyotypes of six LREC (1-6) lines two abnormal chromosomes 7 were revealed: one marker chromosome M1-t(7; 19) results from translocation between chromosomes 7 and 19, the other marker chromosome M2--del(7) is a result of deletion of the second homolog of chromosome 7 in the q11.2 q22.1 loci; besides an extra normal homolog of chromosome 7 was revealed. There are only two marker chromosomes M2 in the LREC-7 line karyotype. Cells of LREC (1-3) lines could be transformed from the immortalized stage to the malignant one by the 30-45th passages. The cells of LREC (4, 7) lines became malignant at the 10-8th passages, resp. The rearrangements of chromosome 7 are supposed to be specific for LREC lines obtained by our method. A hypothesis is put forward that the translocation of chromosome 7 may play an important role for the immortalization of the rat embryo cells. The deletion of chromosome 7 may be associated with a malignant transformation of cells, as it is possible that the deleted loci have a recessive oncogene. Method 2T7 allows to obtain constantly spontaneously transformed cell lines of rat embryo cells with the least abnormal karyotype.