DNA content of nuclei and chromosome number in sublines of the Ehrlich ascites carcinoma.

The study of metaphase chromosomes of ascites tumors has shown that, for a given strain of tumor, there is found a characteristic modal chromosome number (referred to as «),which frequently lies near that of the diploid number for the host organism (3). Other tumors have modal numbers in the tetraploid range, this condition appearing to enhance the ability of the tumor cells to grow in host strains other than that in which the tumor originateli. Recently, it has become possible to study the effect of such doubling of chromosome number in closely related sublines. From the pre dominantly hyperdiploid (s = 45-46) LettréEhrlich ascites carcinoma, Kaziwara (4) was able to select sublines consisting largely of the hypertetraploid cells (2«= 90-92) normally present with low frequency in the parent strain. The subline EL88 appeared to be stable and suitable for use in investigations of the effect of doubled chromosome number on the physiology of the tumor cells. A recent study from this laboratory (10) is concerned with the differences in peptidase content of the «and 2s cells of these types. Biochemical and cytochemical (Feulgen) studies of DNA and chromosome number carried out in connection with this work showed nuclear phe nomena in the EL88 subline not expected on the basis of its earlier history. There occurred a high rate of reversion to the s condition and a high fre quency of cells with DNA contents beyond the octoploid range. The latter effect indicates that cells of high ploidy were present with frequencies not evident from analysis of the metaphase counts. This, as well as further work with the chromosome number and DNA content of these sublines, is reported below.