Ploidy Fluctuations of Mouse Plasma-Cell Neoplasm MSPC-1 During Serial Transplantation

Summary

MSPC-1 plasma-cell neoplasm induced in BALB/c mice exhibited repeated tetraploidy during successive passages for 2 years. The cause for increased tetraploid frequency in this tumor was investigated. Neither pretreatment of host mice with γ rays nor double inoculation of diploids and tetraploids into a single host showed that the immunoselection mechanism of host animals directly affected the increase of tetraploid cells. Certain factors within the tumor cells seemed essential for facilitating tetraploidy. Whether repeated ploidy alteration was accompanied by cell population change was also studied. Analysis of marker chromosomes appearing additively during serial passages revealed that the cell population constituting one diploid phase is different from that of the next diploid phase, which is probably a variant of the former. Hypothetical processes of the repeated tetraploidy are proposed.