Have double minutes functioning centromeres?

Normally, double minute (DM) chromosomes are extremely difficult to observe at other mitotic stages than prophase and metaphase. In a certain clonal subline of the mouse ascites tumor SEWA, however, the DMs were unusually distinct and could be followed through all mitotic stages. Their behavior was extraordinary: During metaphase-anaphase they exhibited no response whatever towards the spindle forces, and it was concluded that the DMs were without functioning centromere. Instead, at metaphase they were attached to or enclosed by the nucleolar matter persisting around the chromosome ends, and at anaphase they were transported to the poles together with the nucleolar matter, sticking to the daughter chromosomes. The daughter halves of each DM were usually carried to the same pole. Thus most of the DMs, in spite of their lack of detectable centromeric activity, were included into the telophase nuclei. Some micronuclei were found, however, probably leading to the loss of a proportion of the DMs. The content of DMs in a certain tumor cell population therefore must depend on the balance between this loss and the gain due to a positive selection value of cells containing DMs.