Chromosome breakage and xenotropic C-type virus in embryonic cultures from New Zealand black mice.

A considerable increase in chromatid and chromosome breaks, as well as excessive fragmentation and “pulverization” of whole metaphase plates was observed in embryonic fibroblast cultures from New Zealand black mice. A C-type RNA virus with a xenotropic host range was isolated from the supernatant fluid of co-cultures of NZB cells and heterologous permissive cells (SIRC cell line). One of the NZB cultures produced this virus without amplification by co-cultivation after spontaneous transformation of the cells. NZB cells are supposed to lack normal restriction of complete xenotropic virus expression and to release this endogenous virus spontaneously at a high level. It is hypothesized that the excessive chromosome damage observed in these cell cultures is related to the permanent production of virus, thus indicating a chromosome breaking effect of endogenous viruses.