A staining procedure for identifying viable cell hybrids constructed by somatic cell fusion, cybridization, or nuclear transplantation.

A general procedure for identifying viable hybrid cells was developed. One cell type was labeled by a brief incubation in the Kodak laser dye rhodamine 123, which accumulates in the mitochondria; a second cell type was labeled by a brief incubation in the Hoechst fluorochrome 33258, which binds to chromatin. The substances which are eventually lost from the organelles, appeared to be nontoxic; the plating efficiencies of numerous cell lines tested was unaffected. Either whole cells or cytoplasts labeled with rhodomine 123 were fused, using inactivated Sendai virus, to whole cells or karyoplasts labeled with Hoechst 33258. When living cells were illuminated with ultraviolet light, individual whole cell hybrids, cybrids or cytoplasmic- nuclear hybrid cells could be rapidly identified by the appropriate staining pattern.