Metaphase Chromosome Transfer of Introduced Selectable Markers

A general method for creating somatic cell hybrids which maintain chromosome segments by selection is described. To extend the technique of metaphase chromosome transfer to regions of the genome which do not carry a selectable marker, a retroviral vector has been employed to introduce the dominant selectable neo gene at many genomic locations in a population of murine cells. We have used such cells as donors in metaphase chromosome transfer experiments in which hamster and monkey cells were used as recipients. Cells acquiring a transferred chromosomal segment containing the neo gene were selected by growth in the presence of the drug G418. Hybridization to cloned interspersed repeat DNA sequences of the mouse was used to estimate the proportion of mouse DNA in each transferent. These experiments indicate that transferents produced in this manner contain 0.01 to 1.0% of the mouse genome. To analyze the organization of the DNA transferred to each recipient, we used Southern transfer hybridization of DNA from each transferent to a cloned mouse interspersed repeated DNA probe which did not cross-hybridize to hamster or monkey DNA. We found that each primary transferent gave a unique pattern of restriction fragments hybridizing to this probe. Secondary transferents from two independent primary transferents were compared by this technique. Each set of secondary transferents exhibited a hybridization pattern which resembled closely that of the primary transferent from which it was derived. However, a number of hybridizing DNA segments present in each primary transferent were absent in some of the secondary transferents. These results are most compatible with the view that an intact segment of the mouse chromosome surrounding the integration site of the retroviral vector can be transferred by the techniques used in this study. We believe this technique will be generally applicable to cells from many species, and will allow the study of chromosome regions previously refractory to analysis by chromosome transfer techniques.