CHARACTERIZATION OF SOMATIC-CELL HYBRIDS EXHIBITING EXTINCTION OF AFP, ALBUMIN AND AN AFP-HPRT TRANSGENE

We utilized an AFP-HPRT transgene, i.e. the HPRT coding sequences unde r the regulation of AFP enhancer and promoter sequences, to localize t he AFP extinguisher locus in intertypic somatic cell hybrids (hepatoma X fibroblast). This hybrid gene construct, which directly links AFP r egulation to a reversibly selective gene, enabled the selection of sta bly transfected cells which express AFP, as well as cells showing exti nction of AFP. Mouse hepatoma cells stably transfected with and expres sing the transgene were fused to human fibroblasts, and the resulting somatic cell hybrids were characterized using Southern, Northern and k aryotypic analyses. That several hybrids exhibited the proper extincti on of AFP, AFP-HPRT and albumin suggests coregulation of these genes b y an extinguisher: Segregant lines derived from these hybrids were sel ected for the loss of extinguisher activity and for reexpression of th e transgene. Karyotypic analysis of hybrid and segregant lines, exhibi ting proper AFP, albumin and AFP-HPRT phenotypes, revealed that the pr esence of human chromosome 7 was most closely associated with the AFP- extinguished stare. The hybrids generated in these studies now make it possible to isolate the sequences responsible for AFP and albumin ext inction.