Regulation of growth and gene activity in euploid hybrids between human neonatal fibroblasts and epithelioid amniotic fluid cells

Pure populations of proliferating synkaryons were obtained from polyethylene glycol-mediated crosses between diploid human foreskin fibroblasts and epithelioid amniotic fluid cells. These hybrids proved to be chromosomally stable tetraploids. They continually produced heteropolymeric G6PD and showed strictly additive patterns of silver staining of both parenteral sets of nucleolar organizing chromosomes. Collagenous proteins characteristic of the fibroblast parent were synthesized, while fibronectin production appeared to be directed by the epithelioid portion of the genome. Even though these heterotypic hybrids proliferated at a reduced rate and achieved fewer population doublings relative to homotypic (fibroblast x fibroblast) crosses, they survived passage by trypsinization better than pure populations of epithelioid cells. These observations suggest a concerted action of both parental genomes with respect to proteins responsible for 'household' functions, but complementation and possibly modulation of gene action with respect to 'luxury' protein synthesis and cell growth.