Gene dosage effects in human diploid and tetraploid fibroblasts

The effects of cell ploidy on the biochemical characteristics of cultured cells were compared using human diploid vs tetraploid fibroblasts isolated with a non-selective method. Their DNA replication was compared by thymidine incorporation, and DNA content by Feulgen staining and quantitative analysis. Their RNA and protein content, cell sizes and the specific activities of glucose-6-phosphate dehydrogenase (G-6-PD) and 6-phosphogluconate dehydrogenase (6-PGD) were assayed quantitatively. With the exception of RNA content, all other parameters demonstrated a 2-fold increase reflecting the increase in cell ploidy. These direct gene dosage effects on the genetic material and functional expression of the human genome were in contrast to previous observations in other species and validate the use of human intraspecific euploid hybrids for biochemical and genetic studies.