Abstract
The growth kinetics and population doubling limits of chick embryonic fibroblasts, chondroblasts, and retinal pigment cells were compared. Chondroblasts were found to have a cumulative population doubling level (37 ± 3 PDL) similar (p = 0.05) to that of control fibroblasts (42 ± 2 PDL), in individual and pooled clones. While both cell types have similar doubling potential, the proportion of tritium‐labeled nuclei decreases, and differs significantly as doubling level increases. This age‐associated decline is due to an extension in the population doubling time. Direct cell‐cycle analysis shows this increase to occur in the G~1~ phase. Furthermore, cartilage colonies maintain their phenotypic expression (metachromasia) throughout their lifespan under conditions of subcloning at sparse density.
When fibroblasts derived from 15 day chick embryos are compared with fibroblasts from 10 day embryos (41 ± 2 PDL) there is no significant difference (p = 0.05) in cumulative PDL or percent labeled nuclei, indicating that fibroblasts of different embryonic age have similar potential. The addition of hydrocortisone and insulin to the medium significantly shortens (25 ± 2 PDL) the lifespan of 10 day chick fibroblasts. Kinetics of retinal pigment cells show a population doubling potential (29 ± 1 PDL) different from fibroblasts and chondroblasts, suggesting that different cell types may not have similar limits on doubling potential when first determined in embryogenesis. Hydrocortisone and insulin have no effect on the growth kinetics or lifespan of retinal pigment cells in culture.