Proliferation and Differentiation of Pigment cells In Vitro

Abstract

The relationship between proliferation and melanin formation in monolayer cultures of mouse pigment cells was studied. Daily photographic records showed that a pigmented cell divided to form two pigmented daughter cells and a nonpigmented cell divided to form two nonpigmented ones. A pigmented cell proliferates to form a clonal colony of pigmented cells, all as pigmented as the parent cell. Almost all cells, whether pigmented or nonpigmented, have the ability to proliferate; hence the existence of a stem cell line is unlikely. The amount of melanin in a culture continues to increase after cell proliferation slows down. The melanin content of a cell decreases while the cells are proliferating logarithmically and increases rapidly when the rate of proliferation decreases. Results on radioisotope incorporation also show that when cells are at their peak of proliferative activity, their melanin-forming activity tends to be low; when proliferative activity declines, the rate of melanin synthesis rises rapidly. In the pigment cell line, genetic factors primarily determine the ability to form melanin. Within the limitation of the genetic make-up of these cells, melanin synthesis changes with cell density, the rate of proliferation, cell contact, and other environmental factors.