The effects of RNA synthesis inhibition and of protein synthesis inhibition on embryonic induction and cell differentiation in Rana pipiens

Presumptive epidermis cells of Rana pipiens gastrula (stage 11) was induced in vitro by LiCl to differentiate into melanophores. The period from the moment when the inductor was introduced to the cells to the moment of their morphological differentiation was arbitrarily divided into three stages: “A” — The time interval during which the cells were exposed to LiCl, “B” — The period of several hours immediately following the cells' contact with the inductor, and “C” — The period of time immediately preceding formation of pigment in the cells. During one of these three stages the cells were treated with one of the three inhibitors: actinomycin, puromycin or ethionine. Differential sensitivity of the activated cells to the inhibitor during these three stages was revealed by their subsequent differentiation. Puromycin when applied at stage “A” increased pigmentation of melanocytes. Actinomycin acting during stage “B” in some cases caused differentiation of mesenchyme‐like cells instead of melanophores. Ethionine presented to the cells at stage “C” promoted differentiation of a characteristic cell type which could not be identified with any normal histological species.