Gene expression in sea urchin development.

Actinomycin D has been administered for various lengths of time and at various concentrations to developing sea urchin embryos. The results obtained support the following suggestions. (1) The shape of respiratory curve up to the mesenchyme blastula stage is not under direct gene control. (2) The RNA needed for gastrulation seems to be made during the period between early and late blastula. (3) The RNA needed for skeleton differentiation is continously made from some time before early gastrula throughout skeleton growth. (4) The process of development of skeleton is extremely sensitive to actinomycin.