Properties of the three cell types in sixteen-cell sea urchin embryos: RNA synthesis

Abstract

RNA synthesis was studied in 16-cell stage embryos, separated cells from that stage, and reaggregates of the cells. At the 16-cell stage synthesis of nuclear RNA predominates: mRNAs are also synthesized. tRNA and rRNA are not made at detectable levels. All cell types incorporate 5- 3 H-uridine into RNA at the same rate, and the size classes of newly made RNA are the same in all three cell types. After separation, the incorporation of radioactive precursors is reduced but all cells are alive and incorporate precursors into DNA, RNA, and protein. This reduction in incorporation is probably due to changes in precursor pools and/or permeability. The pattern of RNA synthesis is not measurably changed by separation. After culture for 15–20 hours, all three cell types show an activation of synthesis of rRNA and tRNA, as do normal embryos. This activation is not dependent on aggregation, since it occurs both in aggregates and cells which are cultured without aggregation.