Does protein synthesis decline in lithium-treated sea urchin embryos because RNA synthesis is inhibited?

Vegetalization of sea urchin embryos by Li⁺ is characterized by rates of protein synthesis which are normal during cleavage, and decline after hatching. This paper tests the hypothesis that Li⁺ interferes with RNA synthesis during cleavage, resulting in the decline in protein synthesis at hatching when newly synthesized mRNA becomes critical for further normal development. Treatment with Li⁺ does cause a decline in the incorporation of ³H]guanosine into RNA. However, this decline could be accounted for by reduced uptake of the labeled precursor with a concomitant reduction in precursor pool specific activity. Therefore, reduced protein synthesis after hatching in Li⁺-treated embryos cannot be accounted for by a comparable reduction in RNA synthesis.