Ribosomal protein mRNAs increase dramatically during Xenopus development

The amount of messenger RNA per microgram of rRNA increases three- to fourfold during Xenopus early development. This increase is the same when measured by stimulation of in vitro protein synthesis or by poly(U) hybridization. The increase in mRNA per embryo therefore is approximately six- to eightfold since the ribosome content doubles between fertilization and the stage 41 tadpole. The amount of ribosomal protein mRNA, as assayed by in vitro protein synthesis, also increases dramatically during early development. This increase is much more pronounced than the general increase in mRNA content, i.e., there is a dramatic increase in the abundance as well as the amount of the ribosomal protein mRNA. Since ribosomal protein mRNAs are predominantly small mRNAs, the increase in ribosomal protein mRNA abundance contributes to the general decrease in the average size of pA⁺ RNA that occurs during early development in Xenopus.