Cell-free translation analysis of messenger RNA in echinoderm and amphibian early development

A wheat germ cell-free translation system has been used to analyze populations of abundant messenger RNA from sea urchin eggs and embryos and from amphibian oocytes and ovaries. We show directly that sea urchin eggs and embryos contain translatable mRNA of three general classes: poly(A)⁺ mRNA, poly(A)^- histone mRNA, and poly(A)^- nonhistone mRNA. Additionally, some histone synthesis appears to be promoted by poly(A)⁺ RNA. Sea urchin eggs seem to contain a higher proportion of prevalent poly(A)^- nonhistone mRNAS than do embryos. Some differences in the proteins encoded by poly(A)⁺ and poly(A)^- RNAs are detectable. Many coding sequences in the egg appear to be represented in both poly(A)⁺ and poly(A)^- RNAs, since the translation products of the two RNA classes exhibit many common bands when run on one-dimensional polyacrylamide gels. However, some of this overlap is probably due to fortuitous comigration of nonidentical proteins. Distinct stage-specific changes in the spectra of prevalent translatable mRNAs of all three classes occur, although many mRNAs are detectable throughout early development. Particularly striking is the presence of an egg poly(A)^- mRNA, encoding a 70,000-80,000 molecular weight protein, which is not detected in morula or later-stage embryos. In amphibian (Xenopus laevis and Triturus viridescens) ovary RNA, the translation assay detects the following three mRNA classes: poly(A)⁺ nonhistone mRNA, poly(A)^- histone mRNA, and poly(A)⁺ histone mRNA. Amphibian ovary RNA appearently lacks an abundant poly(A)^- nonhistone mRNA component of the magnitude detectable in sea urchin eggs. mRNA encoding histone-like proteins is found in the very earliest (small stage 1) oocytes of Xenopus as well as in later stage oocytes. During oogenesis there appear to be no striking qualitative changes in the spectra of prevalent translatable mRNAs which are detected by the cell-free translation assay.