Regulation of sea urchin glycoprotein mRNAs during embryonic development

Gastrulation in sea urchin embryos is accompanied by a striking increase in the synthesis of N-linked glycoproteins, and inhibitors of this process block gastrulation. In this report, the messages coding for N-glycosylatable proteins in the developing embryo of the sea urchin, Strongylocentrotus purpuratus, were examined. Total mRNA and mRNA isolated from membranes of the embryos at various stages of development were used to program a cell-free translation/glycosylation system prepared from rabbit reticulocyte lysate supplemented with dog pancreas microsomes. The glycosylated translation products were separated from the nonglycosylated products by concanavalin A-agarose and analyzed by gel electrophoresis. The results indicate that although the RNA derived from the membranes of gastrula-stage embryos contains messages coding for numerous glycoproteins, only trace amounts of glycoprotein messages are associated with membranes at earlier stages of development. mRNAs coding for four glycoproteins of M(r)s 70,000, 65,000, 51,000, and 30,000 were examined further in total RNA preparations from the developing embryo. The data indicate that the messages coding for the glycoproteins of M(r)s 65,000 and 51,000 are present also in the unfertilized egg and in the pregastrulation embryo. Because these two messages are not found associated with the membranes until gastrula stage, it is likely that the synthesis of these glycoproteins during gastrulation is regulated at the translational level. The messages coding for glycoproteins of M(r)s 70,000 and 30,000, on the other hand, are not detectable in the unfertilized egg and may be synthesized de novo by the embryos. Thus, the expression of these two glycoproteins during gastrulation is regulated at least in part on the transcriptional level. On the basis of these findings, it appears that different modes of regulation are used for different glycoproteins that are synthesized during gastrulation.