Translational control in sea urchin eggs and embryos: Initiation is rate limiting in blastula stage embryos

Abstract

To determine whether initiation is rate-limiting in protein synthesis during the embryogenesis of sea urchins, polyribosome profiles of unfertilized eggs and cleavage, blastula and prism stage embryos were examined after incubation of the eggs and embryos in the presence and absence of low amounts of emetine, an inhibitor of polypeptide elongation. The ribosomes were radioactively labeled with [ 3 H]uridine by injection of the adults during oogenesis so that we could monitor emetine-dependent shifts of monoribosomes to polyribosomes. Although initiation is not rate limiting in unfertilized eggs or 2-to 16-cell embryos of Strongylocentrotus purpuratus, it is rate limiting in blastula and prism embryos. We suggest that initiation becomes rate limiting to allow the selective translation of certain classes of mRNA during later development.

Stabilization of tubulin mRNA by inhibition of protein synthesis in sea urchin embryos.

“…Inhibition of protein synthesis in plutei had little effect on the prevalence of tubulin RNA (Fig. 3) (27,28) and pactamycin (17) at the concentrations used in this investigation. Moreover, in this investigation we confirmed the effects of these inhibitors on polysomes of embryos treated with colcemid and observed that tubulin mRNA behaves in the same way as the general population of mRNA in embryos treated with these agents.…”

“…This conclusion is based on the well-established effects of these protein synthesis inhibitors. The stabilization of polysomes in sea urchin embryos by treatment with the standard concentration of emetine has been demonstrated previously (27,28), as has the dissociation of polysomes by pactamycin at standard concentrations (17). To eliminate the possibility that colcemid treatment alters the action of these protein synthesis inhibitors, we analyzed the polysome profiles of embryos that were treated simultaneously with colcemid and one of these inhibitors.…”

“…5 (27) and had no effect on tubulin mRNA levels. Cycloheximide is considerably more effective when it is applied to mammalian cells; the inhibition of amino acid incorporation in CHO cells was stated by Pachter et al (33) Pachter et al (33) concluded that autogenous regulation of tubulin mRNA stability is independent of ongoing protein synthesis.…”

Regulation of sea urchin glycoprotein mRNAs during embryonic development

“…In sea urchin embryos, a lower capacity of mRNA from free ribonucleoprotein particles to bind ribosomes as compared to mRNA from polysomes has been reported (24). In addition, there is evidence indicating that initiation is ratelimiting in blastula-and prism-stage S. purpuratus embryos (32).…”

Poly(A)-Containing Messenger Ribonucleoprotein Complexes from Sea Urchin Eggs and Embryos: Polypeptides Associated with Native and UV-Crosslinked mRNPs

“…In order to determine how these ionic changes modulate protein synthesis, recent investigations have been made of the initiation and elongation steps, and of ribosome activity. Hille et al [13] have shown that the availability of recycling initiation factors is not ratelimiting in the egg, and that the major block in translation must be at some other step in initiation. Other investigations have shown that although the rate of polypeptide chain elongation increases approximately 2-3-fold after fertilization [4,121, this increased rate is clearly insuficient to account for the rapid kinetics of the post-feritilization increase in protein synthesis [14,351.…”