Embryonic-stage-dependent changes in the level of eIF4E-binding proteins during early development of sea urchin embryos

Abstract

The eukaryotic initiation factor 4E (eIF4E)-binding proteins (4E-BPs) inhibit translation initiation by binding eIF4E and preventing recruitment of the translation machinery to mRNA. We have previously shown that fertilization of sea urchin eggs triggers eIF4E–4E-BP complex dissociation and 4E-BP degradation. Here, we show that microinjection of eIF4E-binding motif peptide into unfertilized eggs delays the onset of the first mitosis triggered by fertilization, demonstrating that dissociation of the eIF4E–4E-BP complex is functionally important for the first mitotic division in sea urchin embryos. We also show by gel filtration analyses that eIF4E is present in unfertilized eggs as an 80 kDa molecular mass complex containing 4E-BP and a new 4E-BP of 40 kDa. Fertilization triggers the dissociation of eIF4E from these two 4E-BPs and triggers the rapid recruitment of eIF4E into a high-molecular-mass complex. Release of eIF4E from the two 4E-BPs is correlated with a decrease in the total level of both 4E-BPs following fertilization. Abundance of the two 4E-BPs has been monitored during embryonic development. The level of the two proteins remains very low during the rapid cleavage stage of early development and increases 8 hours after fertilization. These results demonstrate that these two 4E-BPs are down- and upregulated during the embryonic development of sea urchins. Consequently, these data suggest that eIF4E availability to other partners represents an important determinant of the early development of sea urchin embryos.

Modelization of the regulation of protein synthesis following fertilization in sea urchin shows requirement of two processes: a destabilization of eIF4E:4E-BP complex and a great stimulation of the 4E-BP-degradation mechanism, both rapamycin-sensitive

“…It has been already reported that FRAP/mTOR is involved in the protein synthesis increase following fertilization (Salaun et al, 2003, 2004, 2005; Oulhen et al, 2007). The effect of rapamycin, an inhibitor of the protein kinase FRAP/mTOR, has been analyzed in early development of sea urchin embryo.…”

“…Fertilization triggers 4E-BP release from eIF4E and consequently protein synthesis translation through a rapamycin-, and thus, mTOR-sensitive pathway (Cormier et al, 2001; Salaun et al, 2003, 2004). An original mechanism of 4E-BP regulation first demonstrated in sea urchin, corresponds to the rapid disappearance of 4E-BP pool following fertilization (Salaun et al, 2003, 2004, 2005; Oulhen et al, 2007, 2009). Although fertilization is known to provoke many changes in the egg metabolism that could interfere on translation regulation (Epel, 1990; Gilbert, 2003; Parrington et al, 2007), we demonstrate here that a reduced model involving 4E-BP, eIF4E, and eIF4G is sufficient to explain the changes observed at fertilization on 4E-BP level and on the increase of cap-dependent translation.…”

Serotonin Increases Phosphorylation of Synaptic 4EBP through TOR, but Eukaryotic Initiation Factor 4E Levels Do Not Limit Somatic Cap-Dependent Translation in Aplysia Neurons

“…These results are consistent with findings from sea urchin, the only other invertebrate system in which 4EBP activity has been characterized. In sea urchin, 4EBP phosphorylation and dissociation from eIF4E occur in a rapamycin-sensitive manner following fertilization of sea urchin eggs (18,52,53), an event that triggers a large increase in cap-dependent translation (8).…”

eIF4E et étapes décisionnelles du développement embryonnaire

“…La dégradation de 4E-BP induite par la fécondation est sensible à l'inhibiteur de la kinase FRAP/mTOR, la rapamycine, qui inhibe la première division cellulaire. Enfin, la micro-injection de peptides mimant le site d'association entre 4E-BP et eIF4E dans les ovules affecte, de manière similaire aux effets de la rapamycine, la première division mitotique de l'embryon d'oursin [21]. Ce résultat implique que la libération d'eIF4E de son répresseur 4E-BP est un évé-nement nécessaire à l'entrée dans le cycle cellulaire de l'embryon précoce d'oursin.…”