Evolutionary origin and phylogenetic analysis of the novel oocyte-specific eukaryotic translation initiation factor 4E in Tetrapoda - PubMed (original) (raw)

Evolutionary origin and phylogenetic analysis of the novel oocyte-specific eukaryotic translation initiation factor 4E in Tetrapoda

Alexei V Evsikov et al. Dev Genes Evol. 2009 Feb.

Abstract

The transcriptionally active, growing oocyte accumulates mRNAs essential for early stages of development, the oocyte-to-embryo transition, in a stable, dormant form. Translational repression of mRNAs in eggs of various species is conferred by interactions, either direct or via intermediate proteins, of repressive factors bound to the 3'-untranslated regions with the proteins of the eukaryotic translation initiation factor 4E (eIF4E) family bound to the 5'-cap of the transcripts. Recently, a novel oocyte-specific eIF4E encoded by the Eif41b gene in mammals has been identified by our group. To further investigate this gene, the available cDNA libraries, as well as genome assemblies of nonmammalian vertebrates, were surveyed. This analysis revealed that the Eif4e1b gene arose in Tetrapoda as a result of the ancestral Eif4e locus duplication. Unlike other known proteins of three subfamilies comprising eIF4E family (eIF4E1, eIF4E2, and eIF4E3), cDNA library evidence suggests that Eif41b locus has an oocyte-restricted expression across all classes of Tetrapoda. To further understand the role of eIF4E1B during oocyte maturation, injections of antisense morpholino nucleotides in the X. tropicalis fully-grown stage VI oocytes were performed. The resulted ablation of eIF4E1B protein led to significant acceleration of oocyte maturation after progesterone induction; morpholino-injected oocytes formed the metaphase plate 30 min faster than the control groups. These results suggest that eIF4E1B protein acts as a repressor in translational regulation of maternal mRNAs activated during, and required for, oocyte maturation.

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Figures

Figure 1

Figure 1. Conservation of genomic structure for Eif4e and Eif4e1b loci in Tetrapoda

Colinearity of genes underscores the common phylogenetic origins for Eif4e (a) and Eif4e1b (b) in tetrapods. (c) The Danio rerio eif4e1b locus is not conserved among Actinopterygii genomes. (d) While the colinearity of Sncb and Tspan17 orthologs persists across vertebrates, fish genomes lack the Eif4e1b locus. Orthologs shown in the same color; non-orthologous genes shown in black.

Figure 2

Figure 2. Actinopterigyii genomes contain multiple members of eIF4E1 subfamily

Danio rerio expresses at least four members of this family (Suppl. Table 1), three of which have orthologs in other sequenced fish genomes. Genomic arrangement of loci for putative orthologs of zebrafish eif4e1a (Eif4e1_1) (a), zgc:101581 (Eif4e1_2) (b) and zgc:110154 (Eif4e1_3) (c) genes. Orthologs shown in the same color; non-orthologous genes shown in black.

Figure 3

Figure 3. Gene expression of Eif4e1b and its function in oocytes of Xenopus tropicalis

(a) RT-PCR detection of eIF4E-encoding genes (Xt_Eif4e1b, Xt_Eif4e, Xt_Eif4e2a, Xt_Eif4e2b, Xt_Eif4e3), Xt-Gpcr13, Xt-Odc as positive controls of cDNA quality and H2O as a negative control. (b, c) Effects of blocking eIF4E1B translation on the resumption of meiosis and maturation in oocytes exposed to anti-Eif4e1b morpholino or control for two and four days.

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