Abstract
ABSTRACTeIF4E plays a conserved role in initiating protein synthesis, but with multiple eIF4E isoforms present in many organisms, these proteins also adopt specialized functions. Previous RNAi studies showed that ife-3, encoding the sole canonical eIF4E isoform of Caenorhabditis elegans, is essential for viability. Using ife-3 gene mutations, we show here that it is maternal ife-3 function that is essential for embryogenesis, but ife-3 null progeny of heterozygous animals are viable. We find that zygotic ife-3 function promotes body growth and regulates germline development in hermaphrodite worms. Specifically, the normal transition from spermatogenesis to oogenesis in the hermaphrodite germline fails in ife-3 mutants. This failure to switch is reversed by inhibiting expression of the key masculinizing gene, fem-3, suggesting ife-3 resembles a growing number of genes that promote the sperm/oocyte switch by acting genetically as upstream inhibitors of fem-3.
Highlights
Eukaryotic initiation factor 4-complex recruits mature mRNAs to ribosomes as the first step of translation (Gingras et al, 1999)
The nematode Caenorhabditis elegans encodes five eIF4E proteins (IFE-1 to -5) that reflect a diversity partially conserved across the animal kingdom: IFE-3 resembles the canonical eIF4E-1 isoforms of mammals and insects; IFE-4 is a member of the divergent 4E-HP group of eIF4E proteins; and IFE-1, -2, and -5 are closely related isoforms that make a nematode-specific sub-group (Hernández and Vazquez-Pianzola, 2005; JankowskaAnyszka et al, 1998; Keiper et al, 2000)
No identified point mutations or small deletions in XA8002 are likely to cause sterility, but over several regions near daam-1, the sequence coverage was decreased approximately 50%, suggesting these regions are deleted from one copy of Chromosome V (ChrV) in XA8002 (Fig. 1A, supplementary material Table S2)
Summary
Eukaryotic initiation factor 4-complex (eIF4) recruits mature mRNAs to ribosomes as the first step of translation (Gingras et al, 1999). The factor eIF4E recognizes a methylated guanosine cap at the mRNA 5′ end, aiding recruitment of the complex to the mRNA. Multiple eIF4E homologs are common among organisms (Hernández and Vazquez-Pianzola, 2005), allowing them to adopt specialized functions. IFE-2 is enriched in the soma, and functions in the germline. Its loss inhibits general somatic mRNA translation, as well as temperature-dependent translation of germline mRNAs required for meiotic crossover repair (Hansen et al, 2007; Song et al, 2010; Syntichaki et al, 2007).
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