Maternal genes in Caenorhabditis elegans determine the polarity of the embryo before the 12-cell stage. The maternal gene
spn-4 encodes a protein containing an RNA-binding domain and is required for normal cytokinesis and spindle orientation in early embryos. SPN-4 binds the region in the 3'-UTR and forms a complex with POS-1. This complex is required for maternal
glp-1 mRNA translation in anterior blastomeres of early embryos. Furthermore, SPN-4 regulates the translation of other maternal genes. However, many molecular mechanisms of the maternal genes are still unknown. We therefore performed shotgun proteomic analyses with isobaric tags for relative and absolute quantitation (iTRAQ), to identify the group of genes whose translation is regulated by SPN-4. iTRAQ analysis was performed once for each of the 2 samples, corresponding to embryonic and adult stages,
and1121 proteins were identified. The proteins were classified intoup-regulated and down-regulated expression levels of the proteins in
spn-4 mutant compared to that in wild-type. We focused on 61 proteins whose expressions were down-regulated at the embryo stage in the mutant. STRING and NEXTDB databases were used to investigate the functional clusters with protein-protein interactions and in situ hybridization patterns, respectively, among the proteins. We obtained 6 functional clusters by using STRING. Among them, RNA-binding protein CAR-1, which is required for early embryonic cytokinesis, and
spn-4 interacting protein Y18D10A.11 form a cluster. The other cluster includes kinetochore-binding proteins, KBP-3 and KBP-4, which are expressed in mitotic spindles. These 4 proteins are related to mitotic division. Furthermore, we confirmed mRNA expression of 61 genes in the gonad by using NEXTDB. The expression patterns of 37 genes indicated that these genes were maternal. There are 19 genes, including
car-1,
kbp-3, and
kbp-4, with the embryonic lethal phenotypes on WORMBASE. Collectively, our results suggest that these 3 genes are important for cell-fate determination and that their translation is closely regulated by SPN-4.