Early Developmental Expression of Mus musculus Zinc Finger RNA-Binding Protein Compared to Orthologs in Caenorhabditis elegans and Danio rerio and Subcellular Localization of Mus musculus and Caenorhabditis elegans Zinc Finger RNA-Binding Protein in 2-Cell Mus musculus Embryos

In mouse, knock-out of the Zfr gene encoding the zinc finger RNA-binding protein ( ZFR) is associated with early lethality during gastrulation, suggesting that a pool of maternally contributed Zfr mRNA might compensate to allow development. ZFR is an ancient and highly conserved chromosome-associated protein from nematodes to mammals. We characterized expression of the Zfr transcript during early development in Mus musculus, Danio rerio, and Caenorhabditis elegans by quantitative real-time polymerase chain reaction. Mouse Zfr mRNA was detected in all stages tested during mouse preimplantation, with higher levels at the 1-cell stage that includes the maternal contribution of Zfr mRNA. In D. rerio, Zfr mRNA expression was highest in unfertilized eggs and declines throughout development. In C. elegans, Zfr mRNA expression was barely detectable in the fertilized egg and the L1 stage, but increased in the adult organism. Microinjections of green fluorescent protein (GFP)-tagged versions of in vitro-transcribed mouse and C. elegans Zfr mRNAs into early mouse embryos allowed analysis of the intracellular localization of the protein. Mouse ZFR-GFP was localized in the nucleus in 2-cell stage embryos although absent from nucleoli. Deletion studies revealed that this nuclear localization required the C-terminal part of ZFR, as deletion of the C-terminal resulted in the localization to the nuclear membrane. Despite the lack of a conserved nuclear localization signal, the C. elegans ZFR-GFP fusion protein also displayed an intranuclear localization in the 2-cell mouse embryo.