A conserved triple arginine motif in OMA-1 is required for RNA-binding activity and embryo viability

Sexually reproducing organisms make haploid gametes—oocytes and spermatocytes—that combine during fertilization to make an embryo. While both gametes contain similar DNA content, oocytes contain the bulk of the cytoplasm including maternally supplied mRNAs and proteins required prior to zygotic gene activation. RNA-binding proteins are key regulators of these maternal transcripts. In Caenorhabditis elegans , the tandem zinc finger proteins OMA-1 and OMA-2 are required for fertilization. Here, we show that OMA-1 RNA-binding activity requires a short basic region immediately up-stream from the canonical tandem zinc finger domain. Mutation of this region in animals produces a phenotype distinct from a genetic null. Oocytes can be fertilized, but fail to form an intact chitin egg-shell, frequently break in utero, and arrest prior to morphogenesis. Our results identify a critical region outside of the canonical RNA-binding domain required for both RNA-binding activity as well as revealing a new role for OMA-1 during the oocyte-to-embryo transition.