Erika Tsukamoto

After the sperm fertilizes the egg cell (oocyte), the newly fertilized embryo undergoes changes in chromosomal composition and gene expression that are required for embryonic development called the oocyte-to-embryo transition (OET). Defects in the OET cause infertility, miscarriage, and birth defects in humans. Molecules carrying genetic information inherited from the mother in the form of maternal mRNA are important for early embryonic development. Early-acting maternal mRNA that have completed their function are rapidly degraded during the OET to allow other mRNA to be expressed. However, the complete mechanism of maternal mRNA degradation is not fully understood. In the nematode Caenorhabditis elegans, SPN-4 is a highly conserved RNA-binding protein that is required for maternal mRNA degradation. Many mRNAs that associate with SPN-4 are rapidly degraded after fertilization. Thus, we investigated how SPN-4 manages to clear these mRNA by using a genetic screen. We mutagenized the genome, looked for changes in observable characteristics, and correlated characteristic changes to mutations found in genes. We identified candidate genes through whole genome sequencing and bioinformatics. We found that two candidate genes encode essential subunits of the CCR4-NOT deadenylase complex which promotes mRNA degradation. We verified these genes by creating mutations in them using CRISPR-Cas9 gene editing. Our data shows that the CCR4-NOT deadenylase complex is involved in maternal mRNA degradation in addition to SPN-4. Our current prediction is that the SPN-4 RNA-binding protein plays an important role in targeting specific mRNAs for degradation by recruiting the CCR4-NOT deadenylase complex to these mRNAs during the OET. Further studies into the binding specificity of SPN-4 to certain mRNA are currently underway.