Conserved elements in the nanos3 3′UTR of olive flounder are responsible for the selective retention of RNA in germ cells

In teleost fish, primordial germ cells (PGCs) are specified very early during embryogenesis and migrate to the site that gonads are formed. A previous study indicated that nanos3 is specifically expressed in PGCs, and the 3′ untranslated region (UTR) of nanos3 is responsible for the localization of mRNA in these cells. In this study, we aimed to investigate the functional regions of nanos3 3′UTR in olive flounder using truncated and mutated nanos3 3′UTRs fused to chimeric RNAs and microinjected into fertilized zebrafish eggs. The results indicated that a 68-bp functional element in the nanos3 3′UTR of olive flounder played important roles in the protection and degradation of RNA. Within this element, a U-rich region was identified to be responsible for the protection of RNA in PGCs and two GCAC sites for the degradation of RNA in somatic cells. The first GCAC was located adjacently to the U-rich region and the second GCAC within the U-rich region. Overall, we concluded that the two GCACs were the binding sites of miR-430, a microRNA that suppresses translation, whereas the U-rich region was the binding site of Dnd, a protein that antagonizes the miR-430-mediated silencing of mRNA.