During the final stages of oocyte growth, these germ cells become transcriptionally inactive while preparing to resume meiosis and jumpstart their maturation into eggs. At this austere time, oocytes can only use maternal messenger RNAs (mRNAs) they have previously stored to get through their maturation process and early embryonic development if fertilized. Oocytes from the worm Caenorhabditis elegans store mRNA in P granules, those of fruit flies do so in polar granules, and aquatic frogs and zebrafish rely on a structure called the Balbiani body—all of which are membraneless organelles. But for mammals, the storage site has been terra incognita so far.
Maternal mRNA has previously been reported to be present in the cell’s cortex—a boundary zone that includes the cell membrane and cytoplasm—and the nucleus of mammalian oocytes, but without conclusive evidence that either of these cellular spaces is the site of RNA storage. A study published online today ...
