Get it together: How RNA-binding proteins assemble and regulate germ plasm in the oocyte and embryo

In zebrafish, the sequential processes of oocyte maturation, egg fertilization, and early embryonic development take place while the genome is transcriptionally silent. Proper development and patterning of the oocyte and embryo requires that the numerous gene products (RNAs and proteins) that regulate oocyte and early embryonic development are produced prior to genome inactivation and are preserved and utilized in the time and place where they are needed. During this period the oocyte and eventual embryo relies on posttranscriptional and posttranslational mechanisms. Prominent regulators are the various RNA-binding proteins (RNAbps) that assemble their RNA targets into ribonucleoprotein (RNP) granules where they are localized, protected, translated or degraded. In oocytes and embryos, these RNP granules are enriched in an electron-dense portion of cytoplasm termed germ plasm, so-called because its contents include the molecules that induce formation of future germ cells. In this chapter, we will review the roles of RNAbps and posttranscriptional regulation in the germ plasm of developing zebrafish oocytes and embryonic primordial germ cells.