Granule regulation by phase separation during Drosophila oogenesis - PubMed (original) (raw)
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Granule regulation by phase separation during Drosophila oogenesis
M Sankaranarayanan et al. Emerg Top Life Sci. 2020.
Abstract
Drosophila eggs are highly polarised cells that use RNA-protein complexes to regulate storage and translational control of maternal RNAs. Ribonucleoprotein granules are a class of biological condensates that form predominantly by intracellular phase separation. Despite extensive in vitro studies testing the physical principles regulating condensates, how phase separation translates to biological function remains largely unanswered. In this perspective, we discuss granules in Drosophila oogenesis as a model system for investigating the physiological role of phase separation. We review key maternal granules and their properties while highlighting ribonucleoprotein phase separation behaviours observed during development. Finally, we discuss how concepts and models from liquid-liquid phase separation could be used to test mechanisms underlying granule assembly, regulation and function in Drosophila oogenesis.
Keywords: RNP granules; developmental biology; phase separation.
© 2020 The Author(s).
Conflict of interest statement
The authors declare that there are no competing interests associated with the manuscript.
Figures
Figure 1.. Schematic and role of maternal granules in egg chambers.
Nuage is localised around the nurse cell nuclei, while sponge bodies are dispersed throughout the cytoplasm of the nurse cells. P bodies are enriched at the anterior margin of the oocyte (especially in the dorso-anterior corner). They are also observed throughout the oocyte and nurse cell cytoplasm. Polar granules are present at the posterior pole of the oocyte. Fifteen nurse cells, positioned to the anterior, produce the components (mRNAs, proteins, etc.) required for the development of a single oocyte. These germline-derived cells are interconnected through cytoskeletal bridges, allowing for cytoplasmic movement between them, and are surrounded by somatic-derived layer of follicle cells. (Representative cell types of the egg chamber are outlined with black dotted lines. Representative nuclei are outlined with white dotted lines and marked with an ‘n’). Created in BioRender.
Figure 2.. Model for RNP granule assembly and maturation in Drosophila egg chambers.
In the cytoplasm, key scaffolding proteins and mRNAs, through multivalent interactions, come together to form RNP complexes. Multiple RNP complexes nucleate to assemble a primary granule via LLPS. Depending on the partitioning of specific client proteins and RNAs, granule diversity may be achieved. Although client-scaffold interactions may already be present during primary granule assembly, our model proposes that higher partitioning of clients regulate granule material states by modulating the strength of the resulting molecular interactions. While liquid-like and gel-like physical states are more commonly observed in vivo, other material states can exist based on specific developmental and environmental cues. Created in BioRender.
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