Stress granules (SG) form in eukaryotic cells as a stress-response mechanism to halt and protect protein translation. SGs are membrane-free associations of mRNA and RNA-binding proteins that aggregate in the cytosol, although their assembly mechanism in vivo is still poorly studied. Now, Nicholas Sokol and colleagues (Buddika et al., 2020) identify novel SG structures in Drosophila intestinal progenitor cells, termed intestinal progenitor SGs (IPSGs). These contain the fly orthologues of different mammalian SG proteins, such as ataxin-2 (ATX2), T-cell internal antigen-1 (TIA1; ROX8 in Drosophila), and Ras GTPase-activating protein-binding protein (G3BP; RIN in Drosophila), among others. In the absence of stress, these proteins are enriched in the cytosol of the progenitor cells, whereas neighbouring differentiated cells show lower levels of the SG markers. When progenitor cells are exposed to the stress-inducers sodium arsenite or rapamycin, several of these SG proteins aggregate in large granules in the cytosol, resembling SGs seen in other cells. In addition, IPSGs share other SG features, such as mRNA aggregation, reduced protein synthesis and reversible disassembly after stress. Surprisingly, ATX2, RIN and ROX8, whose orthologues are essential for SG assembly, are not required for IPSG formation, pointing to a non-canonical mechanism. Taken together, this work provides novel insights into SG assembly and specificity in different cellular contexts.

• © 2020. Published by The Company of Biologists Ltd