Stress granules form in Brachionus manjavacas (Rotifera) in response to a variety of stressors.

Many eukaryotes share a common response to environmental stresses. The responses include reorganization of cellular organelles and proteins. Similar stress responses between divergent species suggest that these protective mechanisms may have evolved early and been retained from the earliest eukaryotic ancestors. Many eukaryotic cells have the capacity to sequester proteins and mRNAs into transient stress granules (SGs) that protect most cellular mRNAs (Anderson and Kedersha, 2008). Our observations extend the phylogenetic range of SGs from trypanosomatids, insects, yeast and mammalian cells, where they were first described, to a species of the lophotrochozoan animal phylum Rotifera. We focus on the distribution of three proteins known to be associated with both ribosomes and SG formation: eukaryotic initiation factors eIF3B, eIF4E and T-cell-restricted intracellular antigen 1. We found that these three proteins co-localize to SGs in rotifers in response to temperature stress, osmotic stress and nutrient deprivation as has been described in other eukaryotes. We have also found that the large ribosomal subunit fails to localize to the SGs in rotifers. Furthermore, the SGs in rotifers disperse once the environmental stress is removed as demonstrated in yeast and mammalian cells. These results are consistent with SG formation in trypanosomatids, insects, yeast and mammalian cells, further supporting the presence of this protective mechanism early in the evolution of eukaryotes.