GLA-3 mediates the heat shock response in Caenorhabditis elegans germ cells: A key role for the tristetraprolin (TTP) family

Abstract

Tristetraprolin or TTP is an RNA-binding protein that possesses two CCCH-like zinc-finger domains that bind AU-rich elements to promote their degradation. One of its targets is the mRNA of tumor necrosis factor alpha (TNF-α). When TTP is absent, the TNF-α factor accumulates causing severe, generalized inflammation in knockout mice. TTP is also considered a tumor suppressor protein because it regulates the expression of several mRNAs that encode for proteins involved in cell cycle regulation and it is downregulated in various types of human cancers. Under stress, TTP associates with stress granules (SGs), dynamic cytoplasmic condensates formed by liquid-liquid phase separation (LLPS) that protect mRNAs from harmful conditions. Despite TTP’s important role in mRNA turnover, much remains to be explored about its participation in stress resistance in living animals. For this reason, we investigated the role of GLA-3, one of TTP’s homologs, in the nematode Caenorhabditis elegans during the heat shock response. Previously, it has been shown that nematodes lacking gla-3 /TTP exhibit phenotypes such as progressive loss of motility, reduced brood size, and increased embryonic lethality. As well as defects in meiotic progression, and increased germ-cell apoptosis. Here, we show that a GFP::GLA-3 reporter is primarily expressed in the C. elegans germline. During heat shock, GLA-3 localizes to condensates that contain both processing bodies, sites of mRNA storage and decay, and stress granules. We demonstrate that, in the C. elegans gonad under heat shock conditions, the canonical P body marker CGH, the DDX6 homolog, associates with GLA-3, as well as with the canonic stress markers TIAR-1/TIA1 and GTBP-1/G3BP. These data show that in C. elegans , P bodies and stress granules colocalize during heat shock. Similarly, in yeast, P bodies and stress granules fuse during stress, suggesting that C. elegans induces condensates that resemble those observe in yeast. Additionally, we demonstrate that GLA-3 is important for the formation of both P bodies and stress granules. Finally, we show that oogenic germ cells of GLA-3 mutant animals that were exposed to heat shock resulted in embryos that did not survive, showing that GLA-3 plays an important role in protecting germ cells from this condition. Our results demonstrate that the role of GLA-3 is conserved in C. elegans , and this model can be very useful for further investigating the role of this protein in the future.