ABSTRACT
Stress granules (SGs) and P-bodies (PBs) are related cytoplasmic structures harboring silenced mRNAs. SGs assemble transiently upon cellular stress, whereas PBs are constitutive and are further induced by stress. Both foci are highly dynamic, with messenger ribonucleoproteins (mRNPs) and proteins rapidly shuttling in and out. Here, we show that impairment of retrograde transport by knockdown of mammalian dynein heavy chain 1 (DHC1) or bicaudal D1 (BicD1) inhibits SG formation and PB growth upon stress, without affecting protein-synthesis blockage. Conversely, impairment of anterograde transport by knockdown of kinesin-1 heavy chain (KIF5B) or kinesin light chain 1 (KLC1) delayed SG dissolution. Strikingly, SG dissolution is not required to restore translation. Simultaneous knockdown of dynein and kinesin reverted the effect of single knockdowns on both SGs and PBs, suggesting that a balance between opposing movements driven by these molecular motors governs foci formation and dissolution. Finally, we found that regulation of SG dynamics by dynein and kinesin is conserved in Drosophila.
Subject(s)
Cytoplasmic Structures/metabolism , Dyneins/metabolism , Kinesins/metabolism , Microtubule-Associated Proteins/metabolism , Animals , Cytoplasmic Structures/genetics , Drosophila Proteins , Dyneins/genetics , Kinesins/genetics , Mice , Microtubule-Associated Proteins/genetics , NIH 3T3 Cells , Protein BiosynthesisABSTRACT
Gene expression in trypanosomatids is mainly regulated post-transcriptionally. One of the mechanisms involves the differential stability of mRNAs. However, the existence of other mechanisms involving the accessibility of mRNAs to the translation machinery cannot be ruled out. Defined cytoplasmic foci containing non-translating mRNPs, known as P-bodies, have been discovered in recent years. P-bodies are sites where mRNA can be decapped and 5'-3' degraded or stored for subsequent return to polysomes. The highly conserved DEAD box helicase Dhh1p is a marker protein of P-body functions. Here, we report the identification and cloning of a Trypanosoma cruzi Dhh1 homolog gene. TcDhh1 expression is not regulated through the parasite life cycle or under stress conditions. We show that TcDhh1 is present in polysome-independent complexes and is localized to discrete cytoplasmic foci, resembling P-bodies; these foci vary in number according to nutritional stress conditions and cycloheximide/puromycin treatment.