Cytoplasmic Dynein Is Required for the Spatial Organization of Protein Aggregates in Filamentous Fungi

Abstract

SUMMARY Eukaryotes have evolved multiple strategies for maintaining cellular protein homeostasis. One such mechanism involves neutralization of deleterious protein aggregates via their defined spatial segregation. Here, using the molecular disaggregase Hsp104 as a marker for protein aggregation, we describe the spatial and temporal dynamics of protein aggregates in the filamentous fungus Aspergillus nidulans. Filamentous fungi, such as A. nidulans, are a diverse group of species of major health and economic importance and also serve as model systems for studying highly polarized eukaryotic cells. We find that microtubules promote the formation of Hsp104-positive aggregates, which coalesce into discrete subcellular structures in a process dependent on the microtubule-based motor cytoplasmic dynein. Finally, we find that impaired clearance of these inclusions negatively impacts retrograde trafficking of endosomes, a conventional dynein cargo, indicating that microtubule-based transport can be overwhelmed by chronic cellular stress.

The Aspergillus nidulans bimC4 mutation provides an excellent tool for identification of kinesin-14 inhibitors

“…Alternatively, one can introduce the human HSET/KIFC1 gene into A. nidulans , and if it can functionally substitute for klpA , a bimC 4 mutant containing this human gene would be ideally suited for directly identifying HSET/KIFC1 inhibitors. A. nidulans is a well established genetic system for studying mitosis and microtubule motors in general (Morris, 1975; Enos and Morris, 1990; O’Connell et al, 1993; Oakley, 2004; Osmani and Mirabito, 2004; Xiang and Fischer, 2004; Peñalva et al, 2012; Pantazopoulou et al, 2014; Steinberg, 2014; Egan et al, 2015; Xiang et al, 2015) and A. nidulans -based drug screening has been performed previously (Kiso et al, 2004; Mircus et al, 2009; Zhai et al, 2010), further supporting the feasibility of our proposed kinesin-14 inhibitor screen.…”

Peroxisomes move by hitchhiking on early endosomes using the novel linker protein PxdA

“…Video 6). We also occasionally observed instances where a moving PxdA puncta paused at a nonmotile peroxisome, an event that was followed by the movement of co-migrating PxdA and the peroxisome ( Because we observed many more moving PxdA puncta than moving peroxisomes and because PxdA motility was reminiscent of endosome motility (Abenza et al, 2009;Egan et al, 2015;Egan et al, 2012b;Zhang et al, 2010), we next asked whether PxdA also colocalizes with endosomes. To test this, we analyzed kymographs from simultaneous time-lapse movies of labeled PxdA and endosomes (Video 7).…”

Mechanism and Regulation of Cytoplasmic Dynein

“…Dynein also transports mRNAs (Holt & Bullock 2009) and assembles and transports stress granules and processing bodies involved in RNA homeostasis (Loschi et al 2009). Likewise, protein homeostasis requires dynein to transport protein aggregates (Egan et al 2015, Johnston et al 2002). Many viruses, including herpes simplex virus (HSV-1) and human immunodeficiency virus type 1 (HIV-1), recruit dynein to move toward the nucleus (Dodding & Way 2011).…”