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This protocol describes the use of fluorescence recovery after photobleaching (FRAP) to investigate the dynamics of Matrin-3 (MATR3) condensates in live budding yeast. We detail how to generate yeast strains containing MATR3 with an enhanced green fluorescent protein (eGFP) tag and induce MATR3-eGFP expression. We provide steps to prepare slides of immobilized yeast cells and perform FRAP imaging and data analysis. This protocol can be broadly applied to study condensate dynamics of a range of proteins in different model systems. For complete details on the use and execution of this protocol, please refer to Sprunger et al. (2022)., Competing Interests: The authors declare no competing interests., (© 2022 The Author(s).)

Matrin-3 (MATR3) is a DNA- and RNA-binding protein implicated in amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and distal myopathy. Here, we report the development of a yeast model of MATR3 proteotoxicity and aggregation. MATR3 is toxic and forms dynamic shell-like nuclear condensates in yeast. Disease-associated mutations in MATR3 impair condensate dynamics and disrupt condensate morphology. MATR3 toxicity is largely driven by its RNA-recognitions motifs (RRMs). Further, deletion of one or both RRMs drives coalescence of these condensates. Aberrant phase separation of several different RBPs underpins ALS/FTD, and we have engineered Hsp104 variants to reverse this misfolding. Here, we demonstrate that these same variants also counter MATR3 toxicity. We suggest that these Hsp104 variants which rescue MATR3, TDP-43, and FUS toxicity might be employed against a range of ALS/FTD-associated proteins. We anticipate that our yeast model could be a useful platform to screen for modulators of MATR3 misfolding., Competing Interests: The authors declare no competing interests., (© 2022 The Author(s).)

In Mutant INS-gene-induced Diabetes of Youth (MIDY) syndrome, mutant proinsulin aggregates interfere with the folding of wild-type proinsulin in the endoplasmic reticulum, ultimately decreasing insulin secretion. In this issue of Molecular Cell, Cunningham et al. (2019) identify two mechanisms by which prohormone aggregation is prevented and cleared., (Copyright © 2019 Elsevier Inc. All rights reserved.)