Meiotic resetting of the cellular Sod1 pool is driven by protein aggregation, degradation, and transient LUTI-mediated repression

Abstract

Gametogenesis requires packaging of the cellular components needed for the next generation. In budding yeast, this process includes degradation of many mitotically stable proteins, followed by their resynthesis. Here, we show that one such case—Superoxide dismutase 1 (Sod1), a protein that commonly aggregates in human ALS patients—is regulated by an integrated set of events, beginning with the formation of pre-meiotic Sod1 aggregates. This is followed by degradation of a subset of the prior Sod1 pool and clearance of Sod1 aggregates. As degradation progresses, Sod1 protein production is transiently blocked during mid-meiotic stages by transcription of an extended and poorly translated SOD1 mRNA isoform, SOD1LUTI. Expression of SOD1LUTI is induced by the Unfolded Protein Response, and it acts to repress canonical SOD1 mRNA expression. SOD1LUTI is no longer expressed following the meiotic divisions, enabling a resurgence of canonical mRNA and synthesis of new Sod1 protein such that gametes inherit a full complement of Sod1 protein. Failure to aggregate and degrade Sod1 results in reduced gamete fitness in the presence of oxidants, highlighting the importance of this regulation. Investigation of Sod1 during yeast gametogenesis, an unusual cellular context in which Sod1 levels are tightly regulated, could shed light on conserved aspects of its aggregation and degradation, with relevance to understanding Sod1’s role in human disease.

Control of meiotic entry by dual inhibition of a key mitotic transcription factor

“…In ΔLUTI cells, we observed an increase in the abundance of SWI4 canon mRNA (Figure 5E). This finding corroborates previous reports, where LUTI expression leads to co-transcriptional silencing of the canonical gene promoter, thereby silencing expression of the protein-coding transcript (Chen et al, 2017; Chia et al, 2017; Van Dalfsen et al, 2018; Tresenrider et al, 2021; Vander Wende et al, 2022). Finally, by immunoblotting, we observed an increase in Swi4 protein abundance in the ΔLUTI mutant compared to wild type (Figure 5E and 5F), further indicating that SWI4 LUTI expression downregulates Swi4 protein levels in meiosis.…”

Swi/Snf Chromatin Remodeling Regulates Transcriptional Interference and Gene Repression

“…Case studies have revealed that diverse gene targets are subject to LUTI-based repression, including the genes encoding the kinetochore subunit Ndc80 (J. Chen et al, 2017;Chia et al, 2017), the superoxide dismutase enzyme Sod1 (Vander Wende et al, 2023), the transcription factor Swi4 (Su et al, 2023), and the purine hydrolase enzyme Hnt1 (Van Dalfsen et al, 2018;Tatip et al, 2020). Importantly, the observation that the human protooncogene MDM2 is subject to LUTI-based interference has revealed this form of gene repression is broadly conserved (Hollerer et al, 2019).…”