Theses Doctoral

Rie1 and Sgn1 form an RNA-binding complex that enforces the meiotic entry cell fate decision

Gaspary, Alec

Budding yeast cells have the capacity to adopt distinct physiological states depending on environmental conditions. Vegetative cells proliferate rapidly by budding while spores can survive prolonged periods of nutrient deprivation and/or desiccation. Whether or not a yeast cell will enter meiosis and sporulate represents a critical decision which could be lethal if made in error. Most cell fate decisions, including those of yeast, are understood as being triggered by the activation of master transcription factors. However, mechanisms that enforce cell fates post-transcriptionally have been more difficult to attain. Here, we perform a forward genetic screen to determine RNA-binding proteins that affect meiotic entry at the post-transcriptional level. Our screen revealed several candidates with meiotic entry phenotypes, the most significant being RIE1 which encodes an RRM-containing protein.

We demonstrate that Rie1 binds RNA, is associated with the translational machinery, and acts post-transcriptionally to enhance protein levels of the master transcription factor Ime1 in sporulation conditions. We also identified a physical binding partner of Rie1, Sgn1, which is another RRM (RNA Recognition Motif)-containing protein that plays a role in timely Ime1 expression. We demonstrate that these proteins act independently of cell size regulation pathways to promote meiotic entry. We propose a model explaining how constitutively expressed RNA-binding proteins, such as Rie1 and Sgn1, can act in cell-fate decisions both as switch-like enforcers and as repressors of spurious cell fate activation.

Chapter 1 serves as a brief overview of the importance cell fate decisions and details how sporulation in the budding yeast Saccharomyces cerevisiae can be used as a model to understand the pathways and mechanisms underlying these decisions. This chapter focuses on the importance of the meiotic master regulator IME1 and the different effectors of regulation that govern its expression at the transcriptional and post-transcriptional levels.

Chapter 2 describes the significance of RNA binding proteins and how they can influence cell fate decisions with a focus on cell cycle modifications that shift mitosis to meiosis. Chapter 3 explains the methodology that I used to discover two RNA-binding proteins that play key roles in meiotic entry: Rie1 and Sgn1. Chapter 4 describes my work to dissect the pathways governed by Rie1 and Sgn1. Chapter 5 discusses the potential mechanisms by which Rie1 and Sgn1 could drive entry into meiosis. Collectively, the studies described in this thesis demonstrate that Rie1 and Sgn1 affect the cell fate decision to enter meiosis in budding yeast by activating as translational activators of IME1.

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More About This Work

Academic Units
Genetics and Development
Thesis Advisors
Berchowitz, Luke E.
Degree
Ph.D., Columbia University
Published Here
July 12, 2023