Spatiotemporal regulation of organelle transport in Saccharomyces cerevisiae

Abstract

Eukaryotic cells possess diverse membrane-bound compartments called organelles, which play crucial roles in facilitating specialised biochemical processes necessary for maintaining cellular metabolism under different growth conditions. Consequently, cells have evolved specific molecular mechanisms to control organelle inheritance and maintenance during the process of cell growth and division. Proper transport of organelles to their designated locations in dividing cells is crucial for maintaining a full complement of organelles across multiple cell generations. Dysfunctional organelle inheritance or maintenance has been linked to numerous human diseases. Saccharomyces cerevisiae, has been extensively used to study organelle-related processes, leading to a deeper understanding of fundamental concepts underlying organelle inheritance and functions. Furthermore, it is recognised that many core principles regarding organelle inheritance and maintenance are conserved throughout eukaryotic evolution.

The first part of this research focuses on the transport of vacuoles and peroxisomes by studying the interactions between Class V myosin, Myo2, and its vacuolar and peroxisomal adaptors, Vac17 and Inp2, which are essential for organelle transport. Experimental validations confirm the significance of specific regions in Vac17 and Inp2, known as Myo2 interaction sites (MIS), for vacuole and peroxisome transport. This helped us to generate MIS tools that could be used to study the regulation of vacuole and peroxisome transport from the mother cell during the early stages of organelle transport.

Additionally, by utilising the generated MIS tools, the thesis examines the influence of the protein kinase Kin4 and its paralog Frk1 on vacuole and peroxisome inheritance. The study demonstrates that Kin4 and Frk1 play a crucial role in stabilizing Vac17 and Inp2 in the mother cell by preventing their early degradation during organelle transport. These findings provide insights into the function of Kin4 in antagonizing the role of Cla4 during vacuole and peroxisome inheritance.

Furthermore, the research aims to identify novel factors involved in vacuole and peroxisome transport. To accomplish this, an overexpression screen was conducted, which led to the identification of new genes associated with peroxisome and vacuole inheritance. This comprehensive analysis sheds light on the forward transport and retention of organelles. Notably, the study also identifies Yck1 and its paralog Yck2 as novel factors potentially involved in regulating peroxisome retention by influencing the function of Inp1, a peroxisomal membrane protein essential for peroxisome retention.