Evaluation of current descriptions of peroxisomal biogenesis and inheritance in S. cerevisiae: a tale of two models

The peroxisome is an organelle conserved across Eukaryota. Ever since their discovery, the scientific consensus regarding the processes through which peroxisomes are formed and are inherited has changed several times. It is now known that peroxisomes are either produced though fission of pre-existing ones or de novo from the endoplasmic reticulum (ER). However, the relative importance of these processes and the conditions in which they occur is still a subject of much debate. This has led to the proposal of several models attempting to explain the situation, predominantly supported through evidence gathered studying the budding yeast Saccharomyces cerevisiae. An evaluation of some of the proposals of these models in yeast is the main thread of this study. One such model proposed that the division and inheritance of peroxisomes are coupled processes guaranteeing that the same number of peroxisomes is maintained through multiple generations; another suggested that the de novo synthesis of peroxisomes occurs continuously in S. cerevisiae by the fusion of previously unrecognised heterotypic vesicles, an observation which disagrees with much of the other evidence gathered regarding the process in the organism. To address these questions, a system of imaging multiple generations of S. cerevisiae cells was necessary, alongside the creation of a computer-assisted workflow to analyse and quantify these and other images of peroxisomes and cells. Results from the long time-lapse live-cell imaging experiments show that the behaviour of peroxisomes is complex and that a direct relationship between division and inheritance is hard to demonstrate in practice, especially with techniques currently available. Moreover, live-cell experiments in conjunction with computer-quantified images corroborated previous evidence regarding the process of de novo synthesis and demonstrated the lack of de novo synthesis in cells already containing peroxisomes. Overall, this study shows the usefulness of live cell imaging and computerised analysis for studying peroxisomes. It showcases what can currently be concluded using these techniques for studying this organelle in S. cerevisiae, examines the limitations of the restrictions of spatial and temporal resolutions, and explores what progress is necessary to decipher the peroxisome biogenesis and inheritance situation in the future